Next Issue
Previous Issue

Table of Contents

Metals, Volume 8, Issue 3 (March 2018)

  • Issues are regarded as officially published after their release is announced to the table of contents alert mailing list.
  • You may sign up for e-mail alerts to receive table of contents of newly released issues.
  • PDF is the official format for papers published in both, html and pdf forms. To view the papers in pdf format, click on the "PDF Full-text" link, and use the free Adobe Readerexternal link to open them.
Cover Story (view full-size image) Shot peening is a surface treatment commonly used to improve the fatigue behaviour of mechanical [...] Read more.
View options order results:
result details:
Displaying articles 1-50
Export citation of selected articles as:

Research

Jump to: Review

Open AccessArticle Tribological Behavior of Nano-Sized SiCp/7075 Composite Parts Formed by Semisolid Processing
Metals 2018, 8(3), 148; doi:10.3390/met8030148
Received: 26 December 2017 / Revised: 18 January 2018 / Accepted: 17 February 2018 / Published: 25 February 2018
PDF Full-text (21042 KB) | HTML Full-text | XML Full-text
Abstract
The tribological behavior of the rheoformed and thixoformed nano-sized SiCp/7075 composite parts is investigated. The semisolid stirring temperature has a little influence on the friction coefficient and wear resistance of the rheoformed composite parts. As for the thixoformed composite parts, the
[...] Read more.
The tribological behavior of the rheoformed and thixoformed nano-sized SiCp/7075 composite parts is investigated. The semisolid stirring temperature has a little influence on the friction coefficient and wear resistance of the rheoformed composite parts. As for the thixoformed composite parts, the average value of the steady-state coefficient of friction increases firstly and then decreases with increasing reheating temperature. Higher wear resistance is achieved at a reheating temperature of 580 °C. The average value of the steady-state friction coefficient of the rheoformed composite parts varies from 0.37 to 0.45 upon applied loads of from 20 to 50 N. Weight loss increases slightly upon an increase of applied load from 20 to 40 N. An applied load of 50 N leads to a significant increase of the weight loss. The wear rate decreases firstly and then increases with increasing applied load. As for the thixoformed composite part, the average value of the steady-state friction coefficient and the weight loss decreased with an increasing applied load. However, the wear rate decreases firstly with increasing applied load and then increases. As for the rheoformed composite part, the average value of the steady-state friction coefficient decreases firstly and then increases a little with increasing sliding velocity. Weight loss and wear rate show a first increase and a followed decrease with increasing sliding velocity. As for the thixoformed composite part, the average value of the steady-state friction coefficient shows a decrease with increasing sliding velocity. Weight loss and wear rate exhibit, at first, an increase, and then a decrease with increasing sliding velocity. The average friction coefficient varies from 0.4 to 0.44 with increasing volume fraction of SiC. Weight loss and wear rate decrease with increasing volume fraction of SiC. An increase in dislocation density around the nano-sized SiC particles and the mismatch of the coefficient of thermal expansion (CTE) between 7075 matrix and nano-sized SiC particles during solidification improve the wear resistance of the composite. The dominant wear mechanisms of the rheoformed and thixoformed composite parts are adhesive wear, abrasive wear and delamination wear. Full article
(This article belongs to the Special Issue Semi-solid Processing of Alloys and Composites)
Figures

Figure 1a

Open AccessArticle Enhanced Corrosion Resistance of Ultrafine-Grained Fe-Cr Alloys with Subcritical Cr Contents for Passivity
Metals 2018, 8(3), 149; doi:10.3390/met8030149
Received: 29 January 2018 / Revised: 24 February 2018 / Accepted: 24 February 2018 / Published: 26 February 2018
PDF Full-text (23141 KB) | HTML Full-text | XML Full-text
Abstract
This work presents an experimental validation that an ultrafine grained (UFG) structure of binary Fe-Cr alloys fabricated by severe plastic deformation (SPD) can bring about dramatic improvements in the corrosion resistance. More specifically, UFG Fe-Cr alloys with subcritical chromium content for passivation (8%
[...] Read more.
This work presents an experimental validation that an ultrafine grained (UFG) structure of binary Fe-Cr alloys fabricated by severe plastic deformation (SPD) can bring about dramatic improvements in the corrosion resistance. More specifically, UFG Fe-Cr alloys with subcritical chromium content for passivation (8% and 10% Cr) was found to exhibit passivity, and was resistant to corrosion in an aqueous 0.6 mol/L NaCl solution whereas coarse-grained Fe-12% Cr, which are known as a stainless steel and passive in most dilute aerated solution, was degraded by corrosion. The findings indicated that the critical threshold of Cr content required for establishing a protective layer by self-passivation in binary Fe-Cr alloy is microstructure dependent, and can be reduced by grain size reduction to a sub-micron scale by SPD. Full article
Figures

Figure 1

Open AccessArticle Effect of Mechanical Activation on the Kinetics of Copper Leaching from Copper Sulfide (CuS)
Metals 2018, 8(3), 150; doi:10.3390/met8030150
Received: 17 December 2017 / Revised: 6 February 2018 / Accepted: 22 February 2018 / Published: 26 February 2018
PDF Full-text (1754 KB) | HTML Full-text | XML Full-text
Abstract
The effect of mechanical activation on the copper leaching of copper sulfide, CuS, in 1 M HNO3 (slurry density: 10 g/L) was investigated by analysis of the leachability and the apparent activation energy. Mechanical activation produced an increase in the leachability and
[...] Read more.
The effect of mechanical activation on the copper leaching of copper sulfide, CuS, in 1 M HNO3 (slurry density: 10 g/L) was investigated by analysis of the leachability and the apparent activation energy. Mechanical activation produced an increase in the leachability and a decrease of the activation energy in this leaching reaction. The leachability increased proportionally to the degree of mechanical activation, reaching 96.6% leaching within 60 min at 80 °C from CuS ground at 700 rpm for 15 min. This leaching process was controlled by surface chemical reaction following the shrinking-core model. The apparent activation energy of leaching for CuS (71.5 kJ/mol) in the range of 50 to 80 °C decreased with an increase of the degree of mechanical activation, reaching 44.3 kJ/mol for Cu leaching from CuS ground at 700 rpm for 15 min. Full article
Figures

Figure 1

Open AccessArticle Investigation of Fracturing and Adhesion Behavior of Hydroxapatite Coating Formed by Aminoacetic Acid-Sodium Aminoacetate Buffer Systems
Metals 2018, 8(3), 151; doi:10.3390/met8030151
Received: 15 January 2018 / Revised: 13 February 2018 / Accepted: 24 February 2018 / Published: 27 February 2018
PDF Full-text (1188 KB) | HTML Full-text | XML Full-text
Abstract
Biomaterials utilized in implantation can be categorized into 4 main categories, as ceramics, polymers, metals and composites. Ceramic-based biomaterials are opted for, particularly in the field of orthopedics. These materials, also named as bioceramics, are usually employed by coating them onto the base
[...] Read more.
Biomaterials utilized in implantation can be categorized into 4 main categories, as ceramics, polymers, metals and composites. Ceramic-based biomaterials are opted for, particularly in the field of orthopedics. These materials, also named as bioceramics, are usually employed by coating them onto the base material, inasmuch as they are far from the mechanical values of bone. In this study, a hydroxyapatite coating that is fully compatible with human blood plasma was applied on Ti6Al4V alloy through a biomimetic technique using aminoacetic acid-sodium aminoacetate buffer system for the first time in the literature, and examinations related thereto were carried out. The surface of the base material Ti6Al4V alloy was activated with various chemicals. Subsequent to activating the surface, a coating process whereby the base material was kept in simulated body fluid for 24, 48, 72, 96 h was carried out. Ultimate microhardness (indentation) tests were performed to determine the average indentation depths in maximum load, vickers hardness and elasticity modulus of the coatings obtained by using the biomimetic method, while scratch tests were performed to measure the surface bonding strengths of the coating layers. Furthermore, the fracture toughness values of the coating were calculated. The results obtained through the study are evaluated and discussed. Full article
Figures

Figure 1

Open AccessArticle Designing a New Ni-Mn-Sn Ferromagnetic Shape Memory Alloy with Excellent Performance by Cu Addition
Metals 2018, 8(3), 152; doi:10.3390/met8030152
Received: 3 February 2018 / Revised: 23 February 2018 / Accepted: 24 February 2018 / Published: 28 February 2018
PDF Full-text (2216 KB) | HTML Full-text | XML Full-text
Abstract
Both magnetic-field-induced reverse martensitic transformation (MFIRMT) and a high working temperature are crucial for the application of Ni-Mn-Sn magnetic shape memory alloys. Here, by first-principles calculations, we demonstrate that the substitution of Cu for Sn is effective not only in enhancing the MFIRMT
[...] Read more.
Both magnetic-field-induced reverse martensitic transformation (MFIRMT) and a high working temperature are crucial for the application of Ni-Mn-Sn magnetic shape memory alloys. Here, by first-principles calculations, we demonstrate that the substitution of Cu for Sn is effective not only in enhancing the MFIRMT but also in increasing martensitic transformation, which is advantageous for its application. Large magnetization difference (ΔM) in Ni-Mn-Sn alloy is achieved by Cu doping, which arises from the enhancement of magnetization of austenite due to the change of Mn-Mn interaction from anti-ferromagnetism to ferromagnetism. This directly leads to the enhancement of MFIRMT. Meanwhile, the martensitic transformation shifts to higher temperature, owing to the energy difference between the austenite L21 structure and the tetragonal martensite L10 structure increases by Cu doping. The results provide the theoretical data and the direction for developing a high temperature magnetic-field-induced shape memory alloy with large ΔM in the Ni-Mn-Sn Heusler alloy system. Full article
Figures

Open AccessFeature PaperArticle The Suitability of Zn–1.3%Fe Alloy as a Biodegradable Implant Material
Metals 2018, 8(3), 153; doi:10.3390/met8030153
Received: 5 February 2018 / Revised: 22 February 2018 / Accepted: 26 February 2018 / Published: 28 February 2018
PDF Full-text (7506 KB) | HTML Full-text | XML Full-text
Abstract
Efforts to develop metallic zinc for biodegradable implants have significantly advanced following an earlier focus on magnesium (Mg) and iron (Fe). Mg and Fe base alloys experience an accelerated corrosion rate and harmful corrosion products, respectively. The corrosion rate of pure Zn, however,
[...] Read more.
Efforts to develop metallic zinc for biodegradable implants have significantly advanced following an earlier focus on magnesium (Mg) and iron (Fe). Mg and Fe base alloys experience an accelerated corrosion rate and harmful corrosion products, respectively. The corrosion rate of pure Zn, however, may need to be modified from its reported ~20 µm/year penetration rate, depending upon the intended application. The present study aimed at evaluating the possibility of using Fe as a relatively cathodic biocompatible alloying element in zinc that can tune the implant degradation rate via microgalvanic effects. The selected Zn–1.3wt %Fe alloy composition produced by gravity casting was examined in vitro and in vivo. The in vitro examination included immersion tests, potentiodynamic polarization and impedance spectroscopy, all in a simulated physiological environment (phosphate-buffered saline, PBS) at 37 °C. For the in vivo study, two cylindrical disks (seven millimeters diameter and two millimeters height) were implanted into the back midline of male Wister rats. The rats were examined post implantation in terms of weight gain and hematological characteristics, including red blood cell (RBC), hemoglobin (HGB) and white blood cell (WBC) levels. Following retrieval, specimens were examined for corrosion rate measurements and histological analysis of subcutaneous tissue in the implant vicinity. In vivo analysis demonstrated that the Zn–1.3%Fe implant avoided harmful systemic effects. The in vivo and in vitro results indicate that the Zn–1.3%Fe alloy corrosion rate is significantly increased compared to pure zinc. The relatively increased degradation of Zn–1.3%Fe was mainly related to microgalvanic effects produced by a secondary Zn11Fe phase. Full article
(This article belongs to the Special Issue Biodegradable Metals)
Figures

Figure 1

Open AccessArticle The Application of 40Ti-35Ni-25Nb Filler Foil in Brazing Commercially Pure Titanium
Metals 2018, 8(3), 154; doi:10.3390/met8030154
Received: 7 February 2018 / Revised: 24 February 2018 / Accepted: 26 February 2018 / Published: 1 March 2018
PDF Full-text (4758 KB) | HTML Full-text | XML Full-text
Abstract
The clad ternary 40Ti-35Ni-25Nb (wt %) foil has been applied in brazing commercially pure titanium (CP-Ti). The wavelength dispersive spectroscope (WDS) was utilized for quantitative chemical analyses of various phases/structures, and electron back scattered diffraction (EBSD) was used for crystallographic analyses in the
[...] Read more.
The clad ternary 40Ti-35Ni-25Nb (wt %) foil has been applied in brazing commercially pure titanium (CP-Ti). The wavelength dispersive spectroscope (WDS) was utilized for quantitative chemical analyses of various phases/structures, and electron back scattered diffraction (EBSD) was used for crystallographic analyses in the brazed joint. The microstructure of brazed joint relies on the Nb and Ni distributions across the joint. For the β-Ti alloyed with high Nb and low Ni contents, the brazed zone (BZ), consisting of the stabilized β-Ti at room temperature. In contrast, eutectoid decomposition of the β-Ti into Ti2Ni and α-Ti is widely observed in the transition zone (TZ) of the joint. Although average shear strengths of joints brazed at different temperatures are approximately the same level, their standard deviations decreased with increasing the brazing temperature. The presence of inherent brittle Ti2Ni intermetallics results in higher standard deviation in shear test. Because the Ni content is lowered in TZ at a higher brazing temperature, the amount of eutectoid is decreased in TZ. The fracture location is changed from TZ into BZ mixed with α and β-Ti. Full article
(This article belongs to the Special Issue Science, Characterization and Technology of Joining and Welding)
Figures

Open AccessArticle The Influence of Cu Addition on Dispersoid Formation and Mechanical Properties of Al-Mn-Mg 3004 Alloy
Metals 2018, 8(3), 155; doi:10.3390/met8030155
Received: 30 January 2018 / Revised: 23 February 2018 / Accepted: 27 February 2018 / Published: 2 March 2018
PDF Full-text (7448 KB) | HTML Full-text | XML Full-text
Abstract
The effect of Cu addition on dispersoid precipitation, mechanical properties and creep resistance was investigated in an Al-Mn-Mg 3004 alloy. The addition of Cu promoted dispersoid precipitation by increasing the number density and decreasing the size of dispersoids. Metastable β′-Mg2Si and
[...] Read more.
The effect of Cu addition on dispersoid precipitation, mechanical properties and creep resistance was investigated in an Al-Mn-Mg 3004 alloy. The addition of Cu promoted dispersoid precipitation by increasing the number density and decreasing the size of dispersoids. Metastable β′-Mg2Si and Q-AlCuMgSi precipitates were observed during the heating process and both could provide favorable nucleation sites for dispersoid precipitation. The addition of Cu improved the thermal stability of dispersoids during a long-term thermal holding at 350 °C for 500 h. Results of mechanical testing show that the addition of Cu remarkably improved the hardness at room temperature, as well as the yield strength and creep resistance at 300 °C, which was mainly attributed to dispersoid strengthening and Cu solid solution strengthening. The yield strength contribution at 300 °C was quantitatively evaluated based on the dispersoid, solid solution and matrix contributions. It was confirmed that dispersoid strengthening is the main strengthening mechanism in the experimental alloys. Full article
Figures

Figure 1

Open AccessArticle Characterization of a New Microstructure in a β-Solidifying TiAl Alloy after Air-Cooling from a β Phase Field and Subsequent Tempering
Metals 2018, 8(3), 156; doi:10.3390/met8030156
Received: 12 February 2018 / Revised: 27 February 2018 / Accepted: 28 February 2018 / Published: 2 March 2018
PDF Full-text (7088 KB) | HTML Full-text | XML Full-text
Abstract
In this study, we found that well-developed α2′ martensite was formed in a Ti-40Al-10V (atomic percent or at.%) alloy after air-cooling from a β phase field, rather than the traditional α2/γ lamellar colonies. The martensitic laths were produced according
[...] Read more.
In this study, we found that well-developed α2′ martensite was formed in a Ti-40Al-10V (atomic percent or at.%) alloy after air-cooling from a β phase field, rather than the traditional α2/γ lamellar colonies. The martensitic laths were produced according to the Burgers orientation relationship (OR), the same as those during quenching. Local variant selection detected that three (or six) α2′ variants sharing one (or two) common [11.0]α2′ axes were predominant, while no global variant selection was observed. Subsequent to the martensitic transformation, the retained β phase was decomposed mainly via a β→γ transformation. The γ laths always nucleated at the α2′/β interface according to a Blackburn orientation relationship. In order to stabilize the microstructure, the air-cooled samples were tempered at 800–1000 °C. During tempering, the microstructure decomposed mainly via an α2′→γ transformation. The martensite was almost completely transformed after tempering at 1000 °C for 4 h, and hence a fine β-γ microstructure was obtained. Such a treatment resembling the quenching–tempering in steels may be a new strategy for the microstructural design of TiAl alloys, while an unexpected quenching process can be avoided. Full article
Figures

Figure 1

Open AccessArticle A Fragmentation Criterion for the Interface of a Hydrostatic Extruded Al-Mg-Compound
Metals 2018, 8(3), 157; doi:10.3390/met8030157
Received: 15 December 2017 / Revised: 8 February 2018 / Accepted: 21 February 2018 / Published: 2 March 2018
Cited by 1 | PDF Full-text (3984 KB) | HTML Full-text | XML Full-text
Abstract
Due to the higher demand for energy efficient products, light-weight constructions have become more important in recent years. An innovative, hydrostatic extruded Al-Mg-compound used here combines the corrosion resistance of aluminium with the outstanding lightweight properties of magnesium. During the production process, a
[...] Read more.
Due to the higher demand for energy efficient products, light-weight constructions have become more important in recent years. An innovative, hydrostatic extruded Al-Mg-compound used here combines the corrosion resistance of aluminium with the outstanding lightweight properties of magnesium. During the production process, a thin boundary layer is built between the two basic materials. Investigations on further hot forming processing revealed a good formability of these compounds despite the fact that the boundary layer splits into fragments during forging and a new secondary boundary layer is built when the basic materials between the fragments come into contact again during the continuous deformation. The aim of the research is now to investigate fragmentation depending on the deformation rate and boundary layer thickness, which increases during the heat-up process in preparation of forging. For this purpose, a channel compression test is used in conjunction with a special newly developed specimen shape. The metallographic evaluation of the boundary layer reveals a strong dependency of fragmentation on the deformation rate and the boundary layer thickness. With the aid of a numerical simulation, an individual critical stretch could be determined at which fragmentation starts, and provide guidance for an optimal forging process design. Full article
Figures

Figure 1

Open AccessArticle Effect of Hot Mill Scale on Hydrogen Embrittlement of High Strength Steels for Pre-Stressed Concrete Structures
Metals 2018, 8(3), 158; doi:10.3390/met8030158
Received: 2 February 2018 / Revised: 23 February 2018 / Accepted: 23 February 2018 / Published: 3 March 2018
PDF Full-text (9475 KB) | HTML Full-text | XML Full-text
Abstract
The presence of a conductive layers of hot-formed oxide on the surface of bars for pre or post-compressing structures can promote localized attacks as a function of pH. The aggressive local environment in the occluded cells inside localized attacks has as consequence the
[...] Read more.
The presence of a conductive layers of hot-formed oxide on the surface of bars for pre or post-compressing structures can promote localized attacks as a function of pH. The aggressive local environment in the occluded cells inside localized attacks has as consequence the possibility of initiation of stress corrosion cracking. In this paper, the stress corrosion cracking behavior of high strength steels proposed for tendons was studied by means of Constant Load (CL) tests and Slow Strain Rate (SSR) tests. Critical ranges of pH for cracking were verified. The promoting role of localized attack was confirmed. Further, electrochemical tests were performed on bars in as received surface conditions, in order to evaluate pitting initiation. The adverse effect of mill scale was recognized. Full article
(This article belongs to the Special Issue Mechanical Behavior of High-Strength Low-Alloy Steels)
Figures

Figure 1

Open AccessArticle Interface Characteristic of Explosive-Welded and Hot-Rolled TA1/X65 Bimetallic Plate
Metals 2018, 8(3), 159; doi:10.3390/met8030159
Received: 30 December 2017 / Revised: 28 February 2018 / Accepted: 1 March 2018 / Published: 4 March 2018
PDF Full-text (6234 KB) | HTML Full-text | XML Full-text
Abstract
TA1/X65 bimetallic plate has a bright future of application by combining the excellent corrosion resistance of TA1 and the high strength of inexpensive X65 steel, while manufacturing large size TA1/X65 bimetallic plate is still a challenging task. Multi-pass hot-rolling is the most common
[...] Read more.
TA1/X65 bimetallic plate has a bright future of application by combining the excellent corrosion resistance of TA1 and the high strength of inexpensive X65 steel, while manufacturing large size TA1/X65 bimetallic plate is still a challenging task. Multi-pass hot-rolling is the most common way to achieve a large size bimetallic plate. In this work, interface characteristic of explosive-welded and multi-pass hot-rolled TA1/X65 bimetallic plate is experimentally studied. The microstructure, composition and microhardness distribution across the TA1/X65 interface are investigated by optical metallographic observation, scanning electron microscope (SEM) observation, energy dispersive spectrometer (EDS) analysis, and Vickers hardness test. Shear tests and stratified tensile tests are conducted with emphasis on impacts of the angle between loading direction and detonation wave propagation direction on interface strength. A straight TA1/X65 interface with periodic morphology of residual peninsula could be observed on the cross section parallel to detonation wave propagation direction, while in most cases there is no residual peninsula morphology on the straight TA1/X65 interface when the cross section is perpendicular to detonation wave propagation direction. TA1/X65 interface of explosive-welded and multi-pass hot-rolled bimetallic plate presents higher bearing capacity for the load perpendicular to detonation wave propagation direction than that for the load parallel to detonation wave propagation direction. The results of this paper have a certain guiding significance for the fabrication of pipes and containers made of explosive-welded and hot-rolled TA1/X65 bimetallic plate. Full article
(This article belongs to the Special Issue Laser Welding of Industrial Metal Alloys)
Figures

Open AccessArticle Characterization on the Microstructure Evolution and Toughness of TIG Weld Metal of 25Cr2Ni2MoV Steel after Post Weld Heat Treatment
Metals 2018, 8(3), 160; doi:10.3390/met8030160
Received: 16 January 2018 / Revised: 26 February 2018 / Accepted: 3 March 2018 / Published: 6 March 2018
PDF Full-text (10383 KB) | HTML Full-text | XML Full-text
Abstract
The microstructure and toughness of tungsten inert gas (TIG) backing weld parts in low-pressure steam turbine welded rotors contribute significantly to the total toughness of the weld metal. In this study, the microstructure evolution and toughness of TIG weld metal of 25Cr2Ni2MoV steel
[...] Read more.
The microstructure and toughness of tungsten inert gas (TIG) backing weld parts in low-pressure steam turbine welded rotors contribute significantly to the total toughness of the weld metal. In this study, the microstructure evolution and toughness of TIG weld metal of 25Cr2Ni2MoV steel low-pressure steam turbine welded rotor under different post-weld heat treatment (PWHT) conditions are investigated. The fractography and microstructure of weld metal after PWHT are characterized by optical microscope, SEM, and TEM, respectively. The Charpy impact test is carried out to evaluate the toughness of the weld. The optical microscope and SEM results indicate that the as-welded sample is composed of granular bainite, acicular ferrite and blocky martensite/austenite (M-A) constituent. After PWHT at 580 °C, the blocky M-A decomposes into ferrite and carbides. Both the number and size of precipitated carbides increase with holding time. The impact test results show that the toughness decreases dramatically after PWHT and further decreases with holding time at 580 °C. The precipitated carbides are identified as M23C6 carbides by TEM, which leads to the dramatic decrease in the toughness of TIG weld metal of 25Cr2Ni2MoV steel. Full article
Figures

Figure 1

Open AccessArticle Automated Method for Fractographic Analysis of Shape and Size of Dimples on Fracture Surface of High-Strength Titanium Alloys
Metals 2018, 8(3), 161; doi:10.3390/met8030161
Received: 23 January 2018 / Revised: 18 February 2018 / Accepted: 2 March 2018 / Published: 6 March 2018
PDF Full-text (8470 KB) | HTML Full-text | XML Full-text
Abstract
An automated method for analyzing the shape and size of dimples of ductile tearing formed during static and impact fracture of titanium alloys VT23 and VT23M is proposed. The method is based on the analysis of the image topology. The method contains the
[...] Read more.
An automated method for analyzing the shape and size of dimples of ductile tearing formed during static and impact fracture of titanium alloys VT23 and VT23M is proposed. The method is based on the analysis of the image topology. The method contains the operations of smoothing the initial fractographic image; its convolution with a filter to identify the topological ridges; thresholding with subsequent skeletonization to identify boundaries between dimples; clustering to isolate the connected areas that represent the sought objects—dimples. For each dimple, the following quantitative characteristics were calculated: area, coefficient of roundness and visual depth in units of image intensity. The surface of ductile tearing was studied by analyzing the peculiarities of parameter distribution of the found dimples. The proposed method is applied to fractograms of fracture surfaces of titanium alloys VT23 and VT23M. Full article
Figures

Open AccessArticle Anodic Lodes and Scrapings as a Source of Electrolytic Manganese
Metals 2018, 8(3), 162; doi:10.3390/met8030162
Received: 26 December 2017 / Revised: 23 February 2018 / Accepted: 1 March 2018 / Published: 7 March 2018
PDF Full-text (3344 KB) | HTML Full-text | XML Full-text
Abstract
Manganese is an element of interest in metallurgy, especially in ironmaking and steel making, but also in copper and aluminum industries. The depletion of manganese high grade sources and the environmental awareness have led to search for new manganese sources, such as wastes/by-products
[...] Read more.
Manganese is an element of interest in metallurgy, especially in ironmaking and steel making, but also in copper and aluminum industries. The depletion of manganese high grade sources and the environmental awareness have led to search for new manganese sources, such as wastes/by-products of other metallurgies. In this way, we propose the recovery of manganese from anodic lodes and scrapings of the zinc electrolysis process because of their high Mn content (>30%). The proposed process is based on a mixed leaching: a lixiviation-neutralization at low temperature (50 °C, reached due to the exothermic reactions involved in the process) and a lixiviation with sulfuric acid at high temperature (150–200 °C, in heated reactor). The obtained solution after the combined process is mainly composed by manganese sulphate. This solution is then neutralized with CaO (or manganese carbonate) as a first purification stage, removing H2SO4 and those impurities that are easily removable by controlling pH. Then, the purification of nobler elements than manganese is performed by their precipitation as sulphides. The purified solution is sent to electrolysis where electrolytic manganese is obtained (99.9% Mn). The versatility of the proposed process allows for obtaining electrolytic manganese, oxide of manganese (IV), oxide of manganese (II), or manganese sulphate. Full article
Figures

Open AccessArticle Metal Injection Moulding of High Nb-Containing TiAl Alloy and Its Oxidation Behaviour at 900 °C
Metals 2018, 8(3), 163; doi:10.3390/met8030163
Received: 4 February 2018 / Revised: 25 February 2018 / Accepted: 3 March 2018 / Published: 7 March 2018
PDF Full-text (16668 KB) | HTML Full-text | XML Full-text
Abstract
High Nb-containing TiAl alloy with a nominal composition of Ti-45Al-8.5Nb-0.2W-0.2B-0.02Y (at %) was fabricated by metal injection moulding (MIM) technology with an improved wax-based binder. The critical powder loading and feedstock rheological behaviour were determined. The influence of sintering temperature on microstructures and
[...] Read more.
High Nb-containing TiAl alloy with a nominal composition of Ti-45Al-8.5Nb-0.2W-0.2B-0.02Y (at %) was fabricated by metal injection moulding (MIM) technology with an improved wax-based binder. The critical powder loading and feedstock rheological behaviour were determined. The influence of sintering temperature on microstructures and mechanical properties of the sintered samples and their oxidation behaviour were also investigated. Results showed that a feedstock, with a powder loading of 68 vol % and good flowability, could be obtained by using the improved binder, and oxygen pick-up was lower than that of the sample prepared by using a traditional binder. The ultimate tensile strength (UTS) and plastic elongation of the sample sintered at 1480 °C for 2 h were 412 MPa and 0.33%, at room temperature, respectively. The 1480 °C-sintered sample consisted of γ/α2 lamellar microstructure with the average colony size of about 70 µm, and its porosity was about 4%. The sintered alloy showed better oxidation resistance than that of the cast alloy counterpart. Full article
(This article belongs to the Special Issue Powder Synthesis and Processing)
Figures

Open AccessArticle In Vitro Corrosion Assessment of Additively Manufactured Porous NiTi Structures for Bone Fixation Applications
Metals 2018, 8(3), 164; doi:10.3390/met8030164
Received: 14 January 2018 / Revised: 1 March 2018 / Accepted: 6 March 2018 / Published: 8 March 2018
PDF Full-text (5658 KB) | HTML Full-text | XML Full-text
Abstract
NiTi alloys possess distinct functional properties (i.e., shape memory effect and superelasticity) and biocompatibility, making them appealing for bone fixation applications. Additive manufacturing offers an alternative method for fabricating NiTi parts, which are known to be very difficult to machine using conventional manufacturing
[...] Read more.
NiTi alloys possess distinct functional properties (i.e., shape memory effect and superelasticity) and biocompatibility, making them appealing for bone fixation applications. Additive manufacturing offers an alternative method for fabricating NiTi parts, which are known to be very difficult to machine using conventional manufacturing methods. However, poor surface quality, and the presence of impurities and defects, are some of the major concerns associated with NiTi structures manufactured using additive manufacturing. The aim of this study is to assess the in vitro corrosion properties of additively manufactured NiTi structures. NiTi samples (bulk and porous) were produced using selective laser melting (SLM), and their electrochemical corrosion characteristics and Ni ion release levels were measured and compared with conventionally fabricated NiTi parts. The additively manufactured NiTi structures were found to have electrochemical corrosion characteristics similar to those found for the conventionally fabricated NiTi alloy samples. The highest Ni ion release level was found in the case of 50% porous structures, which can be attributed to their significantly higher exposed surface area. However, the Ni ion release levels reported in this work for all the fabricated structures remain within the range of most of values for conventionally fabricated NiTi alloys reported in the literature. The results of this study suggest that the proposed SLM fabrication process does not result in a significant deterioration in the corrosion resistance of NiTi parts, making them suitable for bone fixation applications. Full article
(This article belongs to the Special Issue Failure Analysis of Biometals)
Figures

Figure 1

Open AccessArticle A Comparative Study of Corrosion Behavior of Hard Anodized and Micro-Arc Oxidation Coatings on 7050 Aluminum Alloy
Metals 2018, 8(3), 165; doi:10.3390/met8030165
Received: 19 January 2018 / Revised: 23 February 2018 / Accepted: 7 March 2018 / Published: 8 March 2018
PDF Full-text (8171 KB) | HTML Full-text | XML Full-text
Abstract
Two kinds of metal oxide coatings were fabricated on 7050 Al alloy by hard anodization (HA) and micro-arc oxidation (MAO) techniques. The microstructure, phase composition, and corrosion behavior of the two coatings were studied by scanning electron microscopy, X-ray diffraction, and corrosion tests,
[...] Read more.
Two kinds of metal oxide coatings were fabricated on 7050 Al alloy by hard anodization (HA) and micro-arc oxidation (MAO) techniques. The microstructure, phase composition, and corrosion behavior of the two coatings were studied by scanning electron microscopy, X-ray diffraction, and corrosion tests, respectively. When compared with the HA coating, the MAO one was more effective to isolate the substrate from the corrosive environment. In addition, as confirmed by electrochemical tests, the MAO coating was of better corrosion resistance than the HA coating. Furthermore, it was revealed by neutral salt spray test that the MAO coating could protect substrate alloy over 1140 h, while the HA coating can only protect substrate alloy for 46 h due to the amorphous composition and through thickness defects (micro-pores and micro-cracks). Full article
Figures

Figure 1

Open AccessArticle Arc Brazing of Aluminium, Aluminium Matrix Composites and Stainless Steel in Dissimilar Joints
Metals 2018, 8(3), 166; doi:10.3390/met8030166
Received: 30 January 2018 / Revised: 2 March 2018 / Accepted: 5 March 2018 / Published: 8 March 2018
Cited by 1 | PDF Full-text (28008 KB) | HTML Full-text | XML Full-text
Abstract
The publication describes the approaches and results of the investigation of arc brazing processes to produce dissimilar joints of particle reinforced aluminium matrix composites (AMC) to aluminium alloys and steels. Arc brazing allows for low thermal energy input to the joint parts, and
[...] Read more.
The publication describes the approaches and results of the investigation of arc brazing processes to produce dissimilar joints of particle reinforced aluminium matrix composites (AMC) to aluminium alloys and steels. Arc brazing allows for low thermal energy input to the joint parts, and is hence suitable to be applied to AMC. In addition, a braze filler B-Al40Ag40Cu20 alloyed with Si with a liquidus temperature of below 500 °C is selected to further reduce the thermal energy input during joining. The microstructures of the joining zones were analysed by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDXS), and X-ray diffraction analysis (XRD), as well as their hardness profile characterised and discussed. Joint strengths were measured by tensile shear tests, and resulting areas of fracture were discussed in accordance to the joints’ microstructures and gained bond strength values. Full article
Figures

Figure 1

Open AccessArticle Compound Formation and Microstructure of As-Cast High Entropy Aluminums
Metals 2018, 8(3), 167; doi:10.3390/met8030167
Received: 8 February 2018 / Revised: 2 March 2018 / Accepted: 6 March 2018 / Published: 9 March 2018
PDF Full-text (3987 KB) | HTML Full-text | XML Full-text
Abstract
The aim of this work is to study the microstructure of four high entropy alloys (HEAs) produced by large scale vacuum die casting. Al40Cu15Mn5Ni5Si20Zn15, Al45Cu15Mn5Fe
[...] Read more.
The aim of this work is to study the microstructure of four high entropy alloys (HEAs) produced by large scale vacuum die casting. Al40Cu15Mn5Ni5Si20Zn15, Al45Cu15Mn5Fe5Si5Ti5Zn20, Al35Cu5Fe5Mn5Si30V10Zr10, and Al50Ca5Cu5Ni10Si20Ti10 alloys formed a mixture of different structures, containing intermetallic compound (IC) and solid solution (SS) phases. The phases observed in the casting alloys were compared with the equilibrium phases predicted by Thermo-Calc. The measured densities varied from 3.33 g/cm−3 to 5.07 g/cm−3 and microhardness from 437 Hv to 887 Hv. Thus, the microhardness and estimated strength/density ratios are significantly higher than other lightweight high entropy alloys (LWHEAs). Full article
(This article belongs to the Special Issue Microstructure and Mechanical Properties of Casting Alloys)
Figures

Figure 1

Open AccessArticle Precipitation and Grain Size Effects on the Tensile Strain-Hardening Exponents of an API X80 Steel Pipe after High-Frequency Hot-Induction Bending
Metals 2018, 8(3), 168; doi:10.3390/met8030168
Received: 30 November 2017 / Revised: 21 February 2018 / Accepted: 24 February 2018 / Published: 9 March 2018
PDF Full-text (3567 KB) | HTML Full-text | XML Full-text
Abstract
This study discusses the use of the Morrison model to estimate the strain-hardening exponent (n) in the presence of precipitation hardening for an API X80 steel pipe. As the grain size becomes larger, high values of n are expected according to
[...] Read more.
This study discusses the use of the Morrison model to estimate the strain-hardening exponent (n) in the presence of precipitation hardening for an API X80 steel pipe. As the grain size becomes larger, high values of n are expected according to the Morrison equation. However, the grain size alone is not sufficient to explain the changes of the strain-hardening exponent (n) after hot-induction bending. The vanadium in the ferritic solid solution has an important influence on the decrease of the precipitation hardening, and consequently on the increase of the values of n, despite the refinement of the grain size and high dislocation densities. Therefore, the effects of grain boundaries on the capability to uniformly distribute deformations within the plastic regime become negligible, which limits the application of the Morrison model to estimate the values of n. Full article
(This article belongs to the Special Issue Mechanical Behavior of High-Strength Low-Alloy Steels)
Figures

Figure 1

Open AccessArticle Assessment of Steel Subjected to the Thermomechanical Control Process with Respect to Weldability
Metals 2018, 8(3), 169; doi:10.3390/met8030169
Received: 24 January 2018 / Revised: 1 March 2018 / Accepted: 7 March 2018 / Published: 9 March 2018
PDF Full-text (8707 KB) | HTML Full-text | XML Full-text
Abstract
The study is concerned with the assessment of the weldability of steel S700MC subjected to the thermomechanical control process (TMCP) and precipitation hardening and characterised by a high yield point. Appropriate mechanical and plastic properties of steel S700MC were obtained using the thermomechanical
[...] Read more.
The study is concerned with the assessment of the weldability of steel S700MC subjected to the thermomechanical control process (TMCP) and precipitation hardening and characterised by a high yield point. Appropriate mechanical and plastic properties of steel S700MC were obtained using the thermomechanical control process through precipitation, solution, and strain hardening as well as by using grain-refinement-related processes. Constituents responsible for the hardening of steel S700MC include Ti, Nb, N, and C. The hardening is primarily affected by (Ti,Nb)(C,N)-type dispersive precipitates sized from several nanometres to between ten and twenty nanometres. The welding process considerably differs from TMCP conditions, leading to the reduction of plastic properties both in the heat-affected zone (HAZ) and in the weld area. This study demonstrates that in cases of TMCP steels, where the effect of precipitation hardening is obtained through titanium and niobium hardening phases, the carbon equivalent and phase transformation γ–α cannot constitute the basis of weldability assessment. The properties of welded joints made from the above-named group of steels are primarily affected by the stability of hardening phases, changes in their dispersion, and ageing processes. The most inferior properties were identified in the high-temperature and coarse-grained HAZ area, where the nucleation of hardening phases in the matrix and their uncontrolled reprecipitation in the fine-dispersive form lead to a sharp decrease in toughness. Full article
(This article belongs to the Special Issue Researches and Simulations in Steel Rolling)
Figures

Figure 1

Open AccessArticle Microstructural Characteristics and m23c6 Precipitate Behavior of the Course-Grained Heat-Affected Zone of T23 Steel without Post-Weld Heat Treatment
Metals 2018, 8(3), 170; doi:10.3390/met8030170
Received: 10 December 2017 / Revised: 28 February 2018 / Accepted: 8 March 2018 / Published: 9 March 2018
PDF Full-text (9634 KB) | HTML Full-text | XML Full-text
Abstract
The microstructural characteristics of a simulated heat-affected zone (HAZ) in SA213-T23 (2.25Cr-1.6W steel) used for boiler tubes employed in thermal power plants were investigated using nital, alkaline sodium picrate, and Murakami’s etchants. In order to investigate the microstructure formation process of the HAZ
[...] Read more.
The microstructural characteristics of a simulated heat-affected zone (HAZ) in SA213-T23 (2.25Cr-1.6W steel) used for boiler tubes employed in thermal power plants were investigated using nital, alkaline sodium picrate, and Murakami’s etchants. In order to investigate the microstructure formation process of the HAZ in the welding process, simulated HAZ specimens were fabricated at intervals of 100 °C for peak temperatures between 950 and 1350 °C, and the microstructural features and precipitate behavior at various peak temperatures were observed. The alkaline-sodium-picrate-etched microstructures exhibited a black dot or band, which was not observed in the natal-etched microstructure. As the temperature increased from 950 to 1350 °C, the black dot and band became wider and thicker. Experimental analyses using an electron probe micro-analyzer, electron backscatter diffraction, and transmission electron microscopy revealed the appearance of austenite in the black dot region at a peak temperature of 950 °C; its amount increased up to a peak temperature of 1050 °C and thereafter decreased as the peak temperature further increased. The amount of M23C6 decreased with an increase in peak temperature. Based on these results, we investigated the behaviors of austenite and M23C6 as functions of the peak temperature. Full article
(This article belongs to the Special Issue Science, Characterization and Technology of Joining and Welding)
Figures

Open AccessArticle Short-Cut Method to Assess a Gross Available Energy in a Medium-Load Screw Friction Press
Metals 2018, 8(3), 173; doi:10.3390/met8030173
Received: 3 January 2018 / Revised: 8 February 2018 / Accepted: 9 March 2018 / Published: 10 March 2018
PDF Full-text (2232 KB) | HTML Full-text | XML Full-text
Abstract
The present study proposed a rapid method, based on a previous universal compression tests, to estimate the required load capacity to cold forge different specimen quantity in a screw press. Accordingly, experimental and theoretical approach are performed to check new adjustable drive motor
[...] Read more.
The present study proposed a rapid method, based on a previous universal compression tests, to estimate the required load capacity to cold forge different specimen quantity in a screw press. Accordingly, experimental and theoretical approach are performed to check new adjustable drive motor of the modified forging machine to achieve a gross available energy to deform the specimens preventing damage of the forging machine. During the forging experiments, two screw friction presses (as-received and modified) are used to validate the theoretical approach. The modified press exhibits an increase of 51% of gross energy and 11% of maximum load capacity compare to the as-received press. This method is used to improve the effective of the forging process avoiding excessive loads that could promote machine failure. Therefore, a low-cost and easy to implement methodology is proposed to determine the energy and load capacity of a screw friction press to forge different specimen quantities with symmetry pattern configurations. Full article
Figures

Open AccessArticle Scaling Law in Laser-Induced Shock Effects of NiTi Shape Memory Alloy
Metals 2018, 8(3), 174; doi:10.3390/met8030174
Received: 29 January 2018 / Revised: 3 March 2018 / Accepted: 6 March 2018 / Published: 10 March 2018
PDF Full-text (4880 KB) | HTML Full-text | XML Full-text
Abstract
The shock effects in laser shock processing of NiTi shape memory alloy were studied by dimensional analysis and finite element simulation. The essential dimensionless parameters controlling the residual stress distribution and plastically affected depth were found to be dimensionless pressure duration and peak
[...] Read more.
The shock effects in laser shock processing of NiTi shape memory alloy were studied by dimensional analysis and finite element simulation. The essential dimensionless parameters controlling the residual stress distribution and plastically affected depth were found to be dimensionless pressure duration and peak pressure. By adopting the constitutive model considering the martensitic transformation and plasticity of deformation induced martensite, the influence of dimensionless parameters on the shock effects of shape memory alloy was studied numerically. The numerical results reveal the scaling law of shock effects on those dimensionless parameters quantitatively and the relationship between the plastically affected depth and peak pressure was validated with experimental results. A window of the optimal processing parameters could be obtained based on this study. Full article
Figures

Figure 1

Open AccessArticle Development and Characterisation of Aluminium Matrix Nanocomposites AlSi10Mg/MgAl2O4 by Laser Powder Bed Fusion
Metals 2018, 8(3), 175; doi:10.3390/met8030175
Received: 19 February 2018 / Revised: 4 March 2018 / Accepted: 7 March 2018 / Published: 10 March 2018
PDF Full-text (6523 KB) | HTML Full-text | XML Full-text
Abstract
Recently, additive manufacturing techniques have been gaining attention for the fabrication of parts from aluminium alloys to composites. In this work, the processing of an AlSi10Mg based composite reinforced with 0.5% in weight of MgAl2O4 nanoparticles through laser powder bed
[...] Read more.
Recently, additive manufacturing techniques have been gaining attention for the fabrication of parts from aluminium alloys to composites. In this work, the processing of an AlSi10Mg based composite reinforced with 0.5% in weight of MgAl2O4 nanoparticles through laser powder bed fusion (LPBF) process is presented. After an initial investigation about the effect of process parameters on the densification levels, the LPBF materials were analysed in terms of microstructure, thermo-mechanical and mechanical properties. The presence of MgAl2O4 nanoparticles involves an increment of the volumetric energy density delivered to the materials, in order to fabricate samples with high densification levels similar to the AlSi10Mg samples. However, the application of different building parameters results in modifying the size of the cellular structures influencing the mechanical properties and therefore, limiting the strengthening effect of the reinforcement. Full article
(This article belongs to the Special Issue Production and Properties of Light Metal Matrix Nanocomposites)
Figures

Open AccessArticle Agglomeration Behavior of Non-Metallic Particles on the Surface of Ca-Treated High-Carbon Liquid Steel: An In Situ Investigation
Metals 2018, 8(3), 176; doi:10.3390/met8030176
Received: 2 December 2017 / Revised: 9 March 2018 / Accepted: 10 March 2018 / Published: 12 March 2018
PDF Full-text (7263 KB) | HTML Full-text | XML Full-text
Abstract
The agglomeration behavior of non-metallic inclusion is a critical phenomenon that needs to be controlled as it has a direct relationship with the performance of produced steel. Although the agglomerates can be potential points for serious defects in every grade of steel, they
[...] Read more.
The agglomeration behavior of non-metallic inclusion is a critical phenomenon that needs to be controlled as it has a direct relationship with the performance of produced steel. Although the agglomerates can be potential points for serious defects in every grade of steel, they are likely to be more serious in high-carbon steel due to the low ductility of these grades of steels as well as their usage in severe conditions. Confocal scanning laser microscopes (CSLM) have been used by different researchers to investigate the agglomeration behavior of non-metallic particles at the interface of liquid steel and Ar gas, in situ. In recent decades, the agglomeration of Al2O3 particle in and on the surface of low-carbon steel has been widely investigated. However, there are very few studies focussing on non-Al2O3 inclusions which are included in a Ca-treated high-carbon steel. In this study, the agglomeration behaviors of sulfide/sulfide and sulfide/oxide particles on the surface of liquid high-carbon steel have been investigated in detail using CSLM. Agglomerations on the liquid surface are governed by capillary forces similar to the Al2O3 particle but this study demonstrates that agglomeration forces among non-Al2O3 particles on the surface of re-melted high-carbon samples are lower than pure-Al2O3 on the surface of low-carbon steel. Despite this, they show similar or longer acting lengths than pure-Al2O3. Full article
Figures

Figure 1

Open AccessArticle Low-Waste Recycling of Spent CuO-ZnO-Al2O3 Catalysts
Metals 2018, 8(3), 177; doi:10.3390/met8030177
Received: 22 January 2018 / Revised: 5 March 2018 / Accepted: 7 March 2018 / Published: 12 March 2018
PDF Full-text (1282 KB) | HTML Full-text | XML Full-text
Abstract
CuO-ZnO-Al2O3 catalysts are designed for low-temperature conversion in the process of hydrogen and ammonia synthesis gas production. This paper presents the results of research into the recovery of copper and zinc from spent catalysts using pyrometallurgical and hydrometallurgical methods. Under
[...] Read more.
CuO-ZnO-Al2O3 catalysts are designed for low-temperature conversion in the process of hydrogen and ammonia synthesis gas production. This paper presents the results of research into the recovery of copper and zinc from spent catalysts using pyrometallurgical and hydrometallurgical methods. Under reducing conditions, at high temperature, having appropriately selected the composition of the slag, more than 66% of the copper can be extracted in metallic form, and about 70% of zinc in the form of ZnO from this material. Hydrometallurgical processing of the catalysts was carried out using two leaching solutions: alkaline and acidic. Almost 62% of the zinc contained in the catalysts was leached to the alkaline solution, and about 98% of the copper was leached to the acidic solution. After the hydrometallurgical treatment of the catalysts, an insoluble residue was also obtained in the form of pure ZnAl2O4. This compound can be reused to produce catalysts, or it can be processed under reducing conditions at high temperature to recover zinc. The recovery of zinc and copper from such a material is consistent with the policy of sustainable development, and helps to reduce the environmental load of stored wastes. Full article
Figures

Figure 1

Open AccessFeature PaperArticle Effect of Carbon Content on the Microstructure and Mechanical Properties of NbC-Ni Based Cermets
Metals 2018, 8(3), 178; doi:10.3390/met8030178
Received: 11 January 2018 / Revised: 21 February 2018 / Accepted: 6 March 2018 / Published: 12 March 2018
PDF Full-text (30371 KB) | HTML Full-text | XML Full-text
Abstract
The aim of this work was to correlate the overall carbon content in NbC-Ni, NbC-Ni-VC and NbC-Ni-Mo starting powders with the resulting microstructure, hardness, and fracture toughness of Ni-bonded NbC cermets. A series of NbC-Ni, NbC-Ni-VC and NbC-Ni-Mo cermets with different carbon content
[...] Read more.
The aim of this work was to correlate the overall carbon content in NbC-Ni, NbC-Ni-VC and NbC-Ni-Mo starting powders with the resulting microstructure, hardness, and fracture toughness of Ni-bonded NbC cermets. A series of NbC-Ni, NbC-Ni-VC and NbC-Ni-Mo cermets with different carbon content were prepared by conventional liquid phase sintering for 1 h at 1420 °C in vacuum. Microstructural analysis of the fully densified cermets was performed by electron probe microanalysis (EPMA) to assess the effect of carbon and VC or Mo additions on the NbC grain growth and morphology. A decreased carbon content in the starting powder mixtures resulted in increased dissolution of Nb, V, and Mo in the Ni binder and a decreased C/Nb ratio in the NbC based carbide phase. The Vickers hardness (HV30) and Palmqvist indentation toughness were found to decrease significantly with an increasing carbon content in the Mo-free cermets, whereas an antagonistic correlation between hardness and toughness was obtained as a function of the Mo-content in Mo-modified NbC cermets. To obtain optimized mechanical properties, methods to control the total carbon content of NbC-Ni mixtures were proposed and the prepared cermets were investigated in detail. Full article
(This article belongs to the Special Issue Cermets and Hardmetals)
Figures

Open AccessArticle A Correlation between the Ultimate Shear Stress and the Thickness Affected by Intermetallic Compounds in Friction Stir Welding of Dissimilar Aluminum Alloy–Stainless Steel Joints
Metals 2018, 8(3), 179; doi:10.3390/met8030179
Received: 19 February 2018 / Revised: 6 March 2018 / Accepted: 9 March 2018 / Published: 13 March 2018
PDF Full-text (16765 KB) | HTML Full-text | XML Full-text
Abstract
In this work, Friction Stir Welding (FSW) was applied to join a stainless steel 316L and an aluminum alloy 5083. Ranges of rotation and translation speeds of the tool were used to obtain welding samples with different heat input coefficients. Depending on the
[...] Read more.
In this work, Friction Stir Welding (FSW) was applied to join a stainless steel 316L and an aluminum alloy 5083. Ranges of rotation and translation speeds of the tool were used to obtain welding samples with different heat input coefficients. Depending on the process parameters, the heat generated by FSW creates thin layers of Al-rich InterMetallic Compound (IMC) mainly composed of FeAl3, identified by energy dispersive spectrometry. Traces of Fe2Al5 were also depicted in some samples by X-ray diffraction analysis and transmission electron microscopy. Monotonous tensile tests performed on the weld joint show the existence of a maximum mechanical resistance for a judicious choice of rotation and translation speeds. It can be linked to an affected zone of average thickness of 15 µm which encompass the presence of IMC and the chaotic mixing caused by plastic deformation in this area. A thickness of less than 15 µm is not sufficient to ensure a good mechanical resistance of the joint. For a thickness higher than 15 µm, IMC layers become more brittle and less adhesive due to high residual stresses which induces numerous cracks after cooling. This leads to a progressive decrease of the ultimate shear stress supported by the bond. Full article
(This article belongs to the Special Issue Friction Stir Welding and Processing in Alloy Manufacturing)
Figures

Figure 1

Open AccessArticle Failure Analysis of PHILOS Plate Construct Used for Pantalar Arthrodesis Paper I—Analysis of the Plate
Metals 2018, 8(3), 180; doi:10.3390/met8030180
Received: 21 December 2017 / Revised: 5 March 2018 / Accepted: 8 March 2018 / Published: 13 March 2018
PDF Full-text (14289 KB) | HTML Full-text | XML Full-text
Abstract
The failure of a proximal humerus internal locking system (PHILOS) used in a pantalar arthrodesis was investigated in this paper. PHILOS constructs are hybrids using locking and non-locking screws. Both the plate and the screws used in the fusion were obtained for analysis.
[...] Read more.
The failure of a proximal humerus internal locking system (PHILOS) used in a pantalar arthrodesis was investigated in this paper. PHILOS constructs are hybrids using locking and non-locking screws. Both the plate and the screws used in the fusion were obtained for analysis. However, only the plate failure analysis is reported in this paper. The implant had failed in several pieces. Optical and scanning electron microscopic analyses were performed to characterize the failure mode(s) and fracture surface. The chemical composition and mechanical properties of the plate were determined and compared to controlling specifications to manufacture the devices. We found that equivalent tensile strength exceeded at the locations of high stress, axial, and angular displacement and matched the specification at the regions of lower stress/displacement. Such a region-wise change in mechanical properties with in vivo utilization has not been reported in the literature. Evidence of inclusions was qualitatively determined for the stainless steel 316L plate failing the specifications. Pitting corrosion, scratches, discoloration and debris were present on the plate. Fracture surface showed (1) multi-site corrosion damage within the screw holes forming a 45° maximum shear force line for crack-linking, and (2) crack propagation perpendicular to the crack forming origin that may have formed due to the presence of inclusions. Fracture features such as beach marks and striations indicating that corrosion may have initiated the crack(s), which grew by fatigue over a period of time. In conclusion, the most likely mechanism of failure for the device was due to corrosion fatigue and lack of bony in-growth on the screws that may have caused loosening of the device causing deformity and pre-mature failure. Full article
(This article belongs to the Special Issue Failure Analysis of Biometals)
Figures

Figure 1

Open AccessArticle A Combined Hybrid 3-D/2-D Model for Flow and Solidification Prediction during Slab Continuous Casting
Metals 2018, 8(3), 182; doi:10.3390/met8030182
Received: 11 December 2017 / Revised: 19 January 2018 / Accepted: 8 March 2018 / Published: 14 March 2018
PDF Full-text (9346 KB) | HTML Full-text | XML Full-text
Abstract
A combined hybrid 3-D/2-D simulation model was developed to investigate the flow and solidification phenomena in turbulent flow and laminar flow regions during slab continuous casting (CC). The 3-D coupling model and 2-D slicing model were applied to the turbulent flow and laminar
[...] Read more.
A combined hybrid 3-D/2-D simulation model was developed to investigate the flow and solidification phenomena in turbulent flow and laminar flow regions during slab continuous casting (CC). The 3-D coupling model and 2-D slicing model were applied to the turbulent flow and laminar flow regions, respectively. In the simulation model, the uneven distribution of cooling water in the width direction of the strand was taken into account according to the nozzle collocation of secondary cooling zones. The results from the 3-D turbulent flow region show that the impact effect of the molten steel jet on the formation of a solidification shell is significant. The impact point is 457 mm below the meniscus, and the plug flow is formed 2442 mm below the meniscus. In the laminar flow region, grid independence tests indicate that the grids with a cell size of 10 × 10 mm2 are sufficient in simulations to attain the precise temperature distribution and solidification profile. The liquid core of the strand is not entirely uniform, and the solidification profile agrees well with the integrated distribution of cooling water in secondary cooling zones. The final solidification points are at a position of 400–500 mm in the width direction and are 17.66 m away from the meniscus. Full article
(This article belongs to the Special Issue Continuous Casting of Steel)
Figures

Figure 1

Open AccessArticle Numerical Modelling of Microstructure Evolution in Friction Stir Welding (FSW)
Metals 2018, 8(3), 183; doi:10.3390/met8030183
Received: 6 February 2018 / Revised: 9 March 2018 / Accepted: 9 March 2018 / Published: 14 March 2018
PDF Full-text (5910 KB) | HTML Full-text | XML Full-text
Abstract
This work studies the metallurgical and microstructural aspects of Friction Stir Welding (FSW) in terms of grain size and microhardness. The modelling is based on the combination of an apropos kinematic framework for the local simulation of FSW processes and a material particle
[...] Read more.
This work studies the metallurgical and microstructural aspects of Friction Stir Welding (FSW) in terms of grain size and microhardness. The modelling is based on the combination of an apropos kinematic framework for the local simulation of FSW processes and a material particle tracing technique for tracking the material flow during the weld. The resulting grain size and microhardness values are validated with experimental observations from an identical processed sample. A Sheppard-Wright constitutive relation is adopted to describe the mechanical behavior of AZ31 Mg alloy considered in this work. The strain rate and temperature histories obtained from the numerical model are stored on the tracers. The relationship among the grain size, microhardness, strain rate, and temperature is obtained using Zener-Hollomon parameter and Hall-Petch relationship. A linear description relates the logarithm of average grain size to the logarithm of Zener-Hollomon parameter. The relationship between microhardness and average grain size stands away from the linear trend. Full article
Figures

Figure 1

Open AccessArticle A Hot Extrusion Process without Sintering by Applying MWCNTs/Al6061 Composites
Metals 2018, 8(3), 184; doi:10.3390/met8030184
Received: 16 January 2018 / Revised: 16 February 2018 / Accepted: 6 March 2018 / Published: 14 March 2018
PDF Full-text (6058 KB) | HTML Full-text | XML Full-text
Abstract
For carbon nanotube (CNT)/Al composites, compaction forming is conducted for densification processing, and then sintering and secondary processes are conducted. This general process has problems such as the complexity of the processing procedures, and high manufacturing costs. This study presents a hot extrusion
[...] Read more.
For carbon nanotube (CNT)/Al composites, compaction forming is conducted for densification processing, and then sintering and secondary processes are conducted. This general process has problems such as the complexity of the processing procedures, and high manufacturing costs. This study presents a hot extrusion process without sintering for fabrication of CNTs/Al6061 composites. Before hot extrusion, preforms are fabricated by the compaction process for the mixture of Al6061 power and CNTs. Several hot extrusion experiments were performed under six types of CNT content; three extrusion ratios and three extrusion temperatures. The formability increased as the extrusion temperature increased for low CNT content. At 620 °C, the forming of all materials except for 10 vol % CNTs/Al6061 was possible at extrusion ratios R = 4, R = 8, and R = 16. As CNT content increases, extrusion pressure almost linearly increases. As the extrusion ratio increases, the extrusion pressure increases. The amount of CNT content increases as Vickers hardness increases. The Vicker’s hardness of 1 vol % CNTs/Al6061 billet is about 100 HV while that of 10 vol % CNTs/Al6061 billet is about 230 HV. There are no significant differences of compression stress according to extrusion ratio as observed in terms of pure Al6061, 1 vol % CNT/Al6061, and 3 vol % CNTs/Al6061. Full article
(This article belongs to the Special Issue Advanced Mechanical Testing of Powder Metallurgy Alloys)
Figures

Figure 1

Open AccessArticle Analysis of Microstructure and Chip Formation When Machining Ti-6Al-4V
Metals 2018, 8(3), 185; doi:10.3390/met8030185
Received: 2 February 2018 / Revised: 13 March 2018 / Accepted: 13 March 2018 / Published: 14 March 2018
Cited by 1 | PDF Full-text (40877 KB) | HTML Full-text | XML Full-text
Abstract
Microstructure and chip formation were evaluated during the step shoulder down-milling of Ti-6Al-4V using a water-miscible vegetable oil-based cutting fluid. Experiments were conducted using the Cut-list fluid supply system previous developed by the authors and a conventional cutting fluid supply system. A thin
[...] Read more.
Microstructure and chip formation were evaluated during the step shoulder down-milling of Ti-6Al-4V using a water-miscible vegetable oil-based cutting fluid. Experiments were conducted using the Cut-list fluid supply system previous developed by the authors and a conventional cutting fluid supply system. A thin plastically deformed layer below the machined surface was observed during the metallurgical investigation of the surfaces produced using both systems. Despite noticeable reductions in cutting fluid consumption achieved by Cut-list, no significant disparity was found in microstructural damage. The microstructure of the machined surfaces was strongly affected by cutting speed and fluid flow rate with a discontinuous serrated chip being the principal type. However, increases in cutting fluid flow rate associated with increased cutting speed significantly changed chip morphology where average distance between chip segments increased with cutting speed. Cut-list produced smaller saw-tooth height and larger segmented width, while the transition from aperiodic to periodic serrated chip formation was governed by cutting speed and feed rate. Chip segmentation frequency and shear angle were also sensitive to cutting speed. Full article
Figures

Figure 1

Open AccessArticle Flow Behavior Characteristics and Processing Map of Fe-6.5wt. %Si Alloys during Hot Compression
Metals 2018, 8(3), 186; doi:10.3390/met8030186
Received: 11 February 2018 / Revised: 8 March 2018 / Accepted: 12 March 2018 / Published: 15 March 2018
PDF Full-text (12122 KB) | HTML Full-text | XML Full-text
Abstract
The flow behavior of Fe-6.5wt. %Si alloys during hot compression was investigated at temperatures 650–950 °C and strain rates 0.01–10 s−1. The results showed that the flow stress depended distinctly on the deformation temperatures and strain rates. The flow stress and
[...] Read more.
The flow behavior of Fe-6.5wt. %Si alloys during hot compression was investigated at temperatures 650–950 °C and strain rates 0.01–10 s−1. The results showed that the flow stress depended distinctly on the deformation temperatures and strain rates. The flow stress and work hardening rate increased with the decrease of temperature and the increase of strain rate. The activation energy under all the deformation conditions was calculated to be 410 kJ/mol. The constitutive equation with hyperbolic sine function and Zener–Hollomon parameter was developed. The peak stress, critical stress, and steady-state stress could be represented as σ = A + Bln(Z/A). Dynamic recrystallization occurred under the deformation conditions where the values of Z were lower than 1020. Processing maps were established to optimize the processing parameters. The power dissipation efficiency decreased in the high temperature and low strain rate region, increased in the high temperature and high strain rate region, and remained unchanged in other regions with the increase of true strain. Furthermore, the unstable area expanded. The true strain of 0.7 was the optimum reduction according to the processing map. Based on the analysis of surface quality, microstructures, and ordered structures, the optimized processing parameters for the Fe-6.5wt. %Si alloys were the temperature and strain rate of higher than 900 °C and 0.01–10 s−1, respectively, or 800–900 °C and lower than 0.4 s−1, respectively. Full article
Figures

Figure 1

Open AccessArticle A Study on the Microstructural Evolution of a Low Alloy Steel by Different Shot Peening Treatments
Metals 2018, 8(3), 187; doi:10.3390/met8030187
Received: 26 February 2018 / Revised: 12 March 2018 / Accepted: 13 March 2018 / Published: 15 March 2018
PDF Full-text (4435 KB) | HTML Full-text | XML Full-text
Abstract
Recent studies have shown that severe shot peening can be categorized as a severe plastic deformation surface treatment that is able to strongly modify the microstructure of the surface layer of materials, by both increasing the dislocation density and introducing a large number
[...] Read more.
Recent studies have shown that severe shot peening can be categorized as a severe plastic deformation surface treatment that is able to strongly modify the microstructure of the surface layer of materials, by both increasing the dislocation density and introducing a large number of defects that define new grain boundaries and form ultrafine structure. In this work, conventional shot peening and severe shot peening treatments were applied to 39NiCrMo3 steel samples. The samples were characterized in terms of microstructure, surface roughness, microhardness, residual stresses, and surface work-hardening as a function of surface coverage. Particular attention was focused on the analysis of the microstructure to assess the evolution of grain size from the surface to the inner material to capture the gradient microstructure. Severe shot peening proved to cause a more remarkable improvement of the general mechanical characteristics compared to conventional shot peening; more significant improvement was associated with the microstructural alteration induced by the treatment. Our datas provide a detailed verification of the relationship between shot peening treatment parameters and the microstructure evolution from the treated surface to the core material. Full article
(This article belongs to the Special Issue Kinetic Surface Treatments)
Figures

Figure 1

Open AccessArticle Effects of Porosity on Mechanical Properties and Corrosion Resistances of PM-Fabricated Porous Ti-10Mo Alloy
Metals 2018, 8(3), 188; doi:10.3390/met8030188
Received: 30 January 2018 / Revised: 3 March 2018 / Accepted: 14 March 2018 / Published: 15 March 2018
Cited by 1 | PDF Full-text (5608 KB) | HTML Full-text | XML Full-text
Abstract
Porous binary Ti-10Mo alloys were prepared using non-spherical titanium, molybdenum powders by the powder metallurgy (PM) space holder technique. Based on the three-dimensional analysis of porosity characteristics, a detailed assessment of the effects of porosity on mechanical properties and corrosion resistances in phosphate-buffered
[...] Read more.
Porous binary Ti-10Mo alloys were prepared using non-spherical titanium, molybdenum powders by the powder metallurgy (PM) space holder technique. Based on the three-dimensional analysis of porosity characteristics, a detailed assessment of the effects of porosity on mechanical properties and corrosion resistances in phosphate-buffered saline (PBS) was carried out. For comparison, PM-fabricated CP-Ti with 50.5% porosity sintered at 1200 °C for 2 h and dense Ti-10Mo alloy sintered at 1450 °C for 2 h (relative density is 97.2% and porosity is 2.8%) were studied simultaneously. The results show that with the space-holder volume contents rising from 63 to 79%, the open porosity and average pore size (d50) increase remarkably, while the pore size distribution (d10d90) tends to be stable at about 100 μm. The average pore sizes (d50) of porous Ti-10Mo alloy can be controlled in the range of 70–380 μm. The PM-fabricated porous Ti-10Mo alloy can achieve a wide range of mechanical properties, with yield compression strength of 248.2–76.9 MPa, and elastic modulus of 6.4–1.7 GPa. In addition, the yield compression strength and the elastic modulus meet the linear regression and exponential formula, respectively. With the porosity of Ti-10Mo alloy increasing from 2.8 to 66.9%, the corrosion rate rises exponentially from 1.6 g/m2·day to 17.1 g/m2·day. In comparison to CP Ti with nearly the same porosity, Ti-10Mo alloy shows significantly higher corrosion resistance. As a result, the relationships between porosity and mechanical properties, corrosion resistances of Ti-10Mo alloys were established, which can be used as a design reference in material selection for orthopedic applications. Full article
(This article belongs to the Special Issue Powder Synthesis and Processing)
Figures

Figure 1

Open AccessArticle Effect of Heating Mode on Sinterability of YSZ+CeO2 Ceramics
Metals 2018, 8(3), 189; doi:10.3390/met8030189
Received: 10 February 2018 / Revised: 3 March 2018 / Accepted: 6 March 2018 / Published: 16 March 2018
PDF Full-text (7799 KB) | HTML Full-text | XML Full-text
Abstract
In the current research work, a comparative study on densification and microstructural evolution of CeO2 particle reinforced 8 mol % yttria stabilized zirconia (YSZ) sintered ceramics has been carried out. The ceramic compacts were fabricated via microwave and conventional sintering methods. The
[...] Read more.
In the current research work, a comparative study on densification and microstructural evolution of CeO2 particle reinforced 8 mol % yttria stabilized zirconia (YSZ) sintered ceramics has been carried out. The ceramic compacts were fabricated via microwave and conventional sintering methods. The sintering conditions that were used for microwave and conventional methods are 1400 °C for 20 min and 1400 °C for 5 h, respectively. The sintered samples were characterized for densification, microstructural behavior, and hardness. Microwave sintering method of sintering resulted in high sintered densities as compared to the conventional counter parts. Microwave sintered samples exhibited finer grains as compared to conventionally sintered specimens. The grain size of the 8YSZ+CeO2 sintered ceramics was found to decrease with CeO2 addition. The X-ray diffraction (XRD) results showed no phase change because of CeO2 addition. The Vickers hardness was found to increase with increasing amount of CeO2. Full article
Figures

Figure 1

Open AccessFeature PaperArticle An Energetic Approach to Predict the Effect of Shot Peening-Based Surface Treatments
Metals 2018, 8(3), 190; doi:10.3390/met8030190
Received: 13 February 2018 / Revised: 12 March 2018 / Accepted: 13 March 2018 / Published: 17 March 2018
PDF Full-text (2267 KB) | HTML Full-text | XML Full-text
Abstract
Almen intensity and surface coverage are well-known to be the defining parameters of shot peening-based surface treatments. These parameters are directly affected by material properties, the extension of the contact zone, the geometry of the impact pair, as well as the impact rate
[...] Read more.
Almen intensity and surface coverage are well-known to be the defining parameters of shot peening-based surface treatments. These parameters are directly affected by material properties, the extension of the contact zone, the geometry of the impact pair, as well as the impact rate and velocity. Such intricate relationships have resulted in often dissimilar predictions of shot peening effects even while using an identical combination of Almen intensity and surface coverage. With the fast pace introduction of new generation impact-based surface treatments, there is a need to find a more widespread parameter that would facilitate the direct comparison of all different treatments and relate the main process parameters to the resultant mechanical characteristics. Herein, we propose to use an energy-based parameter to describe the peening process in a more widespread approach, which collectively incorporates the effects of the Almen intensity and surface coverage, as well as the diameter, material, and velocity of the impact media. A set of finite element analyses was developed to demonstrate the correlation of the peening process effects with this energetic approach. Comparisons with the experimental data served as proof of concept, confirming that the proposed method could provide a quite good estimation of the effect of peening parameters on the treated material. Full article
(This article belongs to the Special Issue Kinetic Surface Treatments)
Figures

Figure 1

Open AccessArticle Mechanical Properties of ARMCO® Iron after Large and Severe Plastic Deformation—Application Potential for Precursors to Ultrafine Grained Microstructures
Metals 2018, 8(3), 191; doi:10.3390/met8030191
Received: 22 December 2017 / Revised: 19 February 2018 / Accepted: 14 March 2018 / Published: 17 March 2018
PDF Full-text (13480 KB) | HTML Full-text | XML Full-text
Abstract
Ultrafine grained (UFG) metals processed by severe plastic deformation (SPD) are well known for their outstanding mechanical properties, yet, current applications are very limited mostly due to the elaborate processing. The present work investigates the microstructures and mechanical properties of precursors to UFG
[...] Read more.
Ultrafine grained (UFG) metals processed by severe plastic deformation (SPD) are well known for their outstanding mechanical properties, yet, current applications are very limited mostly due to the elaborate processing. The present work investigates the microstructures and mechanical properties of precursors to UFG microstructures that evolve at strains below the levels required for UFG microstructures, which implies less processing effort. ARMCO® iron is subjected to a single pass of equal channel angular pressing (ECAP), cold rolling, as well as a combination of both processes and compared to strain–free samples and a UFG reference condition subjected to five ECAP passes. All conditions are characterized regarding their microstructures and mechanical properties using electron backscatter diffraction, tensile tests, and rotating bending fatigue test. The precursor states show intermediate properties in between those of the strain-free and the UFG reference condition. Compared to the processing effort, the difference in properties between precursors and UFG reference is relatively small. Especially a combination of a single ECAP pass followed by cold rolling is a good compromise in terms of processing effort and mechanical properties with an endurance limit being less than 10% lower as compared to the UFG reference condition. Full article
(This article belongs to the Special Issue Synthesis and Properties of Bulk Nanostructured Metallic Materials)
Figures

Figure 1

Open AccessArticle High Speed Finish Turning of Inconel 718 Using PCBN Tools under Dry Conditions
Metals 2018, 8(3), 192; doi:10.3390/met8030192
Received: 23 February 2018 / Revised: 14 March 2018 / Accepted: 15 March 2018 / Published: 17 March 2018
PDF Full-text (3787 KB) | HTML Full-text | XML Full-text
Abstract
Inconel 718 is a superalloy, considered one of the least machinable materials. Tools must withstand a high level of temperatures and pressures in a very localized area, the abrasiveness of the hard carbides contained in the Inconel 718 microstructure and the adhesion tendency
[...] Read more.
Inconel 718 is a superalloy, considered one of the least machinable materials. Tools must withstand a high level of temperatures and pressures in a very localized area, the abrasiveness of the hard carbides contained in the Inconel 718 microstructure and the adhesion tendency during its machining. Mechanical properties along with the low thermal conductivity become an important issue for the tool wear. The finishing operations for Inconel 718 are usually performed after solution heat treatment and age hardening of the material to give the superalloy a higher level of hardness. Carbide tools, cutting fluid (at normal or high pressures) and low cutting speed are the main recommendations for finish turning of Inconel 718. However, dry machining is preferable to the use of cutting fluids, because of its lower environmental impact and cost. Previous research has concluded that the elimination of cutting fluid in these processes is feasible when using hard carbide tools. Recent development of new PCBN (Polycrystalline Cubic Boron Nitride) grades for cutting tools with higher tenacity has allowed the application of these tool grades in the finishing operations of Inconel 718. This work studies the performance of commercial PCBN tools from four different tool manufacturers as well as an additional grade with equivalent performance during finish turning of Inconel 718 under dry conditions. Wear tests were carried out with different cutting conditions, determining the evolution of machining forces, surface roughness and tool wear. It is concluded that it is not industrially viable the high-speed finishing of Inconel 718 in a dry environment. Full article
(This article belongs to the Special Issue Machining and Finishing of Nickel and Titanium Alloys)
Figures

Figure 1

Open AccessArticle Evaluation of Workability on the Microstructure and Mechanical Property of Modified 9Cr-2W Steel for Fuel Cladding by Cold Drawing Process and Intermediate Heat Treatment Condition
Metals 2018, 8(3), 193; doi:10.3390/met8030193
Received: 5 January 2018 / Revised: 13 March 2018 / Accepted: 14 March 2018 / Published: 18 March 2018
PDF Full-text (3656 KB) | HTML Full-text | XML Full-text
Abstract
In this study, we evaluated the cold drawing workability of two kinds of modified 9Cr-2W steel containing different contents of boron and nitrogen depending on the temperature and time of normalizing and tempering treatments. Using ring compression tests at room temperature, the effect
[...] Read more.
In this study, we evaluated the cold drawing workability of two kinds of modified 9Cr-2W steel containing different contents of boron and nitrogen depending on the temperature and time of normalizing and tempering treatments. Using ring compression tests at room temperature, the effect of intermediate heat treatment condition on workability was investigated. It was found that the prior austenite grain size can be changed by the austenite transformation and that the grain size increases with increasing temperature during normalizing heat treatment. Alloy B and Alloy N showed different patterns after normalizing heat treatment. Alloy N had higher stress than Alloy B, and the reduction in alloy N increased while the reduction in alloy B decreased. Alloy B showed a larger number of initially formed cracks and a larger average crack length than Alloy N. Crack length and number increased proportionally in Alloy B as the stress increased. Alloy B had lower crack resistance than Alloy N due to boron segregation. Full article
Figures

Figure 1

Open AccessArticle Effect of Trace Be and Sc Additions on the Mechanical Properties of A357 Alloys
Metals 2018, 8(3), 194; doi:10.3390/met8030194
Received: 8 February 2018 / Revised: 13 March 2018 / Accepted: 17 March 2018 / Published: 19 March 2018
PDF Full-text (7133 KB) | HTML Full-text | XML Full-text
Abstract
The effect of the addition of Be and Sc on the microstructure and mechanical properties of A357 alloy were systematically investigated. The results show that the addition of small amounts of Be and Sc could change the acicular structure of iron-bearing intermetallic compounds
[...] Read more.
The effect of the addition of Be and Sc on the microstructure and mechanical properties of A357 alloy were systematically investigated. The results show that the addition of small amounts of Be and Sc could change the acicular structure of iron-bearing intermetallic compounds to harmless compact Al-Fe-Si and Sc-Fe iron-bearing intermetallic compounds. Compact iron-bearing intermetallic compounds could improve fluidity, causing a reduction in interdendritic shrinkage during solidification. The addition of 0.05 wt % Be enhanced the quality index of the A357 alloy by 11% and increased the notch-yield ratio of fracture toughness by 4.5%. In contrast, the addition of 0.05 wt % Sc increased the quality index and the notch to yield ratio of fracture toughness up to 17% and 9%, respectively. Therefore, the microstructure and mechanical properties of the A357 alloy could be improved by substituting Be with Sc. Full article
Figures

Figure 1

Open AccessArticle Stress Corrosion Cracking Behaviour of Dissimilar Welding of AISI 310S Austenitic Stainless Steel to 2304 Duplex Stainless Steel
Metals 2018, 8(3), 195; doi:10.3390/met8030195
Received: 7 December 2017 / Revised: 1 February 2018 / Accepted: 5 February 2018 / Published: 20 March 2018
PDF Full-text (8726 KB) | HTML Full-text | XML Full-text
Abstract
The influence of the weld metal chemistry on the stress corrosion cracking (SCC) susceptibility of dissimilar weldments between 310S austenitic stainless steel and 2304 duplex steels was investigated by constant load tests and microstructural examination. Two filler metals (E309L and E2209) were used
[...] Read more.
The influence of the weld metal chemistry on the stress corrosion cracking (SCC) susceptibility of dissimilar weldments between 310S austenitic stainless steel and 2304 duplex steels was investigated by constant load tests and microstructural examination. Two filler metals (E309L and E2209) were used to produce fusion zones of different chemical compositions. The SCC results showed that the heat affected zone (HAZ) on the 2304 base metal side of the weldments was the most susceptible region to SCC for both filler metals tested. The SCC results also showed that the weldments with 2209 duplex steel filler metal presented the best SCC resistance when compared to the weldments with E309L filler metal. The lower SCC resistance of the dissimilar joint with 309L austenitic steel filler metal may be attributed to (1) the presence of brittle chi/sigma phase in the HAZ on the 2304 base metal, which produced SC cracks in this region and (2) the presence of a semi-continuous delta-ferrite network in the fusion zone which favored the nucleation and propagation of SC cracks from the fusion zone to HAZ of the 2304 stainless steel. Thus, the SC cracks from the fusion zone associated with the SC cracks of 2304 HAZ decreased considerably the time-of-fracture on this region, where the fracture occurred. Although the dissimilar weldment with E2209 filler metal also presented SC cracks in the HAZ on the 2304 side, it did not present the delta ferrite network in the fusion zone due to its chemical composition. Fractography analyses showed that the mixed fracture mode was predominant for both filler metals used. Full article
Figures

Figure 1

Open AccessArticle Martensitic Transformation and Plastic Deformation of TiCuNiZr-Based Bulk Metallic Glass Composites
Metals 2018, 8(3), 196; doi:10.3390/met8030196
Received: 7 February 2018 / Revised: 15 March 2018 / Accepted: 16 March 2018 / Published: 20 March 2018
PDF Full-text (3100 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
In this study, the microstructural evolution and mechanical properties of TiCuNiZr-based bulk metallic glass (BMGs) composites were systematically investigated in order to optimize both the strength and the ductility of BMGs. By tailoring the glass-forming compositions, TiCuNiZr-based BMG composites with different volume fractions
[...] Read more.
In this study, the microstructural evolution and mechanical properties of TiCuNiZr-based bulk metallic glass (BMGs) composites were systematically investigated in order to optimize both the strength and the ductility of BMGs. By tailoring the glass-forming compositions, TiCuNiZr-based BMG composites with different volume fractions of B2 (Ti,Zr)(Cu,Ni) crystals precipitating in the glassy matrix exhibit not only macroscopic ductility but also high strength as well as work-hardening, which is due to the formation of multiple shear bands and martensitic transformation during deformation. Optimized mechanical properties can be achieved when the crystalline volume fraction is at least higher than 44 vol. %, which is attributed to the sizeable difference between Young’s moduli of the B2 (Ti,Zr)(Cu,Ni) crystals and the glassy matrix, and the precipitation of Ti2Cu intermetallic compounds at the B2 crystal boundaries. Our study provides a complementary understanding of how to tailor mechanical properties of TiCu-based BMG composites. Full article
(This article belongs to the Special Issue Metallic Glasses: Pathways to Viable Applications)
Figures

Figure 1

Open AccessArticle Online Surface Defect Identification of Cold Rolled Strips Based on Local Binary Pattern and Extreme Learning Machine
Metals 2018, 8(3), 197; doi:10.3390/met8030197
Received: 12 February 2018 / Revised: 14 March 2018 / Accepted: 17 March 2018 / Published: 20 March 2018
PDF Full-text (3657 KB) | HTML Full-text | XML Full-text
Abstract
In the production of cold-rolled strip, the strip surface may suffer from various defects which need to be detected and identified using an online inspection system. The system is equipped with high-speed and high-resolution cameras to acquire images from the moving strip surface.
[...] Read more.
In the production of cold-rolled strip, the strip surface may suffer from various defects which need to be detected and identified using an online inspection system. The system is equipped with high-speed and high-resolution cameras to acquire images from the moving strip surface. Features are then extracted from the images and are used as inputs of a pre-trained classifier to identify the type of defect. New types of defect often appear in production. At this point the pre-trained classifier needs to be quickly retrained and deployed in seconds to meet the requirement of the online identification of all defects in the environment of a continuous production line. Therefore, the method for extracting the image features and the training for the classification model should be automated and fast enough, normally within seconds. This paper presents our findings in investigating the computational and classification performance of various feature extraction methods and classification models for the strip surface defect identification. The methods include Scale Invariant Feature Transform (SIFT), Speeded Up Robust Features (SURF) and Local Binary Patterns (LBP). The classifiers we have assessed include Back Propagation (BP) neural network, Support Vector Machine (SVM) and Extreme Learning Machine (ELM). By comparing various combinations of different feature extraction and classification methods, our experiments show that the hybrid method of LBP for feature extraction and ELM for defect classification results in less training and identification time with higher classification accuracy, which satisfied online real-time identification. Full article
Figures

Figure 1

Review

Jump to: Research

Open AccessReview Distinct Fracture Patterns in Construction Steels for Reinforced Concrete under Quasistatic Loading— A Review
Metals 2018, 8(3), 171; doi:10.3390/met8030171
Received: 6 February 2018 / Revised: 28 February 2018 / Accepted: 4 March 2018 / Published: 9 March 2018
PDF Full-text (13859 KB) | HTML Full-text | XML Full-text
Abstract
Steel is one of the most widely used materials in construction. Nucleation growth and coalescence theory is usually employed to explain the fracture process in ductile materials, such as many metals. The typical cup–cone fracture pattern has been extensively studied in the past,
[...] Read more.
Steel is one of the most widely used materials in construction. Nucleation growth and coalescence theory is usually employed to explain the fracture process in ductile materials, such as many metals. The typical cup–cone fracture pattern has been extensively studied in the past, giving rise to numerical models able to reproduce this pattern. Nevertheless, some steels, such as the eutectoid steel used for manufacturing prestressing wires, does not show this specific shape but a flat surface with a dark region in the centre of the fracture area. Recent studies have deepened the knowledge on these distinct fracture patterns, shedding light on some aspects that help to understand how damage begins and propagates in each case. The numerical modelling of both fracture patterns have also been discussed and reproduced with different approaches. This work reviews the main recent advances in the knowledge on this subject, particularly focusing on the experimental work carried out by the authors. Full article
(This article belongs to the Special Issue Mechanical Behavior of High-Strength Low-Alloy Steels)
Figures

Figure 1

Open AccessReview An Overview of Key Challenges in the Fabrication of Metal Matrix Nanocomposites Reinforced by Graphene Nanoplatelets
Metals 2018, 8(3), 172; doi:10.3390/met8030172
Received: 25 January 2018 / Revised: 28 February 2018 / Accepted: 9 March 2018 / Published: 10 March 2018
PDF Full-text (6082 KB) | HTML Full-text | XML Full-text
Abstract
This article provides an overview of research efforts with an emphasis on the fabrication of metal matrix nanocomposites (MMNCs) reinforced by graphene nanoplatelets (GNPs). Particular attention is devoted to finding the challenges in the production of MMNCs through the powder metallurgy techniques. The
[...] Read more.
This article provides an overview of research efforts with an emphasis on the fabrication of metal matrix nanocomposites (MMNCs) reinforced by graphene nanoplatelets (GNPs). Particular attention is devoted to finding the challenges in the production of MMNCs through the powder metallurgy techniques. The main technical challenges can be listed as: (I) reinforcement selection; (II) dispersion of reinforcement within the matrix; (III) reactivity between the reinforcement and matrix; (IV) interfacial bonding; (V) preferred orientation of reinforcement. It is found that some of these difficulties can be attributed to the nature of the materials involved, while the others are related to the preparation routes. It is reported that the challenges related to the process can often be addressed by changing the production process or by using post-processing techniques. More challenging issues instead are related to the composition of the matrix and reinforcement, their reactivity and the dispersion of reinforcement. These topics still bring significant challenges to the materials scientists, and it would be worth mentioning that the fabrication of MMNCs with a uniform dispersion of reinforcement, strong interfacial bonding, without detrimental reactions and improved isotropic properties is still a puzzling issue. Full article
(This article belongs to the Special Issue Processing of Metal Matrix Composites)
Figures

Figure 1

Open AccessReview Microstructure and Properties of Semi-Solid Aluminum Alloys: A Literature Review
Metals 2018, 8(3), 181; doi:10.3390/met8030181
Received: 4 February 2018 / Revised: 6 March 2018 / Accepted: 6 March 2018 / Published: 13 March 2018
PDF Full-text (7734 KB) | HTML Full-text | XML Full-text
Abstract
Semi-solid processing of aluminum alloys is a well-known manufacturing technique able to combine high production rates with parts quality, resulting in high performance and reasonable component costs. The advantages offered by semi-solid processing are due to the shear thinning behavior of the thixotropic
[...] Read more.
Semi-solid processing of aluminum alloys is a well-known manufacturing technique able to combine high production rates with parts quality, resulting in high performance and reasonable component costs. The advantages offered by semi-solid processing are due to the shear thinning behavior of the thixotropic slurries during the mold filling. This is related to the microstructure of these slurries consisting of solid, nondendritic, near-globular primary particles surrounded by a liquid matrix. This paper presents a review on the formation of this nondendritic microstructure, reports on the different proposed mechanisms that might be responsible, and illustrates the relationship between microstructure and properties, in particular, tensility, fatigue, wear, and corrosion resistance. Full article
(This article belongs to the Special Issue Semi-solid Processing of Alloys and Composites)
Figures

Figure 1

Back to Top