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Metals, Volume 7, Issue 4 (April 2017)

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Cover Story Ultrafine grained cams may be obtained from previously ECAP (Equal Channel Angular [...] Read more.
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Editorial

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Open AccessEditorial Aluminium Production Process: Challenges and Opportunities
Metals 2017, 7(4), 133; doi:10.3390/met7040133
Received: 29 March 2017 / Revised: 29 March 2017 / Accepted: 6 April 2017 / Published: 11 April 2017
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Abstract Aluminium, with more than 50 Mt annual production in 2016, is an essential material in modern engineering designs of lightweight structures.[...] Full article

Research

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Open AccessArticle An Investigation on the Softening Mechanism of 5754 Aluminum Alloy during Multistage Hot Deformation
Metals 2017, 7(4), 107; doi:10.3390/met7040107
Received: 12 January 2017 / Revised: 1 March 2017 / Accepted: 13 March 2017 / Published: 23 March 2017
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Abstract
Isothermal interrupted hot compression tests of 5754 aluminum were conducted on a Gleeble-3500 thermo-mechanical simulator at temperatures of 350 °C and 450 °C, and strain rates of 0.1 s−1 and 1 s−1. To investigate the metadynamic recrystallization behavior, a range
[...] Read more.
Isothermal interrupted hot compression tests of 5754 aluminum were conducted on a Gleeble-3500 thermo-mechanical simulator at temperatures of 350 °C and 450 °C, and strain rates of 0.1 s−1 and 1 s−1. To investigate the metadynamic recrystallization behavior, a range of inter-pass delay times (5–60 s) was employed. These tests simulated flat rolling to investigate how softening behaviors respond to controlled parameters, such as deformation temperature, strain rate, and delay times. These data allowed the parameters for the hot rolling process to be optimized. The dynamic softening at each pass and the effect of metadynamic recrystallization on flow properties and microstructural evolution were analyzed in detail. An offset yield strength of 0.2% was employed to calculate the softening fraction undergoing metadynamic recrystallization. A kinetic model was developed to describe the metadynamic recrystallization behaviors of the hot-deformed 5754 aluminum alloy. Furthermore, the time constant for 50% recrystallization was expressed as functions related to the temperature and the strain rate. The experimental and calculated results were found to be in close agreement, which verified the developed model. Full article
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Open AccessArticle Measuring Plasticity with Orientation Contrast Microscopy in Aluminium 6061-T4
Metals 2017, 7(4), 108; doi:10.3390/met7040108
Received: 22 February 2017 / Revised: 12 March 2017 / Accepted: 17 March 2017 / Published: 23 March 2017
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Abstract
Orientation contrast microscopy (i.e., electron backscattered diffraction, EBSD) was employed to monitor the plastic strain in loaded tensile samples of aluminium alloy Al6061 in T4 condition. The kernel average misorientation (KAM) is known to be an appropriate parameter in orientation contrast microscopy which
[...] Read more.
Orientation contrast microscopy (i.e., electron backscattered diffraction, EBSD) was employed to monitor the plastic strain in loaded tensile samples of aluminium alloy Al6061 in T4 condition. The kernel average misorientation (KAM) is known to be an appropriate parameter in orientation contrast microscopy which has the potential to characterise the plastic strain by monitoring the local misorientations. This technique was applied here to gauge the extent of the plastic zone around a fatigue crack. To establish the magnitude of strain (which can be identified by the KAM parameter), a series of tensile samples were strained in the range of 1% to 25%. KAM maps were compared, and the average misorientations were related to the tensile strain values. The KAM distribution functions for all the strained samples were derived from a large scanned area. In addition, Vickers microhardness tests were conducted for these series of samples. This allowed the comparison of the mesoscopic plastic strain measured by Vickers microhardness with the micro plastic strain locally obtained by KAM. Noise was observed in the average KAM values up to a plastic strain of 1.5%. For the plastic strain exceeding 1.5%, noise no longer dominates the KAM map, and a positive—though not linear—correspondence between plastic strain and KAM was observed. The observed plastic zone at the tip of the fatigue crack by micro-Vickers hardness measurements was about an order of magnitude higher than the plastic zone observed on the KAM maps. In view of the calibration of KAM values on the tensile samples, it could be concluded that in the larger area of the plastic zone, the strain did not exceed the critical value of 1.5%. Full article
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Open AccessArticle Corrosion Behavior of API X100 Steel Material in a Hydrogen Sulfide Environment
Metals 2017, 7(4), 109; doi:10.3390/met7040109
Received: 8 February 2017 / Revised: 7 March 2017 / Accepted: 14 March 2017 / Published: 25 March 2017
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Abstract
Recently, the API X100 steel has emerged as an important pipeline material for transportation of crude oil and natural gas. At the same time, the presence of significant amounts of hydrogen sulfide (H2S) in natural gas and crude oil cause pipeline
[...] Read more.
Recently, the API X100 steel has emerged as an important pipeline material for transportation of crude oil and natural gas. At the same time, the presence of significant amounts of hydrogen sulfide (H2S) in natural gas and crude oil cause pipeline materials to corrode, which affects their integrity. In this study, the effect of H2S concentration on the corrosion behavior of API X100 in 3.5% NaCl solution is presented. The H2S gas was bubbled into saline solutions for different durations, and the corrosion tests were then performed using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), atomic force microscopy (AFM), and scanning electron microscopy (SEM) techniques were used to characterize the corroded surface. The results indicate that the corrosion rate of API X100 steel decreases with increasing H2S bubbling time due to the increase in H2S concentration in 3.5% NaCl solutions. It is noticed that an accumulation of a critical amount of hydrogen in the metal can result in hydrogen-induced crack initiation and propagation. It was further observed that, when the stress limit of a crystalline layer is exceeded, micro-cracking of the formed protective sulfide layer (mackinawite) occurs on the API X100 steel surface, which may affect the reliability of the pipeline system. Full article
(This article belongs to the Special Issue Alloy Steels)
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Open AccessArticle Applications and Thermodynamic Analysis of Equilibrium Solution for Secondary Phases in Ti–N–C Gear Steel System with Nano-Particles
Metals 2017, 7(4), 110; doi:10.3390/met7040110
Received: 16 February 2017 / Revised: 16 March 2017 / Accepted: 17 March 2017 / Published: 24 March 2017
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Abstract
Thermodynamic analysis and computations of the equilibrium solution for the multivariable secondary phase in steels have been conducted, based on the chemical equilibrium. Solid solution precipitation in the Ti–N–C microalloy steel for the secondary phase was analyzed, and its engineering application in the
[...] Read more.
Thermodynamic analysis and computations of the equilibrium solution for the multivariable secondary phase in steels have been conducted, based on the chemical equilibrium. Solid solution precipitation in the Ti–N–C microalloy steel for the secondary phase was analyzed, and its engineering application in the development of carburizing gear steels was investigated. The complete dissolution temperature increases with more C, N, or Ti in gear steels, and the effects of Ti and N are more significant than C. At a given temperature, the amount of [Ti] increases naturally with more Ti element content, while it decreases with more C or N elements content. It declines rapidly in the complete dissolution temperature range in steels until 1100 °C. The effective activity coefficient k1 increases with the temperature decreases, and increases with the higher content of Ti or C, while it decreases with the higher N content under the same temperature. Thermodynamic analysis shows that nitrogen has been precipitated largely as TiN micron-particles above 1400 °C in gear steels. Then, titanium precipitated mainly as TiC nano-particles, thus this secondary phase can hinder grain coarsening during heat treatment. Full article
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Open AccessArticle Deformation Behavior of Al0.25CoCrFeNi High-Entropy Alloy after Recrystallization
Metals 2017, 7(4), 111; doi:10.3390/met7040111
Received: 27 December 2016 / Revised: 12 March 2017 / Accepted: 21 March 2017 / Published: 24 March 2017
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Abstract
Cold rolling with subsequent annealing can be used to produce the recrystallized structure in high entropy alloys (HEAs). The Al0.25CoCrFeNi HEAs rolled to different final thickness (230, 400, 540, 800, 1000, 1500 μm) are prepared to investigate their microstructure evolutions and
[...] Read more.
Cold rolling with subsequent annealing can be used to produce the recrystallized structure in high entropy alloys (HEAs). The Al0.25CoCrFeNi HEAs rolled to different final thickness (230, 400, 540, 800, 1000, 1500 μm) are prepared to investigate their microstructure evolutions and mechanical behaviors after annealing. Only the single face-centered cubic phase was obtained after cold rolling and recrystallization annealing at 1100 °C for 10 h. The average recrystallized grain size in this alloy after annealing ranges from 92 μm to 136 μm. The annealed thin sheets show obviously size effects on the flow stress and formability. The yield strength and tensile strength decrease as t/d (thickness/average grain diameter) ratio decreases until the t/d approaches 2.23. In addition, the stretchability (formability) decreases with the decrease of the t/d ratio especially when the t/d ratio is lower than about 6. According to the present results, yield strength can be expressed as a function of the t/d ratio. Full article
(This article belongs to the Special Issue High-Entropy Alloys (HEAs))
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Open AccessArticle The Effect of Anchor Volume on the Mechanical Strengths of Orthodontic Micro-Implants
Metals 2017, 7(4), 112; doi:10.3390/met7040112
Received: 20 January 2017 / Revised: 10 March 2017 / Accepted: 23 March 2017 / Published: 25 March 2017
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Abstract
Anchor volume (AV) might be an important factor affecting mechanical strengths of micro-implant. To investigate the correlation between AV and three mechanical strengths (IT: insertion torque; RF: resonance frequency; HPS: horizontal pullout strength), 55 micro-implants (diameter 1.5 mm: Type A, B, C; diameter
[...] Read more.
Anchor volume (AV) might be an important factor affecting mechanical strengths of micro-implant. To investigate the correlation between AV and three mechanical strengths (IT: insertion torque; RF: resonance frequency; HPS: horizontal pullout strength), 55 micro-implants (diameter 1.5 mm: Type A, B, C; diameter 1.3 mm: Type D and E) were driven into the artificial bones at a 7-mm depth. The RF, IT, HPS and AV were measured. One-way analysis of variance (ANOVA) with Tukey Honestly Significant Difference (HSD) post comparison and Pearson’s correlation were used to detect significant differences. Null hypothesis states that there was no statistically significant correlation between AV and these three forces (IT, RF, and HPS). Type A and Type D had the lowest IT (4.2 Ncm). Type C had the highest RF (9.9 KHz) in the stability test, and Type B had the greatest HPS (190.9 Ncm) in the resistance test. There was significant correlation between the IT and HPS. AV was significantly correlated with RF, IT, and HPS. The null hypothesis was rejected. In this study, each of these brands had its distinct advantages in the RF, IT, and HPS. Moreover, inner diameter/outer diameter ratio and AV affect the magnitude of HPS. Full article
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Open AccessArticle Case Studies on Local Reinforcement of Sheet Metal Components by Laser Additive Manufacturing
Metals 2017, 7(4), 113; doi:10.3390/met7040113
Received: 31 December 2016 / Revised: 15 March 2017 / Accepted: 20 March 2017 / Published: 25 March 2017
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Abstract
This paper details two case studies that make use of laser metal deposition for local reinforcement of sheet metal components. Two benchmark scenarios are investigated, both using aluminum alloys: (i) using laser cladding to increase the stiffness of a pre-formed component, and (ii)
[...] Read more.
This paper details two case studies that make use of laser metal deposition for local reinforcement of sheet metal components. Two benchmark scenarios are investigated, both using aluminum alloys: (i) using laser cladding to increase the stiffness of a pre-formed component, and (ii) applying a local cladding on sheet metal for increasing the thickness prior to a hole-flanging operation. The results show that both routes are viable. Applying claddings onto sheet metal before a metal forming operation must ensure suitable formability, which may be limited by the layer material and undesired changes in the microstructure of the sheet. The limited formability has to be taken into account in the design of the forming operation. Cladding onto already formed components has to cope with inevitable distortion of the component. Nevertheless, introducing additive manufacturing into the field of sheet metal forming opens the possibility to produce new products such as tailored laser-cladded blanks, combinations of sheet and bulk components and to develop new methods such as stiffness management in lightweight design. Full article
(This article belongs to the Special Issue 3D Printing of Metals)
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Open AccessArticle Modeling the Constitutive Relationship of Al–0.62Mg–0.73Si Alloy Based on Artificial Neural Network
Metals 2017, 7(4), 114; doi:10.3390/met7040114
Received: 18 February 2017 / Revised: 16 March 2017 / Accepted: 23 March 2017 / Published: 26 March 2017
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Abstract
In this work, the hot deformation behavior of 6A02 aluminum alloy was investigated by isothermal compression tests conducted in the temperature range of 683–783 K and strain-rate range of 0.001–1 s−1. According to the obtained true stress–true strain curves, the constitutive
[...] Read more.
In this work, the hot deformation behavior of 6A02 aluminum alloy was investigated by isothermal compression tests conducted in the temperature range of 683–783 K and strain-rate range of 0.001–1 s−1. According to the obtained true stress–true strain curves, the constitutive relationship of the alloy was revealed by establishing the Arrhenius-type constitutive model and back-propagation (BP) neural network model. It is found that the flow characteristic of 6A02 aluminum alloy is closely related to deformation temperature and strain rate, and the true stress decreases with increasing temperatures and decreasing strain rates. The hot deformation activation energy is calculated to be 168.916 kJ mol−1. The BP neural network model with one hidden layer and 20 neurons in the hidden layer is developed. The accuracy in prediction of the Arrhenius-type constitutive model and BP neural network model is eveluated by using statistics analysis method. It is demonstrated that the BP neural network model has better performance in predicting the flow stress. Full article
(This article belongs to the Special Issue Advances in Plastic Forming of Metals)
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Open AccessArticle Effect of Welding Heat Input on the Microstructure and Toughness in Simulated CGHAZ of 800 MPa-Grade Steel for Hydropower Penstocks
Metals 2017, 7(4), 115; doi:10.3390/met7040115
Received: 22 January 2017 / Revised: 23 March 2017 / Accepted: 23 March 2017 / Published: 27 March 2017
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Abstract
To determine the appropriate welding heat input for simulated coarse grained heat affected zone (CGHAZ) of 800 MPa-grade steel used in hydropower penstocks, the microstructural evolution, hardness, and 50% fraction appearance transition temperature (50% FATT) were investigated. The results indicated that when the
[...] Read more.
To determine the appropriate welding heat input for simulated coarse grained heat affected zone (CGHAZ) of 800 MPa-grade steel used in hydropower penstocks, the microstructural evolution, hardness, and 50% fraction appearance transition temperature (50% FATT) were investigated. The results indicated that when the cooling rate (heat input) is reduced (increased), the impact toughness at −20 °C and hardness of the simulated CGHAZ decreased. When the heat input increased from 18 to 81 kJ/cm, the 50% FATT increased from −80 °C to −11 °C. At 18 kJ/cm, the microstructures consisted of lath bainite and granular bainite, but lath bainite decreased with increasing heat input. The increase in the 50% FATT was attributed mainly to an increase in the austenite grain size and effective grain size, and a decrease in lath bainite and the fraction of HAGBs (misorientation: ≥15°). Full article
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Open AccessArticle Design and Mechanical Properties Analysis of AA5083 Ultrafine Grained Cams
Metals 2017, 7(4), 116; doi:10.3390/met7040116
Received: 14 February 2017 / Revised: 20 March 2017 / Accepted: 22 March 2017 / Published: 28 March 2017
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Abstract
This present research work deals with the development of ultrafine grained cams obtained from previously ECAP (Equal Channel Angular Pressing)-processed material and manufactured by isothermal forging. The design and the manufacturing of the dies required for the isothermal forging of the cams are
[...] Read more.
This present research work deals with the development of ultrafine grained cams obtained from previously ECAP (Equal Channel Angular Pressing)-processed material and manufactured by isothermal forging. The design and the manufacturing of the dies required for the isothermal forging of the cams are shown. Optimization techniques based on the combination of design of experiments, finite element and finite volume simulations are employed to develop the dies. A comparison is made between the mechanical properties obtained with the cams manufactured from material with no previous deformation and with those from previously SPD (Severe Plastic Deformation)-processed material. In addition, a comparative study between the experimental results and those obtained from the simulations is carried out. It has been demonstrated that it is possible to obtain ultrafine grained cams with an increase of 10.3% in the microhardness mean value as compared to that obtained from material with no previous deformation. Full article
(This article belongs to the Special Issue Advances in Plastic Forming of Metals)
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Open AccessArticle Characterization of In-Situ Cu–TiH2–C and Cu–Ti–C Nanocomposites Produced by Mechanical Milling and Spark Plasma Sintering
Metals 2017, 7(4), 117; doi:10.3390/met7040117
Received: 5 February 2017 / Revised: 9 March 2017 / Accepted: 27 March 2017 / Published: 29 March 2017
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Abstract
This study focuses on the fabrication and microstructural investigation of Cu–TiH2–C and Cu–Ti–C nanocomposites with different volume fractions (10% and 20%) of TiC. Two mixtures of powders were ball milled for 10 h, consequently consolidated by spark plasma sintering (SPS) at 900 and
[...] Read more.
This study focuses on the fabrication and microstructural investigation of Cu–TiH2–C and Cu–Ti–C nanocomposites with different volume fractions (10% and 20%) of TiC. Two mixtures of powders were ball milled for 10 h, consequently consolidated by spark plasma sintering (SPS) at 900 and 1000 °C producing bulk materials with relative densities of 95–97%. The evolution process of TiC formation during sintering process was studied by using X-ray diffraction (XRD), scanning electron microscopy (SEM), and high resolution transmission electron microscopy (HRTEM). XRD patterns of composites present only Cu and TiC phases, no residual Ti phase can be detected. TEM images of composites with (10 vol % TiC) sintered at 900 °C show TiC nanoparticles about 10–30 nm precipitated in copper matrix, most of Ti and C dissolved in the composite matrix. At the higher sintering temperature of 1000 °C, more TiC precipitates from Cu–TiH2–C than those of Cu–Ti–C composite, particle size ranges from 10 to 20 nm. The hardness of both nanocomposites also increased with increasing sintering temperature. The highest hardness values of Cu–TiH2–C and Cu–Ti–C nanocomposites sintered at 1000 °C are 314 and 306 HV, respectively. Full article
(This article belongs to the Special Issue Metal Matrix Composites)
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Open AccessArticle Investigating the Wear Behavior of Fe-Based Amorphous Coatings under Nanoscratch Tests
Metals 2017, 7(4), 118; doi:10.3390/met7040118
Received: 23 January 2017 / Revised: 23 March 2017 / Accepted: 24 March 2017 / Published: 29 March 2017
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Abstract
The wear behavior of two coatings (Fe49.7Cr18Mn1.9Mo7.4W1.6B15.2C3.8Si2.4 and Fe40Cr23Mo14C15B6Y2) sprayed by high-velocity air fuel technology was
[...] Read more.
The wear behavior of two coatings (Fe49.7Cr18Mn1.9Mo7.4W1.6B15.2C3.8Si2.4 and Fe40Cr23Mo14C15B6Y2) sprayed by high-velocity air fuel technology was investigated through nanoscratch tests under ramping loads. Compared with the substrate, the Fe-based amorphous coatings exhibit lower penetration depth, higher elastic recovery, and lower wear volume, indicating the excellent wear resistance of the coatings. This behavior is related to the high hardness and high hardness/elastic modulus ratio (H/E) of the Fe-based amorphous coatings. From the scanning electron microscopy images of the scratch grooves, it is found out that ploughing governs the wear behavior of the coatings and substrate. In addition, spalling wear easily occurs in the pore regions of the coatings. Full article
(This article belongs to the Special Issue High-Entropy Alloys (HEAs))
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Open AccessArticle Effects of ECAP and Annealing Treatment on the Microstructure and Mechanical Properties of Mg-1Y (wt. %) Binary Alloy
Metals 2017, 7(4), 119; doi:10.3390/met7040119
Received: 30 December 2016 / Revised: 24 March 2017 / Accepted: 27 March 2017 / Published: 30 March 2017
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Abstract
Microstructure and mechanical properties development of extruded Mg-1Y (wt. %) binary alloy during equal channel angular pressing (ECAP) with route Bc at 400 °C, and subsequent annealing treatment between 300–400 °C at different holding time of 5–120 min were investigated using an
[...] Read more.
Microstructure and mechanical properties development of extruded Mg-1Y (wt. %) binary alloy during equal channel angular pressing (ECAP) with route Bc at 400 °C, and subsequent annealing treatment between 300–400 °C at different holding time of 5–120 min were investigated using an optical and scanning electron microscope (SEM), electron back scattered diffraction (EBSD), tensile test, and hardness test. The grain size of as-extruded material (~10.9 μm) was refined significantly by 1-pass ECAP (~5.8 μm), and resulted in a remarkably enhanced elongation to failure (EL) (~+62%) with a slightly decreased ultimate tensile strength (UTS) (~−3%) comparing to the as-extruded condition (EL = 11.3%, UTS = 200 MPa). The EL was further increased to 27.3% (~+142%) after four passes of ECAP comparing to the as-extruded condition, which was mainly caused by the much more homogenized microstructure. The split basal poles with about 60° rotations to the extruded direction (ED), the relatively coarsened grain size by static recrystallization (SRX) and post-dynamic recrystallization (PDRX) after four passes of ECAP might be responsible for the decreased strength with increasing ECAP pass. During the annealing treatment, recovery dominantly occurred at 300 °C, SRX and grain growth emerged at 350 °C and 400 °C, respectively. Meanwhile, the grain grew and hardness decreased rapidly even within 5 min for 1-pass ECAPed material at 400 °C, indicating a larger grain boundary mobility of ECAPed materials induced by higher deformation energy than the as-extruded ones. Full article
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Open AccessArticle Rheological Characterization of Powder Mixture Including a Space Holder and Its Application to Metal Injection Molding
Metals 2017, 7(4), 120; doi:10.3390/met7040120
Received: 23 February 2017 / Revised: 28 March 2017 / Accepted: 28 March 2017 / Published: 30 March 2017
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Abstract
Metal injection molding (MIM) with the space holder technique is becoming one of the important fabrication methods for a net-shape production of micro-sized, porous, complex-shaped metal parts. For a successful injection molding step, rheological behavior of MIM feedstock is essential, which includes peculiar
[...] Read more.
Metal injection molding (MIM) with the space holder technique is becoming one of the important fabrication methods for a net-shape production of micro-sized, porous, complex-shaped metal parts. For a successful injection molding step, rheological behavior of MIM feedstock is essential, which includes peculiar characteristics, such as a wall slip phenomenon. SUS 316L stainless steel powder, binder systems (paraffin wax, polypropylene, polyethylene, stearic acid) and three different sizes of spherically-shaped polymethyl methacrylate (PMMA) as a space-holder were used for this study. The porosity was controlled by varying the volume fraction of the space holder and a total of six different feedstocks were prepared. Rheological characteristics of the feedstock was investigated, especially on viscosities, including wall slip quantification by using a capillary rheometer. By thermogravimetric analysis, the debinding process for completely removing the space holder was proposed. Finally, the shrinkage and porosity of the tensile specimen produced through the sintering process were analyzed and the ultimate tensile strength was obtained. Full article
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Open AccessArticle Influence of NbC Addition on the Sintering Behaviour of Medium Carbon PM Steels
Metals 2017, 7(4), 121; doi:10.3390/met7040121
Received: 9 February 2017 / Revised: 27 March 2017 / Accepted: 28 March 2017 / Published: 1 April 2017
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Abstract
In this work, the effects of NbC additions on the microstructure and mechanical properties were examined. In order to do this, NbC compounds were added into the Fe matrix at the weight percentage of 0.1–2 with individually to obtain powder mixture. The microstructure
[...] Read more.
In this work, the effects of NbC additions on the microstructure and mechanical properties were examined. In order to do this, NbC compounds were added into the Fe matrix at the weight percentage of 0.1–2 with individually to obtain powder mixture. The microstructure of the powder metallurgy (PM) steels were characterized by optic microscope, scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS). Experimental results indicated that NbC alloyed steels can be produced by PM technology. An increase in strength was observed when the amount of NbC compounds increased for all PM steels. The precipitation of carbides and nitrides in these steels limits austenite grain growth and increases the precipitation hardening or clustering hardening that results in significant improvement in strength. Full article
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Open AccessArticle Pyroelectrically Induced Pyro-Electro-Chemical Catalytic Activity of BaTiO3 Nanofibers under Room-Temperature Cold–Hot Cycle Excitations
Metals 2017, 7(4), 122; doi:10.3390/met7040122
Received: 1 March 2017 / Revised: 24 March 2017 / Accepted: 27 March 2017 / Published: 1 April 2017
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Abstract
A pyro-electro-chemical catalytic dye decomposition using lead-free BaTiO3 nanofibers was realized under room-temperature cold–hot cycle excitation (30–47 °C) with a high Rhodamine B (RhB) decomposition efficiency ~99%, which should be ascribed to the product of pyro-electric effect and electrochemical redox reaction. Furthermore,
[...] Read more.
A pyro-electro-chemical catalytic dye decomposition using lead-free BaTiO3 nanofibers was realized under room-temperature cold–hot cycle excitation (30–47 °C) with a high Rhodamine B (RhB) decomposition efficiency ~99%, which should be ascribed to the product of pyro-electric effect and electrochemical redox reaction. Furthermore, the existence of intermediate product of hydroxyl radical in pyro-electro-chemical catalytic process was also observed. There is no significant decrease in pyro-electro-chemical catalysis activity after being recycled five times. The pyro-electrically induced pyro-electro-chemical catalysis provides a high-efficient, reusable and environmentally friendly technology to remove organic pollutants from water. Full article
(This article belongs to the Special Issue Piezoelectric Materials and Applications)
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Open AccessArticle Structural Investigations of TiC–Cu Nanocomposites Prepared by Ball Milling and Spark Plasma Sintering
Metals 2017, 7(4), 123; doi:10.3390/met7040123
Received: 17 January 2017 / Revised: 10 March 2017 / Accepted: 31 March 2017 / Published: 3 April 2017
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Abstract
In this work, TiC–Cu composites containing 20 and 30 vol % of nano-sized titanium carbide (TiC) particles were prepared by powder metallurgy using copper powders with micrometer-sized and nanometer-sized particles. Mixtures of TiC and Cu powders were ball milled for 10 h and
[...] Read more.
In this work, TiC–Cu composites containing 20 and 30 vol % of nano-sized titanium carbide (TiC) particles were prepared by powder metallurgy using copper powders with micrometer-sized and nanometer-sized particles. Mixtures of TiC and Cu powders were ball milled for 10 h and spark plasma sintered at 800–900 °C under an applied pressure of 50 MPa. The relative density of the sintered composites was 95.0%–96.5%. The composites fractured in a ductile mode. The crystallite size of the copper matrix in the composites prepared using the nanometer-sized copper powder was smaller than that in composites prepared using the micrometer-sized copper powder, which was confirmed by transmission electron microscopy (TEM). The hardness of the composites increased as the sintering temperature was increased from 800 to 900 °C. When the TiC content increased from 20 to 30 vol %, the hardness of the composites obtained from the micrometer-sized copper powder and sintered at 900 °C increased from 284 to 315 HV, while in composites obtained from the nanometer-sized copper, the hardness decreased from 347 to 337 HV. Full article
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Open AccessArticle Efficient Use of Porous Hybrid Materials in a Selective Detection of Lead(II) from Aqueous Solutions: An Electrochemical Study
Metals 2017, 7(4), 124; doi:10.3390/met7040124
Received: 6 January 2017 / Revised: 20 February 2017 / Accepted: 28 March 2017 / Published: 20 April 2017
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Abstract
Due to health and pollution concerns of aquatic environments related to the presence of heavy metal toxic ions, the necessity of developing devices able to detect and to monitor such kinds of species has recently gained importance. Carbon paste electrodes (CPEs) a starting
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Due to health and pollution concerns of aquatic environments related to the presence of heavy metal toxic ions, the necessity of developing devices able to detect and to monitor such kinds of species has recently gained importance. Carbon paste electrodes (CPEs) a starting approach to obtain new ion-selective devices by supporting materials like bentonite and/or clay; which become sensitive to lead(II) when they are suitably modified by chemical treatments to obtain different hybrid materials. In this work, two natural clays and three different hybrid materials were produced and then were characterized by X-ray diffraction, scanning electron microscopy, and Fourier transform infrared spectroscopy to assess their physico-chemical properties. After this stage, the electrochemical characterization of the modified CPEs using hybrid materials was performed by cyclic voltammetry, using the standard Fe(CN)64−/Fe(CN)63− redox couple. Subsequently, this study performed electrochemical experiments on lead(II) containing solutions, to test the ability of the examined CPEs to detect this toxic ion present in very low amounts. Lead(II) exhibited a reversible two electron oxidation/reduction behaviour in the cyclic voltammetry analyses and a reasonably good linear behaviour of the current associated with the oxidation peak as a function of its concentration (5.0–40.0 μg/L). The detection limit was found to vary in the range of 3–5 μg/L for the different modified CPEs. The presence of several co-existing ions showed that an interference variation had occurred. These results, therefore, show a restriction of the selectivity of the electrode up to a certain extent in the lead(II) detection. Finally, tap water with spiked lead(II) was analyzed to verify the suitability of the electrodes in the low level detection of lead(II) from real matrix samples. Full article
(This article belongs to the Special Issue Heavy Metal Determination and Removal)
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Open AccessArticle Microstructural Characteristics and Mechanical Properties of 2205/AZ31B Laminates Fabricated by Explosive Welding
Metals 2017, 7(4), 125; doi:10.3390/met7040125
Received: 26 February 2017 / Revised: 24 March 2017 / Accepted: 28 March 2017 / Published: 4 April 2017
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Abstract
A bimetal composite of 2205 duplex stainless steel and AZ31B magnesium alloy was cladded successfully through the method of explosive welding. The microstructural characteristics and mechanical properties of 2205/AZ31B bimetal composite are discussed. The interface of 2205/AZ31B bimetallic composite was a less regular
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A bimetal composite of 2205 duplex stainless steel and AZ31B magnesium alloy was cladded successfully through the method of explosive welding. The microstructural characteristics and mechanical properties of 2205/AZ31B bimetal composite are discussed. The interface of 2205/AZ31B bimetallic composite was a less regular wavy morphology with locally melted pockets. Adiabatic shear bands occurred only in the AZ31B side near explosive welding interface. The microstructure observed with EBSD showed a strong refinement near the interface zones. Line scan confirmed that the interface had a short element diffusion zone which would contribute to the metallurgical bonding between 2205 duplex stainless steel and AZ31B magnesium alloy. The value of micro-hardness near the bonding interface of composite plate increased because of work hardening and grain refinement. The tensile shear strength of bonding interface of 2205/AZ31B composite was 105.63 MPa. Tensile strength of 2205/AZ31B composite material was higher than the base AZ31B. There were two abrupt drops in stress in the stress–strain curves of the 2205/AZ31B composite materials. Full article
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Open AccessArticle Experimental Analysis of the Behaviour of Aluminium Alloy EN 6082AW T6 at High Temperature
Metals 2017, 7(4), 126; doi:10.3390/met7040126
Received: 13 February 2017 / Revised: 13 March 2017 / Accepted: 1 April 2017 / Published: 4 April 2017
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Abstract
The paper presents test results for the mechanical and creep properties of European aluminium alloy EN 6082AW T6 at high temperatures. Mechanical properties of the aluminium alloy were determined by means of two types of test: constant stress-rate and stationary creep tests. Mechanical
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The paper presents test results for the mechanical and creep properties of European aluminium alloy EN 6082AW T6 at high temperatures. Mechanical properties of the aluminium alloy were determined by means of two types of test: constant stress-rate and stationary creep tests. Mechanical properties were determined up to a temperature of 350 °C, while the creep tests were conducted within the temperature interval 150–300 °C. The creep tests conducted identified the critical temperature interval for creep development, which represents an important factor when analysing creep behaviour of aluminium structures. This temperature interval was found to be within the range 200–300 °C. Test results for stress at 0.2% strain and modulus of elasticity at different temperatures showed good agreement with the codified values from Eurocode 9 and with other comparable studies. Full article
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Open AccessArticle Preparation and Properties of Microarc Oxidation Self-Lubricating Composite Coatings on Aluminum Alloy
Metals 2017, 7(4), 127; doi:10.3390/met7040127
Received: 22 January 2017 / Revised: 22 March 2017 / Accepted: 28 March 2017 / Published: 5 April 2017
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Abstract
Microarc oxidation (MAO) coatings were prepared on 2024-T4 aluminum alloy using pulsed bipolar power supply at different cathode current densities. The MAO ceramic coatings contained many crater-like micropores and a small number of microcracks. After the MAO coatings were formed, the coated samples
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Microarc oxidation (MAO) coatings were prepared on 2024-T4 aluminum alloy using pulsed bipolar power supply at different cathode current densities. The MAO ceramic coatings contained many crater-like micropores and a small number of microcracks. After the MAO coatings were formed, the coated samples were immersed into a water-based Polytetrafluoroethylene (PTFE) dispersion. The micropores and microcracks on the surface of the MAO coatings were filled with PTFE dispersion for preparing MAO self-lubricating composite coatings. The microstructure and properties of MAO coatings and the wear resistance of microarc oxidation self-lubricating composite coatings were analyzed by SEM, laser confocal microscope, X-ray diffractometry (XRD), Vickers hardness test, scratch test and ball-on-disc abrasive tests, respectively. The results revealed that the wear rates of the MAO coatings decreased significantly with an increase in cathode current density. Compared to the MAO coatings, the microarc oxidation self-lubricating composite coatings exhibited a lower friction coefficient and lower wear rates. Full article
(This article belongs to the Special Issue Metallic and Metal Oxide Nanoparticles: Novel Approaches)
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Open AccessArticle A Non-Destructive Technique for the On-Line Quality Control of Green and Baked Anodes †
Metals 2017, 7(4), 128; doi:10.3390/met7040128
Received: 13 February 2017 / Revised: 27 March 2017 / Accepted: 1 April 2017 / Published: 6 April 2017
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Abstract
Carbon anodes play an important role in the electrolytic production of aluminum. They have a significant economic and environmental impact. Carbon anodes are made of dry aggregates, composed of petroleum coke, recycled rejects, and butts, bound by coal tar pitch. Due to several
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Carbon anodes play an important role in the electrolytic production of aluminum. They have a significant economic and environmental impact. Carbon anodes are made of dry aggregates, composed of petroleum coke, recycled rejects, and butts, bound by coal tar pitch. Due to several factors, defects (cracks/pores) appear in anodes during the fabrication process, affecting their quality. It is thus essential to control the quality of anodes before their use in the electrolysis cell. Current practice for the quality evaluation (visual inspection, core analysis) gives limited information. As an alternative to this practice, electrical resistivity measurements can be used. Electrical resistivity is one of the key indicators for anode quality and its homogeneity. A simple and non-destructive method has been developed for the specific electrical resistivity measurement of anodes (SERMA) for on-line control of anode quality. Various tests have been carried out at both lab scale and industrial scale. In this study, the electrical resistivity distributions in the lab-scale anodes were measured and compared with those of the tomography analysis. The method is able to detect defective anodes even before the baking process. Full article
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Open AccessArticle The Influence of FeO on the Reaction between Fe–Al–Ca Alloy and Al2O3–CaO–FeO Oxide during Heat Treatment at 1473 K
Metals 2017, 7(4), 129; doi:10.3390/met7040129
Received: 12 March 2017 / Revised: 29 March 2017 / Accepted: 5 April 2017 / Published: 7 April 2017
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Abstract
Oxygen diffusion from oxides to an alloy during heat treatment could influence the properties of the alloy and oxides. To clarify the influence of FeO on the solid-state reactions between Al2O3–CaO–FeO oxide and Fe–Al–Ca alloy during heat treatment at
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Oxygen diffusion from oxides to an alloy during heat treatment could influence the properties of the alloy and oxides. To clarify the influence of FeO on the solid-state reactions between Al2O3–CaO–FeO oxide and Fe–Al–Ca alloy during heat treatment at 1473 K, three diffusion couples with different FeO concentrations in the oxide were produced. The diffusion couples were subjected to several procedures successively including an oxide pre-melting experiment using a confocal scanning laser microscope to obtain good contact between the alloy and oxide, vacuum sealing to protect the specimens from oxidation, heat treatment, and electron probe X-ray microanalysis. The effects of the FeO content in the oxide on the morphology of the interface between the alloy and oxide, change of elements in the alloy, widths of the particle precipitation zone (PPZ) and aluminum-depleted zone (ADZ), and size distribution of the particles in the alloy, were investigated and discussed. Based on the Wagner equation of internal oxidation of metals, a modified dynamic model to calculate the PPZ width was established to help understand the mechanism of the solid-state reactions and element diffusion between the Fe–Al–Ca alloy and Al2O3–CaO–FeO oxide with different FeO concentrations. Full article
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Open AccessArticle Heating System for Riser Size Minimizing in Sand Casting Process and Its Experimental Verification
Metals 2017, 7(4), 130; doi:10.3390/met7040130
Received: 28 February 2017 / Revised: 26 March 2017 / Accepted: 4 April 2017 / Published: 8 April 2017
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Abstract
In the conventional sand casting process, the size of the riser is made larger than that of the cavity (product part) in order for the molten metal in the riser to solidify at a later stage than the molten metal in the cavity.
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In the conventional sand casting process, the size of the riser is made larger than that of the cavity (product part) in order for the molten metal in the riser to solidify at a later stage than the molten metal in the cavity. In this study, a continuous heating method is developed and applied to the riser, using a cylindrical heater, to minimize the size of the riser. A mold having four cavities is designed for casting turbine housings. The height and diameter of the riser are chosen to be 80 mm and 20 mm, respectively. Solidification analysis results, using the analysis program MAGMA soft for casting simulation, showed that when the heater is implemented, the riser is the last to solidify. However, without the heater, the riser solidifies before the cavity, thus causing the riser to function improperly. Moreover, misruns are generated in the casted product if the heater is not implemented, as opposed to the case of a solid product without any defects, with the heater attached in the riser. Full article
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Open AccessArticle Microstructure, Texture Evolution and Mechanical Properties of VT3-1 Titanium Alloy Processed by Multi-Pass Drawing and Subsequent Isothermal Annealing
Metals 2017, 7(4), 131; doi:10.3390/met7040131
Received: 22 March 2017 / Revised: 31 March 2017 / Accepted: 3 April 2017 / Published: 10 April 2017
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Abstract
Microstructure, texture evolution, and mechanical properties of Ti–6Al–1.5Cr–2.5Mo–0.5Fe–0.3Si (VT3-1) titanium alloy processed by multi-pass drawing and subsequent isothermal annealing were systematically investigated. A fiber-like microstructure is formed after warm drawing at 760 °C with 60% area reduction. After isothermal annealing, the samples deformed
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Microstructure, texture evolution, and mechanical properties of Ti–6Al–1.5Cr–2.5Mo–0.5Fe–0.3Si (VT3-1) titanium alloy processed by multi-pass drawing and subsequent isothermal annealing were systematically investigated. A fiber-like microstructure is formed after warm drawing at 760 °C with 60% area reduction. After isothermal annealing, the samples deformed to different amounts of area reduction show a similar volume fraction (80%) of α phase, while the sample deformed to 60% exhibits a homogeneous microstructure with a larger grain size (5.8 μm). The major texture component of α phase developed during warm drawing is centered at a position of {φ1 = 10°, φ = 65°, φ2 = 0°}. The textures for annealed samples are almost along the orientation of original deformation textures and show significant increases in orientation density and volume fraction compared with their deformed states. In addition, for the drawn samples, the ultimate tensile strength increases but the ductility decreases with increasing drawing deformation. A negative slope of yield strength of annealed samples versus grain size (d−1/2) is found due to the difference between texture softening for as-rolled + annealed state and texture hardening for drawn + annealed state. The mechanical properties of annealed samples are found to be strongly dependent on grain size and texture, resulting in the balance of the strength and ductility. Full article
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Open AccessArticle Effect of the Impeller Design on Degasification Kinetics Using the Impeller Injector Technique Assisted by Mathematical Modeling
Metals 2017, 7(4), 132; doi:10.3390/met7040132
Received: 16 February 2017 / Revised: 22 March 2017 / Accepted: 24 March 2017 / Published: 10 April 2017
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Abstract
A mathematical model was developed to describe the hydrodynamics of a batch reactor for aluminum degassing utilizing the rotor-injector technique. The mathematical model uses the Eulerian algorithm to represent the two-phase system including the simulation of vortex formation at the free surface, and
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A mathematical model was developed to describe the hydrodynamics of a batch reactor for aluminum degassing utilizing the rotor-injector technique. The mathematical model uses the Eulerian algorithm to represent the two-phase system including the simulation of vortex formation at the free surface, and the use of the RNG k-ε model to account for the turbulence in the system. The model was employed to test the performances of three different impeller designs, two of which are available commercially, while the third one is a new design proposed in previous work. The model simulates the hydrodynamics and consequently helps to explain and connect the performances in terms of degassing kinetics and gas consumption found in physical modeling previously reported. Therefore, the model simulates a water physical model. The model reveals that the new impeller design distributes the bubbles more uniformly throughout the ladle, and exhibits a better-agitated bath, since the transfer of momentum to the fluids is better. Gas is evenly distributed with this design because both phases, gas and liquid, are dragged to the bottom of the ladle as a result of the higher pumping effect in comparison to the commercial designs. Full article
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Open AccessArticle High-Cycle Microscopic Severe Corrosion Fatigue Behavior and Life Prediction of 25CrMo Steel Used in Railway Axles
Metals 2017, 7(4), 134; doi:10.3390/met7040134
Received: 18 January 2017 / Revised: 28 March 2017 / Accepted: 7 April 2017 / Published: 11 April 2017
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Abstract
The effects of environmental media on the corrosion fatigue fracture behavior of 25CrMo steel were investigated. The media include air, and 3.5 wt % and 5.0 wt % NaCl solutions. Experimental results indicate that the media induces the initiation of corrosion fatigue cracks
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The effects of environmental media on the corrosion fatigue fracture behavior of 25CrMo steel were investigated. The media include air, and 3.5 wt % and 5.0 wt % NaCl solutions. Experimental results indicate that the media induces the initiation of corrosion fatigue cracks at multiple sites. The multi-cracking sites cause changes in the crack growth directions, the crack growth rate during the coupling action of the media, and the stress amplitude. The coupling effects are important for engineering applications and research. The probability and predictions of the corrosion fatigue characteristic life can be estimated using the three-parameter Weibull distribution function. Full article
(This article belongs to the Special Issue Fatigue Damage)
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Open AccessArticle Face Centred Cubic Multi-Component Equiatomic Solid Solutions in the Au-Cu-Ni-Pd-Pt System
Metals 2017, 7(4), 135; doi:10.3390/met7040135
Received: 20 December 2016 / Revised: 2 March 2017 / Accepted: 6 April 2017 / Published: 12 April 2017
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Abstract
A single-phase solid solution is observed in quaternary and quinary alloys obtained from gold, copper, nickel, palladium and platinum. The lattice parameters of the alloys follow the linear rule of mixture when considering the lattice parameters of the elements and their concentration. The
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A single-phase solid solution is observed in quaternary and quinary alloys obtained from gold, copper, nickel, palladium and platinum. The lattice parameters of the alloys follow the linear rule of mixture when considering the lattice parameters of the elements and their concentration. The elements are a priori not homogeneously distributed within the respective alloys resulting in segregations. These segregations cause a large broadening of X-ray lines, which is accessed in the present article. This correlation is visualized by the help of local element mappings utilizing scanning electron microscopy including energy dispersive X-ray analysis and their quantitative analysis. Full article
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Open AccessArticle Residual Stresses with Time-Independent Cyclic Plasticity in Finite Element Analysis of Welded Joints
Metals 2017, 7(4), 136; doi:10.3390/met7040136
Received: 21 December 2016 / Revised: 5 April 2017 / Accepted: 6 April 2017 / Published: 13 April 2017
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Abstract
Due to the intense concentration of heat in a reduced area when Gas Metal Arc Welding (GMAW) is used to join mechanical components, the regions near the weld bead are subjected to severe thermal cycles. Firstly, the region close to the weld bead
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Due to the intense concentration of heat in a reduced area when Gas Metal Arc Welding (GMAW) is used to join mechanical components, the regions near the weld bead are subjected to severe thermal cycles. Firstly, the region close to the weld bead that is heated tends to be in compression and, when it cools, tends to be in tension. According to Pilipenko, the material is exposed to elastic compression and, then, reaching the yield limit, undergoes plastic deformation with the appearance of residual stresses followed by elastic-plastic unloading. This could be considered as a strain-stress cycle. This paper applies plastic-strain-range memorization based on time-independent cyclic plasticity theory for butt joints with single V-groove Finite Element (FE) models that were manufactured by GMAW. The theory combines both the isotropic hardening and the nonlinear kinematic hardening rule (Chaboche model) to reproduce the behavior of cyclic plasticity and thus to obtain the residual stresses in welded joint FE models. As a practical example, the proposed theory is validated by three welded joint specimens that were manufactured with different input parameters of speed, voltage, and current. An agreement between the residual stresses obtained by the FE model proposed and those obtained experimentally by the hole drilling method at different depths demonstrates that the proposed theory could be valid for modelling the residual stresses in welded joints when cyclic plasticity is considered over the range of speed, voltage, and current studied. Full article
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Open AccessArticle Improved Solar Absorptance of WC/Co Solar Selective Absorbing Coating with Multimodal WC Particles
Metals 2017, 7(4), 137; doi:10.3390/met7040137
Received: 19 January 2017 / Revised: 29 March 2017 / Accepted: 7 April 2017 / Published: 13 April 2017
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Abstract
One type of multimodal (comprised of nanometer and sub-micrometer WC particles) and two types of conventional (comprised of nanometer and sub-micrometer WC particles, respectively) WC/Co powders were deposited on AISI 304L stainless steel substrates by using high velocity oxygen fuel spraying. The use
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One type of multimodal (comprised of nanometer and sub-micrometer WC particles) and two types of conventional (comprised of nanometer and sub-micrometer WC particles, respectively) WC/Co powders were deposited on AISI 304L stainless steel substrates by using high velocity oxygen fuel spraying. The use of multimodal WC particles was indicated to have a beneficial effect on the solar absorptance (α) of the WC/Co coatings. The α of the multimodal WC coating reached 0.87, which was much higher than what can be achieved by either fine (0.82) or coarse powders (0.80) alone. By microstructural analysis, the enhancement in solar absorptance of the multimodal WC/Co coating was ascribed to the layer of distributed WC particles. During the thermal spraying, the nanostructured WC particles underwent rapid melting for the large specific surface area while the aggregated powders were heated, but not necessarily melted. The molten nano-WC would fill the available pores between the softened and heated aggregates, providing a layered distribution of WC particles for the spray-deposited coating. In this condition, the light-trapping in the multimodal coating will be enhanced due to the efficient light reflection among the multimodal WC particles, which contributes to the enhancement of solar absorptance. Full article
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Open AccessArticle Characterization of the Microstructure, Mechanical Properties, and Corrosion Resistance of a Friction-Stir-Welded Joint of Hyper Duplex Stainless Steel
Metals 2017, 7(4), 138; doi:10.3390/met7040138
Received: 10 January 2017 / Revised: 31 March 2017 / Accepted: 5 April 2017 / Published: 13 April 2017
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Abstract
This study investigates the microstructure, mechanical properties, and corrosion resistance of a friction-stir-welded joint of the hyper duplex stainless steel SAF2707. Friction stir welding (FSW) is performed at a tool rotation rate of 400 rpm and a welding speed of 100 mm/min. The
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This study investigates the microstructure, mechanical properties, and corrosion resistance of a friction-stir-welded joint of the hyper duplex stainless steel SAF2707. Friction stir welding (FSW) is performed at a tool rotation rate of 400 rpm and a welding speed of 100 mm/min. The microstructure of the joints is examined using scanning electron microscopy and X-ray diffraction. Tensile test and fractography are subsequently employed to evaluate the mechanical properties of the joints. Results show that the grain size of the stir zone (SZ) is smaller than that of the base metal (BM). Electron back-scattered diffraction analysis reveals that fine-equiaxed grains form in the SZ because of the dynamic recrystallization during the FSW. These grains become increasingly pronounced in the austenite phase. The tensile specimens consistently fail in the BM, implying that the welded joint is an overmatch to the BM. Moreover, the welded joints consist of finer grains and thus display higher tensile strength than their BMs. Potentiodynamic polarization curves and impedance spectroscopy both demonstrate that the corrosion resistance of the SZ is superior to that of the base material. Full article
(This article belongs to the Special Issue Alloy Steels)
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Open AccessArticle Tribological Properties of Plough Shares Made of Pearlitic and Martensitic Steels
Metals 2017, 7(4), 139; doi:10.3390/met7040139
Received: 11 March 2017 / Revised: 5 April 2017 / Accepted: 11 April 2017 / Published: 14 April 2017
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Abstract
Tribological properties of ploughshares made of pearlitic and martensitic steels were compared in field tests. Sectional ploughshares consisting of separate share-points and trapezoidal parts were subjected to examinations. Contours of the examined parts were similar, but the thickness of the parts made of
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Tribological properties of ploughshares made of pearlitic and martensitic steels were compared in field tests. Sectional ploughshares consisting of separate share-points and trapezoidal parts were subjected to examinations. Contours of the examined parts were similar, but the thickness of the parts made of pearlitic steel was 1 to 3 mm greater for the share-points and 0.5 to 2 mm greater for the trapezoidal parts. Within the tests, sandy loams, loams, and loamy sands with circa (ca.) 13% humidity were cultivated. A greater intensity of thickness reduction and mass wear of the parts made of pearlitic steel was found, which indicates a lower resistance of this steel to wear in soil. However, contour changes of the share-points and the trapezoidal parts made of pearlitic and martensitic steels were comparable, which was probably influenced by the greater thickness of the parts made of pearlitic steel. The roughness of the rake faces of the parts made of pearlitic steel was greater than that for the parts made of martensitic steel, which can be attributed to lower hardness of the former. The largest differences occurred between maximum peak heights of the roughness profile values (Rp), which indicates stronger ridging in the case of pearlitic steel. Scanning electron microscope (SEM) observations of the rake faces showed that martensitic steel was subjected to wear mostly by microcutting, but pearlitic steel was principally worn by microcutting and microploughing. During tillage, only one share-point made of pearlitic steel was broken. However, the main disadvantage of these parts was that their bending was related to the lower mechanical strength of pearlitic steel. Full article
(This article belongs to the Special Issue Alloy Steels)
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Open AccessArticle Advanced Plasticity Modeling for Ultra-Low-Cycle-Fatigue Simulation of Steel Pipe
Metals 2017, 7(4), 140; doi:10.3390/met7040140
Received: 5 March 2017 / Revised: 11 April 2017 / Accepted: 13 April 2017 / Published: 14 April 2017
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Abstract
Pipelines and piping components may be exposed to extreme loading conditions, for instance earthquakes and hurricanes. In such conditions, they undergo severe plastic strains, which may locally reach the fracture limits due to either monotonic loading or ultra-low cycle fatigue (ULCF). Aiming to
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Pipelines and piping components may be exposed to extreme loading conditions, for instance earthquakes and hurricanes. In such conditions, they undergo severe plastic strains, which may locally reach the fracture limits due to either monotonic loading or ultra-low cycle fatigue (ULCF). Aiming to investigate the failure process and strain evolution of pipes enduring ULCF, a lab-scale ULCF test on an X65 steel pipeline component is simulated with finite element models, and experimental data are used to validate various material modeling assumptions. The paper focuses on plastic material modeling and compares different models for plastic anisotropy in combination with various hardening models, including isotropic, linear kinematic and combined hardening models. Both isotropic and anisotropic assumptions for plastic yielding are considered. As pipes pose difficulty for the measurement of plastic properties in mechanical testing, we calibrate an anisotropic yield locus using advanced multi-scale simulation based on texture measurements. Moreover, the importance of the anisotropy gradient across thickness is studied in detail for this thick-walled pipeline steel. It is found that the usage of a combined hardening model is essential to accurately predict the number of the cycles until failure, as well as the strain evolution during the fatigue test. The advanced hardening modeling featuring kinematic hardening has a substantially higher impact on result accuracy compared to the yield locus assumption for the studied ULCF test. Cyclic tension-compression testing is conducted to calibrate the kinematic hardening models. Additionally, plastic anisotropy and its gradient across the thickness play a notable, yet secondary role. Based on this research, it is advised to focus on improvements in strain hardening characteristics in future developments of pipeline steel with enhanced earthquake resistance. Full article
(This article belongs to the Special Issue Advances in Plastic Forming of Metals)
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Open AccessFeature PaperArticle Dynamic Recovery and Superelasticity of Columnar-Grained Cu–Al–Mn Shape Memory Alloy
Metals 2017, 7(4), 141; doi:10.3390/met7040141
Received: 23 March 2017 / Revised: 9 April 2017 / Accepted: 11 April 2017 / Published: 15 April 2017
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Abstract
The columnar-grained Cu71.5Al17.5Mn11 shape memory alloy was treated by single-pass hot rolling at 900 °C with a thickness reduction of 67.3% followed by immediate water quenching. Dynamic recovery other than discontinuous dynamic recrystallization occurred during the treatment process,
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The columnar-grained Cu71.5Al17.5Mn11 shape memory alloy was treated by single-pass hot rolling at 900 °C with a thickness reduction of 67.3% followed by immediate water quenching. Dynamic recovery other than discontinuous dynamic recrystallization occurred during the treatment process, bringing about retained columnar grains with <001> textures, as well as dislocations introduced into the parent matrix. As a result, a large maximum recoverable strain of more than 11% was maintained due to the retained beneficial grain characteristics. The critical stress for inducing martensitic transformation and stress hysteresis were enhanced mainly due to the existence of dislocations. Full article
(This article belongs to the Special Issue Shape Memory Alloys 2017)
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Open AccessArticle Synthesis and Characterization of Nano-Particles of Niobium Pentoxide with Orthorhombic Symmetry
Metals 2017, 7(4), 142; doi:10.3390/met7040142
Received: 27 March 2017 / Revised: 10 April 2017 / Accepted: 13 April 2017 / Published: 19 April 2017
PDF Full-text (831 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
In this work, a set of nanoparticles of Nb2O5 nanoparticles were grown by both the Pechini and the sol-gel methods. The amorphous materials were calcined at 650 #xB0;C or at 750 °C. X-ray diffraction, scanning electron microscopy, luminescence and Raman
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In this work, a set of nanoparticles of Nb2O5 nanoparticles were grown by both the Pechini and the sol-gel methods. The amorphous materials were calcined at 650 #xB0;C or at 750 °C. X-ray diffraction, scanning electron microscopy, luminescence and Raman spectroscopy were used in order to characterize the materials. From the study, it is possible to state that the method of production of nanoparticles, beyond the temperature of synthesis, has a great influence on whether the phase produced is hexagonal or orthorhombic. Additionally, compared to de Sol-gel method, the Pechini method produced samples with smaller particle sizes. The photoluminescence spectra of niobium pentoxide nanostructure materials show that the emission peaks are positioned between 334 to 809 nm and there is a change of intensity which varies depending on the synthesis route used. High pressure Raman spectra at room temperature were obtained from two samples grown by the sol-gel method. Up to 6 GPa, where it is possible to observe the Raman bands, no modification other than the increase of disorder was observed, and this can be associated with a change of phase. Full article
(This article belongs to the Special Issue Synthesis and Properties of Bulk Nanostructured Metallic Materials)
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Open AccessArticle Vickers Indentation Fracture Toughness of Near-Nano and Nanostructured WC-Co Cemented Carbides
Metals 2017, 7(4), 143; doi:10.3390/met7040143
Received: 13 January 2017 / Revised: 1 April 2017 / Accepted: 12 April 2017 / Published: 19 April 2017
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Abstract
In this paper, the fracture toughness KIc of near-nano and nanostructured WC-Co cemented carbides by Vickers indentation fracture toughness (VIF) was investigated. The aim was to research the type of cracking occurring in near-nano and nano-grained WC-Co cemented carbides with respect to
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In this paper, the fracture toughness KIc of near-nano and nanostructured WC-Co cemented carbides by Vickers indentation fracture toughness (VIF) was investigated. The aim was to research the type of cracking occurring in near-nano and nano-grained WC-Co cemented carbides with respect to the Co content and, consequently, to evaluate the appropriateness of different models for the fracture toughness calculation. The mixtures with different binder content—4, 6, and 9 wt. % Co—were consolidated by sintering in a hydrogen atmosphere. Vickers indentation using a test force of 294 N was used for the determination of fracture toughness. The type of crack that occurred as a consequence of the applied load on the corners of the Vickers indentations was analysed with optical microscopy before and after repolishing the samples. Different crack models, Palmqvist and radial-median, were applied for the calculation of KIc. Instrumented indentation testing was used to determine the modulus of elasticity of the consolidated samples. From the research it was found that near-nano and nanostructured cemented carbides with 9 and 6 wt. % Co do not exhibit median cracking and the indenter cracks remain radial in nature, while near-nano and nanostructured cemented carbides with 4 wt. % Co exhibit both radial and median cracking. Accordingly, it was concluded that the critical amount of the binder phase in near-nano and nanostructured WC-Co at which the crack changes its geometry from Palmqvist to radial-median is around 4 wt. % Co. Comparing different models it was found that KIc values are not consistent and differ for each method used. Models from Exner crack resistance for the Palmqvist crack showed good agreement. Radial-median crack models showed significant KIc deviations for the same testing conditions for all samples. Full article
(This article belongs to the Special Issue Cermets and Hardmetals)
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Open AccessArticle New Low-Sn Zr Cladding Alloys with Excellent Autoclave Corrosion Resistance and High Strength
Metals 2017, 7(4), 144; doi:10.3390/met7040144
Received: 21 March 2017 / Revised: 12 April 2017 / Accepted: 17 April 2017 / Published: 19 April 2017
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Abstract
It is expected that low-Sn Zr alloys are a good candidate to improve the corrosion resistance of Zr cladding alloys in nuclear reactors, presenting excellent corrosion resistance and high strength. The present work developed a new alloy series of Zr-0.25Sn-0.36Fe-0.11Cr-xNb (
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It is expected that low-Sn Zr alloys are a good candidate to improve the corrosion resistance of Zr cladding alloys in nuclear reactors, presenting excellent corrosion resistance and high strength. The present work developed a new alloy series of Zr-0.25Sn-0.36Fe-0.11Cr-xNb (x = 0.4~1.2 wt %) to investigate the effect of Nb on autoclave corrosion resistance. Alloy ingots were prepared by non-consumable arc-melting, solid-solutioned, and then rolled into thin plates with a thickness of 0.7 mm. It was found that the designed low-Sn Zr alloys exhibit excellent corrosion resistances in three out of pile autoclave environments (distilled water at 633 K/18.6 MPa, 70 ppm LiOH solution at 633 K/18.6 MPa, and superheated water steam at 673 K/10.3 MPa), as demonstrated by the fact of the Zr-0.25Sn-0.36Fe-0.11Cr-0.6Nb alloy shows a corrosion weight gain ΔG = 46.3 mg/dm2 and a tensile strength of σUTS = 461 MPa following 100 days of exposure in water steam. The strength of the low-Sn Zr alloy with a higher Nb content (x = 1.2 wt %) is enhanced up to 499 MPa, comparable to that of the reference high-Sn N36 alloy (Zr-1.0Sn-1.0Nb-0.25Fe, wt %). Although the strength improvement is at a slight expense of corrosion resistance with the increase of Nb, the corrosion resistance of the high-Nb alloy with x = 1.2 (ΔG = 90.4 mg/dm2 for 100-day exposure in the water steam) is still better than that of N36 (ΔG = 103.4 mg/dm2). Full article
(This article belongs to the Special Issue Zirconium Alloys)
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Open AccessArticle Role of Severe Plastic Deformation in Suppressing Formation of R Phase and Ni4Ti3 Precipitate of NiTi Shape Memory Alloy
Metals 2017, 7(4), 145; doi:10.3390/met7040145
Received: 22 March 2017 / Revised: 14 April 2017 / Accepted: 17 April 2017 / Published: 19 April 2017
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Abstract
Microstructural evolution of NiTi shape memory alloy (SMA) with a nominal composition of Ni50.9Ti49.1 (at %) is investigated on the basis of heat treatment and severe plastic deformation (SPD). As for as-rolled NiTi SMA samples subjected to aging, plenty of
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Microstructural evolution of NiTi shape memory alloy (SMA) with a nominal composition of Ni50.9Ti49.1 (at %) is investigated on the basis of heat treatment and severe plastic deformation (SPD). As for as-rolled NiTi SMA samples subjected to aging, plenty of R phases appear in the austenite matrix. In terms of as-rolled NiTi SMA samples undergoing solution treatment and aging, Ni4Ti3 precipitates arise in the austenite matrix. In the case of as-rolled NiTi SMA samples subjected to SPD and aging, martensitic twins are observed in the matrix of NiTi SMA. With respect to as-rolled NiTi SMA samples subjected to solution treatment, SPD, and aging, neither R phases nor Ni4Ti3 precipitates are observed in the matrix of NiTi SMA. The dislocation networks play an important role in the formation of the R phase. SPD leads to amorphization of NiTi SMA, and in the case of annealing, amorphous NiTi SMA samples are subjected to crystallization. This contributes to suppressing the occurrence of R phase and Ni4Ti3 precipitate in NiTi SMA. Full article
(This article belongs to the Special Issue Shape Memory Alloys 2017)
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Open AccessArticle The Effects of a Submerged Entry Nozzle on Flow and Initial Solidification in a Continuous Casting Bloom Mold with Electromagnetic Stirring
Metals 2017, 7(4), 146; doi:10.3390/met7040146
Received: 24 February 2017 / Revised: 15 April 2017 / Accepted: 17 April 2017 / Published: 19 April 2017
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Abstract
The melt flow, level fluctuation, temperature field, and solidification behavior coupled with electromagnetic stirring (EMS) effects in the continuous casting mold region of U71Mn steel bloom were numerically analyzed by commercial computational fluid dynamics (CFD) software named ANSYS FLUENT. The effects of submerged
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The melt flow, level fluctuation, temperature field, and solidification behavior coupled with electromagnetic stirring (EMS) effects in the continuous casting mold region of U71Mn steel bloom were numerically analyzed by commercial computational fluid dynamics (CFD) software named ANSYS FLUENT. The effects of submerged entry nozzle (SEN) structures and the installation methods for optimized four-port SEN on the flow pattern, level fluctuation, heat transfer and initial solidification behavior in a bloom mold loaded with EMS were investigated. The aim is to propose a better SEN condition for the big bloom casting of high railway steel. The water simulation experiments were conducted to show the flow characteristics under different SEN conditions and verify the numerical model of flow pattern. The experimental and numerical simulation results showed that the optimized four-port SEN with diagonal installation cannot only improve the flow pattern of the molten steel by alleviating the level fluctuation and reducing the impact pressure to the wall. It is also beneficial for temperature variation at both bloom surface and corner, as well as the local solidified shell thinning phenomena due to the elimination of impingement effect. Full article
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Open AccessArticle Kohonen Neural Network Classification for Failure Process of Metallic Organic Coating in Corrosion Environment
Metals 2017, 7(4), 147; doi:10.3390/met7040147
Received: 21 December 2016 / Revised: 29 March 2017 / Accepted: 14 April 2017 / Published: 20 April 2017
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Abstract
A deeper insight into the changing states of corrosion during certain exposure circumstances has been investigated by applying Kohonen networks. The Kohonen network has been trained by four sets of samples and tested using another sample. All the sample data were collected during
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A deeper insight into the changing states of corrosion during certain exposure circumstances has been investigated by applying Kohonen networks. The Kohonen network has been trained by four sets of samples and tested using another sample. All the sample data were collected during accelerated corrosion experiments and the network took the changing rate of impedance of each cycle as an input. Compared with traditional classification, the Kohonen artificial network method classifies corrosion process into five sub-processes which is a refinement of three typical corrosion processes. The two newly defined sub-processes of corrosion—namely, pre-middle stage and post-middle stage—were introduced. The EIS data and macro-morphology for both sub-processes were analyzed through accelerated experiments. The classification results of the Kohonen artificial network are highly consistent with the predictions based on impedance magnitude at low frequency, which illustrates that the Kohonen network classification is an effective method for predicting the failure cycles of polymer coatings. Full article
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Open AccessArticle Formation and Corrosion Behavior of Mechanically-Alloyed Cu–Zr–Ti Bulk Metallic Glasses
Metals 2017, 7(4), 148; doi:10.3390/met7040148
Received: 31 August 2016 / Revised: 8 April 2017 / Accepted: 18 April 2017 / Published: 20 April 2017
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Abstract
Cu60Zr30Ti10 metallic glass powder was prepared by mechanically alloying a mixture of pure Cu, Zr, and Ti powders after 5 h of milling. Cu60Zr30Ti10 bulk metallic glass (BMG) was synthesized by vacuum hot
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Cu60Zr30Ti10 metallic glass powder was prepared by mechanically alloying a mixture of pure Cu, Zr, and Ti powders after 5 h of milling. Cu60Zr30Ti10 bulk metallic glass (BMG) was synthesized by vacuum hot pressing the as-milled Cu60Zr30Ti10 metallic glass powder at 746 K in the pressure range of 0.72–1.20 GPa, and the structure was analyzed through X-ray diffraction and transmission electron microscopy. The pressure could enhance the thermal stability, and prolong the existence, of the amorphous phase inside the Cu60Zr30Ti10 powder. Furthermore, the corrosion behavior of the Cu-based BMG in four corrosive media was studied using a potentiodynamic method. The Cu60Zr30Ti10 BMG exhibited a low corrosion rate and current density in 1 N solutions of H2SO4, NaOH, and HNO3. X-ray photoelectron spectroscopy results revealed that the formation of Zr- and Ti-rich passive oxide layers provides a high corrosion resistance against 1 N H2SO4 and HNO3 solutions, and the breakdown of the protective film by Cl attack was responsible for pitting corrosion in a 3 wt % NaCl solution. The formation of oxide films and the nucleation and growth of pitting were analyzed through microstructural investigations. Full article
(This article belongs to the Special Issue Mechanical Alloying)
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Open AccessArticle Effect of Parameters on Internal Crack Healing in 30Cr2Ni4MoV Steel for 600-Ton Ultra-Super Ingots
Metals 2017, 7(4), 149; doi:10.3390/met7040149
Received: 21 March 2017 / Revised: 15 April 2017 / Accepted: 19 April 2017 / Published: 21 April 2017
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Abstract
The effect of parameters on internal crack healing in 30Cr2Ni4MoV steel for 600-ton ultra-super ingots was systematically investigated. The results show that the degree of crack healing increases with increasing healing temperature, holding time, reduction ratio, and hot pressure, and with decreasing strain
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The effect of parameters on internal crack healing in 30Cr2Ni4MoV steel for 600-ton ultra-super ingots was systematically investigated. The results show that the degree of crack healing increases with increasing healing temperature, holding time, reduction ratio, and hot pressure, and with decreasing strain rate. Internal crack healing in 30Cr2Ni4MoV steel should be conducted at less than 1200 °C to avoid grain coarsening. Hot pressure, in the high-temperature elastic zone and perpendicular to the crack faces, not only promotes the rapid crack healing, but also prevents grain coarsening of the matrix. Full article
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Open AccessArticle Microstructure and Mechanical Properties of J55ERW Steel Pipe Processed by On-Line Spray Water Cooling
Metals 2017, 7(4), 150; doi:10.3390/met7040150
Received: 17 August 2016 / Revised: 19 March 2017 / Accepted: 4 April 2017 / Published: 23 April 2017
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Abstract
An on-line spray water cooling (OSWC) process for manufacturing electric resistance welded (ERW) steel pipes is presented to enhance their mechanical properties and performances. This technique reduces the processing needed for the ERW pipe and overcomes the weakness of the conventional manufacturing technique.
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An on-line spray water cooling (OSWC) process for manufacturing electric resistance welded (ERW) steel pipes is presented to enhance their mechanical properties and performances. This technique reduces the processing needed for the ERW pipe and overcomes the weakness of the conventional manufacturing technique. Industrial tests for J55 ERW steel pipe were carried out to validate the effectiveness of the OSWC process. The microstructure and mechanical properties of the J55 ERW steel pipe processed by the OSWC technology were investigated. The optimized OSWC technical parameters are presented based on the mechanical properties and impact the performance of steel pipes. The industrial tests show that the OSWC process can be used to efficiently control the microstructure, enhance mechanical properties, and improve production flexibility of steel pipes. The comprehensive mechanical properties of steel pipes processed by the OSWC are superior to those of other published J55 grade steels. Full article
(This article belongs to the Special Issue Process-Structure-Property Relationships in Metals)
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Open AccessArticle Reduced Fracture Toughness of Metallic Glass at Cryogenic Temperature
Metals 2017, 7(4), 151; doi:10.3390/met7040151
Received: 27 February 2017 / Revised: 16 April 2017 / Accepted: 18 April 2017 / Published: 23 April 2017
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Abstract
The effects of cryogenic temperature on the toughness of a Zr-based metallic glass are investigated. Based on three-dimensional fracture morphologies at different temperatures, the crack formation and propagation are analyzed. Through the calculation of the shear transformation zone volume, the shear modulus and
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The effects of cryogenic temperature on the toughness of a Zr-based metallic glass are investigated. Based on three-dimensional fracture morphologies at different temperatures, the crack formation and propagation are analyzed. Through the calculation of the shear transformation zone volume, the shear modulus and bulk modulus of the metallic glass at different temperatures and the crack formation mechanism associated with the temperature is discussed. Once the crack commences propagation, the hyperelasticity model is used to elucidate the fractographic evolution of crack propagation. Full article
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