Metals

8741 KiB

Open AccessArticle

The Microstructures and Tensile Properties of As-Extruded Mg–4Sm–xZn–0.5Zr (x = 0, 1, 2, 3, 4 wt %) Alloys

by Chaojie Che, Zhongyi Cai, Liren Cheng, Fanxing Meng and Zhen Yang

Metals 2017, 7(7), 281; https://doi.org/10.3390/met7070281 - 24 Jul 2017

Cited by 9 | Viewed by 4331

The microstructures and tensile properties of as-cast and as-extruded Mg–4Sm–xZn–0.5Zr (x = 0, 1, 2, 3, 4 wt %) alloys were systematically investigated by optical microscope, X-ray diffractometer (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM). Numerous nanoscale [...] Read more.

The microstructures and tensile properties of as-cast and as-extruded Mg–4Sm–xZn–0.5Zr (x = 0, 1, 2, 3, 4 wt %) alloys were systematically investigated by optical microscope, X-ray diffractometer (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM). Numerous nanoscale dynamic precipitates could be observed in the as-extruded alloys containing high content of Zn, and the nanoscale particles were termed as (Mg,Zn)₃Sm phase. Some basal disc-like precipitates were observed in as-extruded Mg–4Sm–4Zn–0.5Zr alloy, which were proposed to have a hexagonal structure with a = 0.556 nm. The dynamic precipitates effectively pinned the motions of DRXed (dynamic recrystallized) grain boundaries leading to an obvious reduction of DRXed grain size, and the tensile yield strength of as-extruded alloy was improved. The as-extruded Mg–4Sm–4Zn–0.5Zr alloy exhibits the best comprehensive mechanical properties at room temperature among all the alloys, and the yield strength, ultimate tensile strength and elongation are about 246 MPa, 273 MPa and 21% respectively. Full article

(This article belongs to the Special Issue Microstructure and Mechanical Properties of Structural Metals and Alloys)

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4426 KiB

Open AccessArticle

Effect of Structural Heterogeneity of 17Mn1Si Steel on the Temperature Dependence of Impact Deformation and Fracture

by Dmitry Moiseenko, Pavlo Maruschak, Sergey Panin, Pavel Maksimov, Ilya Vlasov, Filippo Berto, Siegfried Schmauder and Alexey Vinogradov

Metals 2017, 7(7), 280; https://doi.org/10.3390/met7070280 - 22 Jul 2017

Cited by 4 | Viewed by 5054

Abstract

The paper deals with a theoretical and experimental study of the relationship between the microstructural parameters, mechanical properties, and impact deformation and fracture of steels using the example of 17Mn1Si pipe steel. A model for the behavior of a polycrystalline grain conglomerate under [...] Read more.

The paper deals with a theoretical and experimental study of the relationship between the microstructural parameters, mechanical properties, and impact deformation and fracture of steels using the example of 17Mn1Si pipe steel. A model for the behavior of a polycrystalline grain conglomerate under impact loading at different temperatures was proposed within a cellular automata framework. It was shown that the intensity of dissipation processes explicitly depends on temperature and these processes play an important role in stress relaxation at the boundaries of structural elements. The Experimental study reveals the relationship between pendulum impact test temperature and the deformation/fracture energy of the steel. The impact toughness was shown to decrease almost linearly with the decreasing test temperature, which agrees with the fractographic analysis data confirming the increase in the fraction of brittle fracture in this case. It was shown with the aid of the proposed model and numerical simulations that the use of the excitable cellular automata method and an explicit account of test temperature through the possibility of energy release at internal interfaces help to explain the experimentally observed features of impact failure at different temperatures. Full article

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4505 KiB

Open AccessArticle

Aluminum and Nickel Matrix Composites Reinforced by CNTs: Dispersion/Mixture by Ultrasonication

by Sónia Simões, Filomena Viana, Marcos A. L. Reis and Manuel F. Vieira

Metals 2017, 7(7), 279; https://doi.org/10.3390/met7070279 - 22 Jul 2017

Cited by 55 | Viewed by 8042

Abstract

The main challenge in the production of metal matrix composites reinforced by carbon nanotubes (CNTs) is the development of a manufacturing process ensuring the dispersion of nanoparticles without damaging them, and the formation of a strong bond with the metallic matrix to achieve [...] Read more.

The main challenge in the production of metal matrix composites reinforced by carbon nanotubes (CNTs) is the development of a manufacturing process ensuring the dispersion of nanoparticles without damaging them, and the formation of a strong bond with the metallic matrix to achieve an effective load transfer, so that the maximum reinforcement effect of CNTs will be accomplished. This research focuses on the production by powder metallurgy of aluminum and nickel matrix composites reinforced by CNTs, using ultrasonication as the dispersion and mixture process. Microstructural characterization of nanocomposites was performed by optical microscopy (OM), scanning and transmission electron microscopy (SEM and TEM), electron backscattered diffraction (EBSD) and high-resolution transmission electron microscopy (HRTEM). Microstructural characterization revealed that the use of ultrasonication as the dispersion and mixture process in the production of Al/CNT and Ni/CNT nanocomposites promoted the dispersion and embedding of individual CNT in the metallic matrices. CNT clusters at grain boundary junctions were also observed. The strengthening effect of the CNTs is shown by the increase in hardness for all nanocomposites. The highest hardness values were observed for Al/CNT and Ni/CNT nanocomposites, with a 1.00 vol % CNTs. Full article

(This article belongs to the Special Issue Metal Matrix Composites)

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4904 KiB

Open AccessArticle

Effect of Pyrite on Thiosulfate Leaching of Gold and the Role of Ammonium Alcohol Polyvinyl Phosphate (AAPP)

by Xiaoliang Liu, Bin Xu, Xin Min, Qian Li, Yongbin Yang, Tao Jiang, Yinghe He and Xi Zhang

Metals 2017, 7(7), 278; https://doi.org/10.3390/met7070278 - 19 Jul 2017

Cited by 29 | Viewed by 6072

Abstract

The effect of pyrite and the role of ammonium alcohol polyvinyl phosphate (AAPP) during gold leaching in ammoniacal thiosulfate solutions were investigated using pure gold foils. The results showed that pyrite catalyzed the decomposition and also significantly increased the consumption of thiosulfate. This [...] Read more.

The effect of pyrite and the role of ammonium alcohol polyvinyl phosphate (AAPP) during gold leaching in ammoniacal thiosulfate solutions were investigated using pure gold foils. The results showed that pyrite catalyzed the decomposition and also significantly increased the consumption of thiosulfate. This detrimental effect became more severe with increasing pyrite content. Further, the presence of pyrite also substantially slowed the gold leaching kinetics and reduced the overall gold dissolution. The reduction in gold dissolution was found to be caused primarily by the surface passivation of the gold. The negative effects of pyrite, however, can be alleviated by the addition of AAPP. Comparison of zeta potentials of pyrite with and without AAPP suggests that AAPP had adsorbed on the surface of the pyrite and weakened the catalytic effect of pyrite on the thiosulfate decomposition by blocking the contact between the pyrite and thiosulfate anions. AAPP also competed with thiosulfate anions to complex with the cupric ion at the axial coordinate sites, and thus abated the oxidation of thiosulfate by cupric ions. Moreover, the indiscriminate adsorption of AAPP on the surfaces of gold and passivation species prevented the passivation of the gold surface by surface charge and electrostatic repulsion. Therefore, AAPP effectively stabilized the thiosulfate in the solution and facilitated the gold leaching in the presence of pyrite. Full article

(This article belongs to the Special Issue Valuable Metal Recycling)

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886 KiB

Open AccessArticle

Transition of the Interface between Iron and Carbide Precipitate From Coherent to Semi-Coherent

by Hideaki Sawada, Shunsuke Taniguchi, Kazuto Kawakami and Taisuke Ozaki

Metals 2017, 7(7), 277; https://doi.org/10.3390/met7070277 - 19 Jul 2017

Cited by 22 | Viewed by 6410

Abstract

There are some precipitates that undergo transition from a coherent to semi-coherent state during growth. An example of such a precipitate in steel is carbide with a NaCl-type structure, such as TiC and NbC. The interface energy between carbide precipitate and iron is [...] Read more.

There are some precipitates that undergo transition from a coherent to semi-coherent state during growth. An example of such a precipitate in steel is carbide with a NaCl-type structure, such as TiC and NbC. The interface energy between carbide precipitate and iron is obtained via large-scale first-principles electronic structure calculation. The strain energy is estimated by structure optimization of the iron matrix with virtual carbide precipitate using the empirical potential. The transition of the interface from a coherent to semi-coherent state was examined by comparing the interface and strain energies between the coherent and semi-coherent interfaces. The sizes where both the precipitates undergo this transition are smaller than those of the interfaces with minimum misfit. The estimated transition diameter of TiC is in agreement with the experimentally obtained value. Full article

(This article belongs to the Special Issue First-Principles Approaches to Metals, Alloys, and Metallic Compounds)

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3184 KiB

Open AccessArticle

by Ren-Kae Shiue, Shyi-Kaan Wu, Sheng-Hao Yang and Chun-Kai Liu

Metals 2017, 7(7), 276; https://doi.org/10.3390/met7070276 - 18 Jul 2017

Cited by 4 | Viewed by 4500

Abstract

Infrared dissimilar joining Ti₅₀Ni₅₀ and 316L stainless steel using Cu foil in between Cusil-ABA and BAg-8 filler metals has been studied. The Cu foil serves as a barrier layer with thicknesses of 70 μm and 50 μm, and it successfully [...] Read more.

Infrared dissimilar joining Ti₅₀Ni₅₀ and 316L stainless steel using Cu foil in between Cusil-ABA and BAg-8 filler metals has been studied. The Cu foil serves as a barrier layer with thicknesses of 70 μm and 50 μm, and it successfully isolates the interfacial reaction between Ti and Fe at the 316L SS (stainless steel) substrate side. In contrast, the Cu foil with 25 μm in thickness is completely dissolved into the braze melt during brazing and fails to be a barrier layer. A layer of (Cu_xNi_1−x)₂Ti intermetallic is formed at the Ti₅₀Ni₅₀ substrate side, and the Cu interlayer is dissolved into the Cusil-ABA melt to from a few proeutectic Cu particles for all specimens. For the 316L SS substrate side, no interfacial layer is observed and (Ag, Cu) eutectic dominates the brazed joint for 70 μm/50 μm Cu foil. The average shear strength of the bond with Cu barrier layer is greatly increased compared with that without Cu. The brazed joints with a 50 μm Cu layer demonstrate the highest average shear strengths of 354 MPa and 349 MPa for samples joined at 820 °C and 850 °C, respectively. Cracks are initiated/propagated in (Ag, Cu) eutectic next to the 316L substrate side featured with ductile dimple fracture. It shows great potential for industrial application. Full article

(This article belongs to the Special Issue Shape Memory Alloys 2017)

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11151 KiB

Open AccessArticle

Feature Size Effect on Formability of Multilayer Metal Composite Sheets under Microscale Laser Flexible Forming

by Huixia Liu, Wenhao Zhang, Jenn-Terng Gau, Zongbao Shen, Youjuan Ma, Guoce Zhang and Xiao Wang

Metals 2017, 7(7), 275; https://doi.org/10.3390/met7070275 - 18 Jul 2017

Cited by 14 | Viewed by 4401

Abstract

Multilayer metal composite sheets possess superior properties to monolithic metal sheets, and formability is different from monolithic metal sheets. In this research, the feature size effect on formability of multilayer metal composite sheets under microscale laser flexible forming was studied by experiment. Two-layer [...] Read more.

Multilayer metal composite sheets possess superior properties to monolithic metal sheets, and formability is different from monolithic metal sheets. In this research, the feature size effect on formability of multilayer metal composite sheets under microscale laser flexible forming was studied by experiment. Two-layer copper/nickel composite sheets were selected as experimental materials. Five types of micro molds with different diameters were utilized. The formability of materials was evaluated by forming depth, thickness thinning, surface quality, and micro-hardness distribution. The research results showed that the formability of two-layer copper/nickel composite sheets was strongly influenced by feature size. With feature size increasing, the effect of layer stacking sequence on forming depth, thickness thinning ratio, and surface roughness became increasingly larger. However, the normalized forming depth, thickness thinning ratio, surface roughness, and micro-hardness of the formed components under the same layer stacking sequence first increased and then decreased with increasing feature size. The deformation behavior of copper/nickel composite sheets was determined by the external layer. The deformation extent was larger when the copper layer was set as the external layer. Full article

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20548 KiB

Open AccessArticle

Investigation of Service Life Prediction Models for Metallic Organic Coatings Using Full-Range Frequency EIS Data

by Yuanming Xu, Junshuang Ran, Wei Dai and Weifang Zhang

Metals 2017, 7(7), 274; https://doi.org/10.3390/met7070274 - 17 Jul 2017

Cited by 15 | Viewed by 4151

Abstract

Various service life prediction models of organic coatings were analyzed based on the acquirement of the measurement of Electrochemical Impedance Spectroscopy (EIS) from indoor accelerated tests. First, some theoretical formulas on corrosion lifetime predictions of coatings were introduced, followed by the comparative assessment [...] Read more.

Various service life prediction models of organic coatings were analyzed based on the acquirement of the measurement of Electrochemical Impedance Spectroscopy (EIS) from indoor accelerated tests. First, some theoretical formulas on corrosion lifetime predictions of coatings were introduced, followed by the comparative assessment of four practical prediction models in view of prediction accuracy in application. The prediction from impedance data at single low frequency |Z| _{0.1 Hz}, the classical degradation kinetics, and proposed improved degradation kinetics model, as well as a self-organized neural network prediction based on sample detection, were focused in this paper. The standard AF1410 plates employed as the metallic substrates were coated with sprayed zinc layer, epoxy-ester primer and polyurethane enamel layer. The accelerated experiments which mimicked coastal areas of China were carried out with the specimens after surface treatment. The assessment of results showed that the proposed improved degradation kinetics model and neural network classification model based on the full range of frequency data obviously have higher prediction accuracies than the traditional degradation kinetics model, and the prediction precision of the sample detection-based neural network classification was the highest among these models. The study gives some insights for coating degradation lifetime prediction which may be useful and supportive for practical applications. Full article

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3951 KiB

Open AccessArticle

Excellent Performance of Fe₇₈Si₉B₁₃ Metallic Glass for Activating Peroxymonosulfate in Degradation of Naphthol Green B

by Xue-Fen Li, Shun-Xing Liang, Xiao-Wang Xi, Zhe Jia, Shi-Kun Xie, He-Chun Lin, Jun-Ping Hu and Lai-Chang Zhang

Metals 2017, 7(7), 273; https://doi.org/10.3390/met7070273 - 17 Jul 2017

Cited by 31 | Viewed by 5565

Abstract

The functional application of metallic glasses in the catalytic field has widely attracted research attention due to its unique atomic structure compared to crystalline materials. It has been reported that metallic glasses can effectively activate H₂O₂ and persulfate, yet the [...] Read more.

The functional application of metallic glasses in the catalytic field has widely attracted research attention due to its unique atomic structure compared to crystalline materials. It has been reported that metallic glasses can effectively activate H₂O₂ and persulfate, yet the activation of peroxymonosulfate by metallic glasses is not studied well. In this work, the metallic glass with atomic composition of Fe₇₈Si₉B₁₃ was applied for investigating the peroxymonosulfate (PMS) activation on degradation of naphthol green B (NGB) dye. The change of surface morphology indicated the important role of oxide films during the dye degradation. The effects and first-order kinetics model of various reaction parameters were evaluated systematically, including PMS concentration, catalyst dosage, irradiation intensity, and dye concentration. The results showed that about 98% of the dye removal rate could be achieved only within 10 min under rational conditions. The reaction kinetics k of 0.1339 min⁻¹ without ribbons was sharply improved to 0.3140 min⁻¹ by adding 0.5 g/L ribbons, indicating the superior activation ability of Fe₇₈Si₉B₁₃ metallic glass. The recycling experiment revealed that the Fe₇₈Si₉B₁₃ ribbons exhibited the excellent surface stability and catalytic reusability for activating PMS even after reused for 10th run. Full article

(This article belongs to the Special Issue Bulk Metallic Glasses)

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4646 KiB

Open AccessArticle

An Efficient Approach for Lithium and Aluminum Recovery from Coal Fly Ash by Pre-Desilication and Intensified Acid Leaching Processes

by Shenyong Li, Shenjun Qin, Lianwei Kang, Jianjun Liu, Jing Wang and Yanheng Li

Metals 2017, 7(7), 272; https://doi.org/10.3390/met7070272 - 14 Jul 2017

Cited by 42 | Viewed by 8090

Abstract

A novel technique was developed for the recovery of lithium and aluminum from coal fly ash using a combination of pre-desilication and an intensified acid leaching process. The main components of the high-aluminum fly ash were found to be Al₂O₃ [...] Read more.

A novel technique was developed for the recovery of lithium and aluminum from coal fly ash using a combination of pre-desilication and an intensified acid leaching process. The main components of the high-aluminum fly ash were found to be Al₂O₃ and SiO₂, and the Al/Si ratio increased from 1.0 to 1.5 after desiliconization. The lithium content of the coal fly ash met national recycling standards. The optimal acid leaching conditions, under which the leaching efficiencies of lithium and aluminum were 82.23% and 76.72%, respectively, were as follows: 6 mol/L HCl, 1:20 solid to liquid ratio, 120 °C and 4 h. During the hydrochloric acid pressure leaching process, spherical particles of desilicated fly ash were decomposed into flakes. Part of the mullite phase was dissolved, and most of the glass phase leached into the liquor. The generation of the silicates hindered lithium transport, which decreased the leaching rate of lithium. This work suggests that the preprocessing is a promising option for effective recovery of high-aluminum and fly ash-associated lithium. Full article

(This article belongs to the Special Issue Valuable Metal Recycling)

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5234 KiB

Open AccessArticle

In-Situ Investigation of Strain-Induced Martensitic Transformation Kinetics in an Austenitic Stainless Steel by Inductive Measurements

by Carola Celada-Casero, Harm Kooiker, Manso Groen, Jan Post and David San-Martin

Metals 2017, 7(7), 271; https://doi.org/10.3390/met7070271 - 13 Jul 2017

Cited by 36 | Viewed by 7182

Abstract

An inductive sensor developed by Philips ATC has been used to study in-situ the austenite (γ) to martensite (α′) phase transformation kinetics during tensile testing in an AISI 301 austenitic stainless steel. A correlation between the sensor output signal and the volume fraction [...] Read more.

An inductive sensor developed by Philips ATC has been used to study in-situ the austenite (γ) to martensite (α′) phase transformation kinetics during tensile testing in an AISI 301 austenitic stainless steel. A correlation between the sensor output signal and the volume fraction of α′-martensite has been found by comparing the results to the ex-situ characterization by magnetization measurements, light optical microscopy, and X-ray diffraction. The sensor has allowed for the observation of the stepwise transformation behavior, a not-well-understood phenomena that takes place in large regions of the bulk material and that so far had only been observed by synchrotron X-ray diffraction. Full article

(This article belongs to the Special Issue Bainite and Martensite: Developments and Challenges)

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19818 KiB

Open AccessArticle

Effects of Welding Speed on Microstructure and Mechanical Property of Fiber Laser Welded Dissimilar Butt Joints between AISI316L and EH36

by Longchao Cao, Xinyu Shao, Ping Jiang, Qi Zhou, Youmin Rong, Shaoning Geng and Gaoyang Mi

Metals 2017, 7(7), 270; https://doi.org/10.3390/met7070270 - 13 Jul 2017

Cited by 19 | Viewed by 6170

Abstract

Fiber laser welding of dissimilar materials between AISI316L austenitic stainless steel and EH36 ship steels were conducted. Then the effects of welding speed on microstructure and mechanical characterization of the welded joint were investigated. Optical microscopy, Scanning Electron Microscopy (SEM), and X-ray Diffraction [...] Read more.

Fiber laser welding of dissimilar materials between AISI316L austenitic stainless steel and EH36 ship steels were conducted. Then the effects of welding speed on microstructure and mechanical characterization of the welded joint were investigated. Optical microscopy, Scanning Electron Microscopy (SEM), and X-ray Diffraction (XRD) were used to analyze the microstructure. Microhardness testing, transverse tensile strength, and impact tests at the temperature of −40 °C were performed to study the mechanical properties. The martensite phase formed due to the rapid cooling rate during laser welding and low Cr_eq/Ni_eq ratio. The coarse martensite grains in the center seam are transformed to finer martensite grains as the welding speed increases resulting in the higher cooling rate. The microhardness of joints was about 350 HV_0.3, which was twice that of the base metal because of the formation of the martensite phase. When the welding speed was 0.6 m/min, fewer defects were found, and tensile testing indicated overmatching of the weld metal relative to the base metal. In addition, the joints also exhibited better ductility and impact toughness. Full article

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11583 KiB

Open AccessFeature PaperArticle

Microstructure and Mechanical Properties of Ti5553 Butt Welds Performed by LBW under Conduction Regime

by Jose Maria Sánchez-Amaya, Timotius Pasang, Margarita Raquel Amaya-Vazquez, Juan De Dios Lopez-Castro, Cristina Churiaque, Yuan Tao and Francisco Javier Botana Pedemonte

Metals 2017, 7(7), 269; https://doi.org/10.3390/met7070269 - 13 Jul 2017

Cited by 15 | Viewed by 8291

Abstract

Ti-5Al-5V-5Mo-3Cr (Ti5553) is a metastable β titanium alloy with a high potential use in the aeronautic industry due to its high strength, excellent hardenability, fracture toughness and high fatigue resistance. However, recent research shows this alloy has a limited weldability. Different welding technologies [...] Read more.

Ti-5Al-5V-5Mo-3Cr (Ti5553) is a metastable β titanium alloy with a high potential use in the aeronautic industry due to its high strength, excellent hardenability, fracture toughness and high fatigue resistance. However, recent research shows this alloy has a limited weldability. Different welding technologies have been applied in the literature to weld this alloy, such as electron beam welding (EBW), gas tungsten arc welding (GTAW) or laser beam welding (LBW) under keyhole regime. Thus, in tensile tests, joints normally break at the weld zones, the strength of the welds being always lower than that of the base metal. In the present work, a novel approach, based on the application of LBW under conduction regime (with a High-Power Diode Laser, HPDL), has been employed for the first time to weld this alloy. Microstructure, microhardness and strength of obtained welds were analyzed and reported in this paper. LBW under conduction regime (LBW-CR) leads to welds with slightly higher values of Ultimate Tensile Strength (UTS) than those previously obtained with other joining processes, probably due to the higher hardness of the fusion zone and to lower porosity of the weld. Full article

(This article belongs to the Special Issue Laser Welding)

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7467 KiB

Open AccessArticle

Investigation on Deformation Mechanisms of NiTi Shape Memory Alloy Tube under Radial Loading

by Shuyong Jiang, Junbo Yu, Li Hu and Yanqiu Zhang

Metals 2017, 7(7), 268; https://doi.org/10.3390/met7070268 - 13 Jul 2017

Cited by 7 | Viewed by 8237

Abstract

NiTi shape memory alloy (SMA) tube was coupled with mild steel cylinder in order to investigate deformation mechanisms of NiTi SMA tubes undergoing radial loading. NiTi SMA tubes of interest deal with two kinds of nominal compositions; namely, Ni-50 at % Ti and [...] Read more.

NiTi shape memory alloy (SMA) tube was coupled with mild steel cylinder in order to investigate deformation mechanisms of NiTi SMA tubes undergoing radial loading. NiTi SMA tubes of interest deal with two kinds of nominal compositions; namely, Ni-50 at % Ti and Ni-49.1 at % Ti, where at room temperature, B19′ martensite is dominant in the former, and B2 austensite is complete in the latter. The mechanics of the NiTi SMA tube during radial loading were analyzed based on elastic mechanics and plastic yield theory, where effective stress and effective strain are determined as two important variables that investigate deformation mechanisms of the NiTi SMA tube during radial loading. As for the NiTi SMA tube with austenite structure, stress-induced martensite (SIM) transformation as well as plastic deformation of SIM occur with the continuous increase of effective stress. As for NiTi SMA tube which possesses martensite structure, reorientation and detwinning of twinned martensite as well as plastic deformation of reoriented and detwinned martensite occur with the continuous increase in the effective stress. Plastic deformation for dislocation slip has a negative impact on superelasticity and shape memory effect of NiTi SMA tube. Full article

(This article belongs to the Special Issue Shape Memory Alloys 2017)

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17766 KiB

Open AccessArticle

Microstructure and Mechanical Properties of Ti6Al4V Alloy Modified and Reinforced by In Situ Ti₅Si₃/Ti Composite Ribbon Inoculants

by Nuo Li, Chunxiang Cui, Shuangjin Liu, Shuiqing Liu, Sen Cui and Qian Wang

Metals 2017, 7(7), 267; https://doi.org/10.3390/met7070267 - 12 Jul 2017

Cited by 18 | Viewed by 8350

Abstract

This paper deals with a novel fabrication method (a vacuum rapid solidification technique) to prepare in situ Ti₅Si₃/Ti composite ribbon as inoculants to modify Ti6Al4V alloy to obtain titanium matrix composites (TMCs). Microstructure and morphology observations showed that the [...] Read more.

This paper deals with a novel fabrication method (a vacuum rapid solidification technique) to prepare in situ Ti₅Si₃/Ti composite ribbon as inoculants to modify Ti6Al4V alloy to obtain titanium matrix composites (TMCs). Microstructure and morphology observations showed that the grain size of the TMCs was refined as the volume fraction of inoculants increased. The grain size of the TMCs can be refined from a grade of 650 μm to about 110 μm with a very small refiner adding ratio of 0.6% in weight. Thereafter, the mechanical properties of the TMCs, including their tensile strength, microhardness, impact properties, and resistant properties were improved obviously by adding the ribbon inoculants. The excellent grain refining and reinforcement effect can be attributed to the nano-sized Ti₅Si₃ refiner particles distributed homogeneously in the matrix, the well-banded particle/matrix interface, and the good wettability between the Ti₅Si₃ particles in inoculants and the Ti6Al4V alloy melt, which are benefit for the heterogeneous nucleation of the TMCs during solidification. Full article

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186 KiB

Open AccessEditorial

Metals Challenged by Neutron and Synchrotron Radiation

by Klaus-Dieter Liss

Metals 2017, 7(7), 266; https://doi.org/10.3390/met7070266 - 11 Jul 2017

Cited by 13 | Viewed by 4360

Abstract

In the past one and a half decades, neutron and synchrotron radiation techniques have come to the forefront as an excellent set of tools for the wider investigation of material structures and properties [1,2], becoming available to a large user community.[...] Full article

(This article belongs to the Special Issue Metals Challenged by Neutron and Synchrotron Radiation)

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4010 KiB

Open AccessArticle

Low Cycle Fatigue Behaviour of DP Steels: Micromechanical Modelling vs. Validation

by Ghazal Moeini, Ali Ramazani, Sebastian Myslicki, Veera Sundararaghavan and Carsten Könke

Metals 2017, 7(7), 265; https://doi.org/10.3390/met7070265 - 11 Jul 2017

Cited by 10 | Viewed by 6725

Abstract

This study aims to simulate the stabilised stress-strain hysteresis loop of dual phase (DP) steel using micromechanical modelling. For this purpose, the investigation was conducted both experimentally and numerically. In the experimental part, the microstructure characterisation, monotonic tensile tests and low cycle fatigue [...] Read more.

This study aims to simulate the stabilised stress-strain hysteresis loop of dual phase (DP) steel using micromechanical modelling. For this purpose, the investigation was conducted both experimentally and numerically. In the experimental part, the microstructure characterisation, monotonic tensile tests and low cycle fatigue tests were performed. In the numerical part, the representative volume element (RVE) was employed to study the effect of the DP steel microstructure of the low cycle fatigue behavior of DP steel. A dislocation-density based model was utilised to identify the tensile behavior of ferrite and martensite. Then, by establishing a correlation between the monotonic and cyclic behavior of ferrite and martensite phases, the cyclic deformation properties of single phases were estimated. Accordingly, Chaboche kinematic hardening parameters were identified from the predicted cyclic curve of individual phases in DP steel. Finally, the predicted hysteresis loop from low cycle fatigue modelling was in very good agreement with the experimental one. The stabilised hysteresis loop of DP steel can be successfully predicted using the developed approach. Full article

(This article belongs to the Special Issue Microstructure based Modeling of Metallic Materials)

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3409 KiB

Open AccessFeature PaperArticle

The Role of κ-Carbides as Hydrogen Traps in High-Mn Steels

by Tobias A. Timmerscheidt, Poulumi Dey, Dimitri Bogdanovski, Jörg Von Appen, Tilmann Hickel, Jörg Neugebauer and Richard Dronskowski

Metals 2017, 7(7), 264; https://doi.org/10.3390/met7070264 - 11 Jul 2017

Cited by 35 | Viewed by 7204

Abstract

Since the addition of Al to high-Mn steels is known to reduce their sensitivity to hydrogen-induced delayed fracture, we investigate possible trapping effects connected to the presence of Al in the grain interior employing density-functional theory (DFT). The role of Al-based precipitates is [...] Read more.

Since the addition of Al to high-Mn steels is known to reduce their sensitivity to hydrogen-induced delayed fracture, we investigate possible trapping effects connected to the presence of Al in the grain interior employing density-functional theory (DFT). The role of Al-based precipitates is also investigated to understand the relevance of short-range ordering effects. So-called E2₁-Fe₃AlC κ-carbides are frequently observed in Fe-Mn-Al-C alloys. Since H tends to occupy the same positions as C in these precipitates, the interaction and competition between both interstitials is also investigated via DFT-based simulations. While the individual H–H/C–H chemical interactions are generally repulsive, the tendency of interstitials to increase the lattice parameter can yield a net increase of the trapping capability. An increased Mn content is shown to enhance H trapping due to attractive short-range interactions. Favorable short-range ordering is expected to occur at the interface between an Fe matrix and the E2₁-Fe₃AlC κ-carbides, which is identified as a particularly attractive trapping site for H. At the same time, accumulation of H at sites of this type is observed to yield decohesion of this interface, thereby promoting fracture formation. The interplay of these effects, evident in the trapping energies at various locations and dependent on the H concentration, can be expressed mathematically, resulting in a term that describes the hydrogen embrittlement. Full article

(This article belongs to the Special Issue First-Principles Approaches to Metals, Alloys, and Metallic Compounds)

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7843 KiB

Open AccessArticle

Bainitic Transformation and Properties of Low Carbon Carbide-Free Bainitic Steels with Cr Addition

by Mingxing Zhou, Guang Xu, Junyu Tian, Haijiang Hu and Qing Yuan

Metals 2017, 7(7), 263; https://doi.org/10.3390/met7070263 - 10 Jul 2017

Cited by 37 | Viewed by 8087

Abstract

Two low carbon carbide-free bainitic steels (with and without Cr addition) were designed, and each steel was treated by two kinds of heat treatment procedure (austempering and continuous cooling). The effects of Cr addition on bainitic transformation, microstructure, and properties of low carbon [...] Read more.

Two low carbon carbide-free bainitic steels (with and without Cr addition) were designed, and each steel was treated by two kinds of heat treatment procedure (austempering and continuous cooling). The effects of Cr addition on bainitic transformation, microstructure, and properties of low carbon bainitic steels were investigated by dilatometry, metallography, X-ray diffraction, and a tensile test. The results show that Cr addition hinders the isothermal bainitic transformation, and this effect is more significant at higher transformation temperatures. In addition, Cr addition increases the tensile strength and elongation simultaneously for austempering treatment at a lower temperature. However, when the austempering temperature is higher, the strength increases and the elongation obviously decreases by Cr addition, resulting in the decrease in the product of tensile strength and elongation. Meanwhile, the austempering temperature should be lower in Cr-added steel than that in Cr-free steel in order to obtain better comprehensive properties. Moreover, for the continuous cooling treatment in the present study, the product of tensile strength and elongation significantly decreases with Cr addition due to more amounts of martensite. Full article

(This article belongs to the Special Issue Alloy Steels)

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4836 KiB

Open AccessArticle

Effect of Fe-Content on the Mechanical Properties of Recycled Al Alloys during Hot Compression

by Hongzhou Lu, Zeran Hou, Mingtu Ma and Guimin Lu

Metals 2017, 7(7), 262; https://doi.org/10.3390/met7070262 - 10 Jul 2017

Cited by 14 | Viewed by 4443

Abstract

It is unavoidable that Fe impurities will be mixed into Al alloys during recycling of automotive aluminum parts, and the Fe content has a significant effect on the mechanical properties of the recycled Al alloys. In this work, hot compression tests of two [...] Read more.

It is unavoidable that Fe impurities will be mixed into Al alloys during recycling of automotive aluminum parts, and the Fe content has a significant effect on the mechanical properties of the recycled Al alloys. In this work, hot compression tests of two Fe-containing Al alloys were carried out at elevated temperatures within a wide strain rate range from 0.01 s⁻¹ to 10 s⁻¹. The effect of Fe content on the peak stress of the stress vs. strain curves, strain rate sensitivity and activation energy for dynamic recrystallization are analyzed. Results show that the recycled Al alloy containing 0.5 wt % Fe exhibits higher peak stresses and larger activation energy than the recycled Al alloy containing 0.1 wt % Fe, which results from the fact that there are more dispersed AlMgFeSi and/or AlFeSi precipitates in the recycled Al alloy containing 0.5 wt % Fe as confirmed by SEM observation and energy spectrum analysis. It is also shown that the Fe content has little effect on the strain rate sensitivity of the recycled Al alloys. Full article

(This article belongs to the Special Issue Light Weight Alloys: Processing, Properties and Their Applications)

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8439 KiB

Open AccessArticle

Characteristics of the Dynamic Recrystallization Behavior of Ti-45Al-8.5Nb-0.2W-0.2B-0.3Y Alloy during High Temperature Deformation

by Lin Xiang, Bin Tang, Xiangyi Xue, Hongchao Kou and Jinshan Li

Metals 2017, 7(7), 261; https://doi.org/10.3390/met7070261 - 8 Jul 2017

Cited by 13 | Viewed by 3905

Abstract

The dynamic recrystallization (DRX) behavior of Ti-45Al-8.5Nb-0.2W-0.2B-0.3Y (at %) alloy has been investigated through hot compression tests. The tests were executed at a temperature range of 1000–1200 °C and a strain rate range of 0.001–1 s⁻¹ under a true strain of 0.9. [...] Read more.

The dynamic recrystallization (DRX) behavior of Ti-45Al-8.5Nb-0.2W-0.2B-0.3Y (at %) alloy has been investigated through hot compression tests. The tests were executed at a temperature range of 1000–1200 °C and a strain rate range of 0.001–1 s⁻¹ under a true strain of 0.9. It was found that the α₂ phase which is produced during heat treatment is reduced during hot compression due to thermo-mechanical coupling. The value of the activation energy is 506.38 KJ/mol. With the increase in deformation temperature and the decrease in strain rate, DRX is more likely to occur, as a result of sufficient time and energy for the DRX process. Furthermore, the volume fraction of high angle grain boundaries increases to 89.01% at a temperature of 1200 °C and the strain rate of 0.001 s⁻¹, meaning completely dynamic recrystallization. In addition, DRX is related to the formation of twin boundaries. The volume fraction of twin boundaries rises to 16.93% at the same condition of completely dynamic recrystallization. Full article

(This article belongs to the Special Issue Light Weight Alloys: Processing, Properties and Their Applications)

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1953 KiB

Open AccessArticle

On the Invariance of Hardness at Vickers Indentation of Pre-Stressed Materials

by Per-Lennart Larsson

Metals 2017, 7(7), 260; https://doi.org/10.3390/met7070260 - 7 Jul 2017

Cited by 2 | Viewed by 4410

Abstract

The influence from residual surface stresses on global indentation properties, i.e., hardness and size of the contact area, have been studied quite frequently in recent years. A fundamental assumption when evaluating such tests is that the material hardness is independent of any residual [...] Read more.

The influence from residual surface stresses on global indentation properties, i.e., hardness and size of the contact area, have been studied quite frequently in recent years. A fundamental assumption when evaluating such tests is that the material hardness is independent of any residual stresses. This assumption has been verified in the case of cone indentation of classical Mises elastoplastic materials. However, a detailed investigation of this feature in the case of three-dimensional indentation, i.e., Vickers and Berkovic indentation, has not been presented previously. It is therefore the aim of the present study to remedy this shortcoming using finite element methods. The numerical results pertinent to Vickers indentation clearly show that the material hardness is independent of residual (or applied) stresses (also in case of three-dimensional indentation problems). The limitations of the validity of hardness invariance are also discussed in some detail. Full article

(This article belongs to the Special Issue Experimental Assessment of Residual Stress in Engineering Materials Components)

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5901 KiB

Open AccessArticle

Metallization of Extruded Briquettes (BREX) in Midrex Process

by Aitber Bizhanov and Tatyana Malysheva

Metals 2017, 7(7), 259; https://doi.org/10.3390/met7070259 - 7 Jul 2017

Cited by 6 | Viewed by 6234

Abstract

The results of the full-scale testing of the Extruded Briquettes (BREX) as the charge components of the industrial Midrex reactor are discussed. The influence of the type of binder on the degree of metallization of BREX is analyzed. Magnesium sulfate-based binder helps to [...] Read more.

The results of the full-scale testing of the Extruded Briquettes (BREX) as the charge components of the industrial Midrex reactor are discussed. The influence of the type of binder on the degree of metallization of BREX is analyzed. Magnesium sulfate-based binder helps to reach highest metallization degree of BREX. Mineralogical study shows the difference in the iron-silicate phase’s development as well as in the porosity change during metallization depending on the binder used. Full article

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5257 KiB

Open AccessArticle

Effect of Austempering Time on the Microstructure and Carbon Partitioning of Ultrahigh Strength Steel 56NiCrMoV7

by Quanshun Luo, Matthew Kitchen and Shahriar Abubakri

Metals 2017, 7(7), 258; https://doi.org/10.3390/met7070258 - 7 Jul 2017

Cited by 9 | Viewed by 7582

Abstract

Ultrahigh strength steel 56NiCrMoV7 was austempered at 270 °C for different durations in order to investigate the microstructure evolution, carbon partitioning behaviour and hardness property. Detailed microstructure has been characterised using optical microscopy and field emission gun scanning electron microscopy. A newly developed [...] Read more.

Ultrahigh strength steel 56NiCrMoV7 was austempered at 270 °C for different durations in order to investigate the microstructure evolution, carbon partitioning behaviour and hardness property. Detailed microstructure has been characterised using optical microscopy and field emission gun scanning electron microscopy. A newly developed X-ray diffraction method has been employed to dissolve the bainitic/martensitic ferrite phase as two sub-phases of different tetragonal ratios, which provides quantitative analyses of the carbon partitioning between the resultant ferrites and the retained austenite. The results show that, a short-term austempering treatment was in the incubation period of the bainite transformation, which resulted in maximum hardness being equivalent to the oil-quenching treatment. The associated microstructure comprises fine carbide-free martensitic and bainitic ferrites of supersaturated carbon contents as well as carbon-rich retained austenite. In particular, the short-term austempering treatment helped prevent the formation of lengthy martensitic laths as those being found in the microstructure of oil-quenched sample. When the austempering time was increased from 20 to 80 min, progressive decrease of the hardness was associated with the evolution of the microstructure, including progressive coarsening of bainitic ferrite, carbide precipitating inside high-carbon bainitic ferrite and its subsequent decarbonisation. Full article

(This article belongs to the Special Issue Bainite and Martensite: Developments and Challenges)

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632 KiB

Open AccessArticle

Localization Phenomena in Disordered Tantalum Films

by Natalia Kovaleva, Dagmar Chvostova and Alexandr Dejneka

Metals 2017, 7(7), 257; https://doi.org/10.3390/met7070257 - 7 Jul 2017

Cited by 5 | Viewed by 5536

Abstract

Using dc transport and wide-band spectroscopic ellipsometry techniques we study localization phenomena in highly disordered metallic

β

-Ta films grown by rf sputtering deposition. The dc transport study implies non-metallic behavior (d

ρ

/dT < 0), with negative temperature coefficient of resistivity [...] Read more.

Using dc transport and wide-band spectroscopic ellipsometry techniques we study localization phenomena in highly disordered metallic

β

-Ta films grown by rf sputtering deposition. The dc transport study implies non-metallic behavior (d

ρ

/dT < 0), with negative temperature coefficient of resistivity (TCR). We found that as the absolute TCR value increased, specifying an elevated degree of disorder, the free charge carrier Drude response decreases, indicating the enhanced charge carrier localization. Moreover, we found that the pronounced changes occur at the extended spectral range, involving not only the Drude resonance, but also the higher-energy Lorentz bands, in evidence of the attendant electronic correlations. We propose that the charge carrier localization, or delocalization, is accompanied by the pronounced electronic band structure reconstruction due to many-body effects, which may be the key feature for understanding the physics of highly disordered metals. Full article

(This article belongs to the Special Issue Bulk Metallic Glasses)

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9183 KiB

Open AccessArticle

A Finite Element Model to Simulate Defect Formation during Friction Stir Welding

by Zhi Zhu, Min Wang, Huijie Zhang, Xiao Zhang, Tao Yu and Zhenqiang Wu

Metals 2017, 7(7), 256; https://doi.org/10.3390/met7070256 - 7 Jul 2017

Cited by 63 | Viewed by 8645

Abstract

In this study, a 3D coupled thermo-mechanical finite element model is developed to predict and analyze the defect formation during friction stir welding based on coupled Eulerian Lagrangian method. The model is validated by comparing the estimated welding temperature, processed zone shape and [...] Read more.

In this study, a 3D coupled thermo-mechanical finite element model is developed to predict and analyze the defect formation during friction stir welding based on coupled Eulerian Lagrangian method. The model is validated by comparing the estimated welding temperature, processed zone shape and void size with those obtained experimentally. The results compared indicate that the simulated temperature and the data measured are in good agreement with each other. In addition, the model can predict the plasticized zone shape and the presence of a void in the weld quite accurately. However, the void size is overestimated. The effects of welding parameters and tool pin profile are also analyzed. The results reveal that welding at low welding speed or high tool rotational speed could produce a smaller void. Moreover, compared to a smooth tool pin, a featured tool pin can enhance plastic flow in the weld and achieve defect-free weldment. The results are helpful for the optimization of the welding process and the design of welding tools. Full article

(This article belongs to the Special Issue Recent Achievements in Rotary, Linear and Friction Stir Welding of Metals Alloys)

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9485 KiB

Open AccessFeature PaperArticle

Failure Assessment of Steel/CFRP Double Strap Joints

by Hamid Reza Majidi, Seyed Mohammad Javad Razavi and Filippo Berto

Metals 2017, 7(7), 255; https://doi.org/10.3390/met7070255 - 6 Jul 2017

Cited by 21 | Viewed by 6605

Abstract

In the current study, the failure behavior of retrofitted steel structures was studied experimentally and theoretically with steel/carbon fiber reinforced polymer (CFRP) double strap joints (DSJs) under quasi-static tensile loading. A series of DSJs with different bonding lengths are also considered and examined [...] Read more.

In the current study, the failure behavior of retrofitted steel structures was studied experimentally and theoretically with steel/carbon fiber reinforced polymer (CFRP) double strap joints (DSJs) under quasi-static tensile loading. A series of DSJs with different bonding lengths are also considered and examined to experimentally assess the effective bond length. To predict the failure load values of the tested specimens, a new stress-based method, namely the point stress (PS) method is proposed. Although some theoretical predictive modelling for the strength between steel/CFRP joints under various loading conditions has been presented, in this work by using the new proposed approach, one can calculate rapidly and conveniently the failure loads of the steel/CFRP specimens. Furthermore, to assess the validity of the new proposed method, further experimental data on steel/CFRP DSJs available in the open literature are predicted using the PS method. Finally, it was found that a good agreement exists between the experimental results and the theoretical predictions based on the PS method. Full article

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7942 KiB

Open AccessArticle

On the Short Surface Fatigue Crack Growth Behavior in a Fine-Grained WC-Co Cemented Carbide

by Hiroko Mikado, Sotomi Ishihara, Noriyasu Oguma and Shingo Kawamura

Metals 2017, 7(7), 254; https://doi.org/10.3390/met7070254 - 6 Jul 2017

Cited by 10 | Viewed by 6354

Abstract

In the present study, the fatigue crack growth (FCG) behavior of short surface cracks in a fine-grained cemented carbide with a length of less than 1 mm was investigated. The rotating bending and the four-point bending fatigue tests were carried out at stress [...] Read more.

In the present study, the fatigue crack growth (FCG) behavior of short surface cracks in a fine-grained cemented carbide with a length of less than 1 mm was investigated. The rotating bending and the four-point bending fatigue tests were carried out at stress ratios of R = −1 and R = 0.1 (R = maximum stress/minimum stress). It was found that a short surface crack had a longer stable fatigue crack growth area than a long through-thickness crack; the FCG behaviors of the two types of crack are clearly different. Furthermore, the FCG path of short surface cracks was investigated in detail to study the interaction between fatigue cracks and microstructures of the cemented carbide such as WC grains and the Co phase. At a low K_max (K_max = the maximum stress intensity factor), it was found that fatigue crack growth within WC grains is difficult because of a small driving force; instead, crack growth is along the brittle WC/WC interface. On the other hand, at a high K_max, WC grain breakage often occurs, since the driving force of FCG is large, and the fatigue crack grows linearly. Full article

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10235 KiB

Open AccessFeature PaperArticle

High-Temperature Tempered Martensite Embrittlement in Quenched-and-Tempered Offshore Steels

by Hung-Wei Yen, Meng-Hsuan Chiang, Yu-Chen Lin, Delphic Chen, Ching-Yuan Huang and Hsin-Chih Lin

Metals 2017, 7(7), 253; https://doi.org/10.3390/met7070253 - 6 Jul 2017

Cited by 27 | Viewed by 11746

Abstract

Embrittlement induced by high-temperature tempering was investigated in two quenched-and-tempered offshore steels. Electron backscattering diffraction and analysis of Kernel average misorientation were applied to study the coalescence of martensite; transmission Kikuchi diffraction coupled with compositional mapping was used to characterize the martensite/austenite (M/A) [...] Read more.

Embrittlement induced by high-temperature tempering was investigated in two quenched-and-tempered offshore steels. Electron backscattering diffraction and analysis of Kernel average misorientation were applied to study the coalescence of martensite; transmission Kikuchi diffraction coupled with compositional mapping was used to characterize the martensite/austenite (M/A) phases. It is suggested that the formation of lenticular martensite along prior austenite grain boundaries or packet boundaries primarily explains the embrittlement in conventional S690Q steel, which has a higher carbon content. This embrittlement can be cured by additional heat treatment to decompose martensite into ferrite and cementite. In a newly designed NiCu steel with reduced carbon content, new lath martensite formed along interlath or inter-block boundaries of prior martensite. This microstructure is less detrimental to the impact toughness of the steel. Full article

(This article belongs to the Special Issue Bainite and Martensite: Developments and Challenges)

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14092 KiB

Open AccessReview

Mg and Its Alloys for Biomedical Applications: Exploring Corrosion and Its Interplay with Mechanical Failure

by Mirco Peron, Jan Torgersen and Filippo Berto

Metals 2017, 7(7), 252; https://doi.org/10.3390/met7070252 - 5 Jul 2017

Cited by 113 | Viewed by 9884

Abstract

The future of biomaterial design will rely on temporary implant materials that degrade while tissues grow, releasing no toxic species during degradation and no residue after full regeneration of the targeted anatomic site. In this aspect, Mg and its alloys are receiving increasing [...] Read more.

The future of biomaterial design will rely on temporary implant materials that degrade while tissues grow, releasing no toxic species during degradation and no residue after full regeneration of the targeted anatomic site. In this aspect, Mg and its alloys are receiving increasing attention because they allow both mechanical strength and biodegradability. Yet their use as biomedical implants is limited due to their poor corrosion resistance and the consequential mechanical integrity problems leading to corrosion assisted cracking. This review provides the reader with an overview of current biomaterials, their stringent mechanical and chemical requirements and the potential of Mg alloys to fulfil them. We provide insight into corrosion mechanisms of Mg and its alloys, the fundamentals and established models behind stress corrosion cracking and corrosion fatigue. We explain Mgs unique negative differential effect and approaches to describe it. Finally, we go into depth on corrosion improvements, reviewing literature on high purity Mg, on the effect of alloying elements and their tolerance levels, as well as research on surface treatments that allow to tune degradation kinetics. Bridging fundamentals aspects with current research activities in the field, this review intends to give a substantial overview for all interested readers; potential and current researchers and practitioners of the future not yet familiar with this promising material. Full article

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