Metals

19437 KiB

Open AccessArticle

Direct Metal Laser Sintering of Ti6Al4V for Biomedical Applications: Microstructure, Corrosion Properties, and Mechanical Treatment of Implants

by Janette Brezinová, Radovan Hudák, Anna Guzanová, Dagmar Draganovská, Gabriela Ižaríková and Juraj Koncz

Metals 2016, 6(7), 171; https://doi.org/10.3390/met6070171 - 20 Jul 2016

Cited by 34 | Viewed by 6377

Abstract

Ti6Al4V samples have been prepared by Direct Metal Laser Sintering (DMLS) with varied laser power. Some of the samples were stress-relief annealed. The microstructure of materials was investigated using a light microscopy. Columnar grains of martensite dominate in as-made microstructure. Stress-relief annealing led [...] Read more.

Ti6Al4V samples have been prepared by Direct Metal Laser Sintering (DMLS) with varied laser power. Some of the samples were stress-relief annealed. The microstructure of materials was investigated using a light microscopy. Columnar grains of martensite dominate in as-made microstructure. Stress-relief annealing led to the white acicular phase growth in the structure with a fishbone arrangement on the boundary of some original martensitic needles. Mechanical properties of materials were characterized through hardness measurement in two directions relating to the sample building direction. It was found that the hardness of materials increased with a laser power and values varied from 370 to 415 HV 0.3/30. After stress-relief annealing, the structure of materials being homogenized, pattern spacing dissolved and the hardness in both directions became stabilized at values of 350–370 HV 0.3/30. The laser power affects the corrosion rate of the material. The lowest corrosion rate was recorded at the maximum laser power (190 W). Heat treatment does not affect the corrosion rate remarkably, however it leads to stabilization of corrosion potential of materials Ecorr. The surface of the samples was modified by an abrasive blasting using spherical (zirblast) and sharp-edged (white corundum) blasting abrasives and three levels of air pressure. The abrasive blasting of sintered materials led to a decrease of the surface roughness of materials with air pressure increasing. Blasting with zirblast led to a more significant decrease of roughness parameters compared with surfaces blasted with sharp-edged white aluminum. Different shapes of abrasives caused characteristic surface morphology. Full article

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3793 KiB

Open AccessArticle

Comparative Study on the Grain Refinement of Al-Si Alloy Solidified under the Impact of Pulsed Electric Current and Travelling Magnetic Field

by Yunhu Zhang, Xiangru Cheng, Honggang Zhong, Zhishuai Xu, Lijuan Li, Yongyong Gong, Xincheng Miao, Changjiang Song and Qijie Zhai

Metals 2016, 6(7), 170; https://doi.org/10.3390/met6070170 - 20 Jul 2016

Cited by 32 | Viewed by 5390

Abstract

It is high of commercial importance to generate the grain refinement in alloys during solidification by means of electromagnetic fields. Two typical patterns of electromagnetic fields, pulsed electric currents (ECP) and traveling magnetic field (TMF), are frequently employed to produce the finer equiaxed [...] Read more.

It is high of commercial importance to generate the grain refinement in alloys during solidification by means of electromagnetic fields. Two typical patterns of electromagnetic fields, pulsed electric currents (ECP) and traveling magnetic field (TMF), are frequently employed to produce the finer equiaxed grains in solidifying alloys. Various mechanisms were proposed to understand the grain refinement in alloys caused by ECP and TMF. In this paper, a comparative study is carried out in the same solidification regime to investigate the grain refinement of Al-7 wt. %Si alloy driven by ECP and TMF. Experimental results show that the application of ECP or TMF can cause the same grain refinement occurrence period, during which the refinement of primary Al continuously occurs. In addition, the related grain refinement mechanisms are reviewed and discussed, which shows the most likely one caused by ECP and TMF is the promoted dendrite fragmentation as the result of the ECP-induced or TMF-induced forced flow. It suggests that the same grain refinement process in alloys is provoked when ECP and TMF are applied in the same solidification regime, respectively. Full article

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6968 KiB

Open AccessArticle

Effect of Hydrogen and Strain-Induced Martensite on Mechanical Properties of AISI 304 Stainless Steel

by Sang Hwan Bak, Muhammad Ali Abro and Dong Bok Lee

Metals 2016, 6(7), 169; https://doi.org/10.3390/met6070169 - 20 Jul 2016

Cited by 25 | Viewed by 7662

Abstract

Plastic deformation and strain-induced martensite (SIM, α′) transformation in metastable austenitic AISI 304 stainless steel were investigated through room temperature tensile tests at strain rates ranging from 2 × 10⁻⁶ to 2 × 10⁻²/s. The amount of SIM was measured [...] Read more.

Plastic deformation and strain-induced martensite (SIM, α′) transformation in metastable austenitic AISI 304 stainless steel were investigated through room temperature tensile tests at strain rates ranging from 2 × 10⁻⁶ to 2 × 10⁻²/s. The amount of SIM was measured on the fractured tensile specimens using a feritscope and magnetic force microscope. Elongation to fracture, tensile strength, hardness, and the amount of SIM increased with decreasing the strain rate. The strain-rate dependence of RT tensile properties was observed to be related to the amount of SIM. Specifically, SIM formed during tensile tests was beneficial in increasing the elongation to fracture, hardness, and tensile strength. Hydrogen suppressed the SIM formation, leading to hydrogen softening and localized brittle fracture. Full article

(This article belongs to the Special Issue Process-Structure-Property Relationships in Metals)

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226 KiB

Open AccessReview

The Development of Coronary Artery Stents: From Bare-Metal to Bio-Resorbable Types

by Ming-Yun Ho, Chun-Chi Chen, Chao-Yung Wang, Shang-Hung Chang, Ming-Jer Hsieh, Cheng-Hung Lee, Victor Chien-Chia Wu and I-Chang Hsieh

Metals 2016, 6(7), 168; https://doi.org/10.3390/met6070168 - 20 Jul 2016

Cited by 35 | Viewed by 8880

Abstract

Coronary artery disease is the leading cause of death worldwide. Conventional balloon angioplasty is associated with high rates of complications such as coronary dissection and vessel recoil. The deployment of bare-metal stents (BMSs) can overcome these problems and achieve a better patency rate [...] Read more.

Coronary artery disease is the leading cause of death worldwide. Conventional balloon angioplasty is associated with high rates of complications such as coronary dissection and vessel recoil. The deployment of bare-metal stents (BMSs) can overcome these problems and achieve a better patency rate than simple balloon angioplasty. It has been shown that the stent design including structure platform, size, length, and strut thickness has a major influence on the clinical results. Even though angioplasty with BMS implantation is widely used in coronary interventions, the restenosis rate due to neointimal hyperplasia remains high. Therefore, drug-eluting stents (DESs) coated with anti-proliferative agents and polymers have been developed to reduce the restenosis rate and improve the clinical outcomes. Although the repeat revascularization rate of DESs is lower than that of BMSs, the long-term stent thrombosis rate is higher than for BMSs. Therefore, new and emerging generations of stents, in which, for example, thinner struts and bioresorbable polymers are used, are available for clinical use. However, there are only a limited number of clinical trials, in which these newer stents have been compared with BMSs and first- and second-generation DESs. The purpose of this review was to provide up-to-date information on the evolution of coronary artery stents from BMSs to DESs to bioresorbable stents (BRSs). Full article

(This article belongs to the Special Issue Metallic Biomaterials)

17711 KiB

Open AccessFeature PaperArticle

Atmospheric-Induced Stress Corrosion Cracking of Grade 2205 Duplex Stainless Steel—Effects of 475 °C Embrittlement and Process Orientation

by Cem Örnek, Safwan A.M. Idris, Pierfranco Reccagni and Dirk L. Engelberg

Metals 2016, 6(7), 167; https://doi.org/10.3390/met6070167 - 19 Jul 2016

Cited by 26 | Viewed by 7849

Abstract

The effect of 475 °C embrittlement and microstructure process orientation on atmospheric-induced stress corrosion cracking (AISCC) of grade 2205 duplex stainless steel has been investigated. AISCC tests were carried out under salt-laden, chloride-containing deposits, on U-bend samples manufactured in rolling (RD) and transverse [...] Read more.

The effect of 475 °C embrittlement and microstructure process orientation on atmospheric-induced stress corrosion cracking (AISCC) of grade 2205 duplex stainless steel has been investigated. AISCC tests were carried out under salt-laden, chloride-containing deposits, on U-bend samples manufactured in rolling (RD) and transverse directions (TD). The occurrence of selective corrosion and stress corrosion cracking was observed, with samples in TD displaying higher propensity towards AISCC. Strains and tensile stresses were observed in both ferrite and austenite, with similar magnitudes in TD, whereas, larger strains and stresses in austenite in RD. The occurrence of 475 °C embrittlement was related to microstructural changes in the ferrite. Exposure to 475 °C heat treatment for 5 to 10 h resulted in better AISCC resistance, with spinodal decomposition believed to enhance the corrosion properties of the ferrite. The austenite was more susceptible to ageing treatments up to 50 h, with the ferrite becoming more susceptible with ageing in excess of 50 h. Increased susceptibility of the ferrite may be related to the formation of additional precipitates, such as R-phase. The implications of heat treatment at 475 °C and the effect of process orientation are discussed in light of microstructure development and propensity to AISCC. Full article

(This article belongs to the Special Issue Process-Structure-Property Relationships in Metals)

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6286 KiB

Open AccessArticle

Specific Yielding of Selective Laser-Melted Ti6Al4V Open-Porous Scaffolds as a Function of Unit Cell Design and Dimensions

by Volker Weißmann, Jan Wieding, Harald Hansmann, Nico Laufer, Andreas Wolf and Rainer Bader

Metals 2016, 6(7), 166; https://doi.org/10.3390/met6070166 - 18 Jul 2016

Cited by 34 | Viewed by 6805

Abstract

Bone loss in the near-vicinity of implants can be a consequence of stress shielding due to stiffness mismatch. This can be avoided by reducing implant stiffness, i.e., by implementing an open-porous structure. Three open-porous designs were therefore investigated (cubic, pyramidal and a twisted [...] Read more.

Bone loss in the near-vicinity of implants can be a consequence of stress shielding due to stiffness mismatch. This can be avoided by reducing implant stiffness, i.e., by implementing an open-porous structure. Three open-porous designs were therefore investigated (cubic, pyramidal and a twisted design). Scaffolds were fabricated by a selective laser-melting (SLM) process and material properties were determined by conducting uniaxial compression testing. The calculated elastic modulus values for the scaffolds varied between 3.4 and 26.3 GP and the scaffold porosities between 43% and 80%. A proportional linear correlation was found between the elastic modulus and the geometrical parameters, between the elastic modulus and the compressive strengths, as well as between the strut width-to-diameter ratio (a/d) and elastic modulus. Furthermore, we found a power-law relationship between porosity and the modulus of elasticity that characterizes specific yielding. With respect to scaffold porosity, the description of specific yielding behaviour offers a simple way to characterize the mechanical properties of open-porous structures and helps generate scaffolds with properties specific to their intended application. A direct comparison with human bone parameters is also possible. We generated scaffolds with mechanical properties sufficiently close to that of human cortical bone. Full article

(This article belongs to the Special Issue Metallic Biomaterials)

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6085 KiB

Open AccessArticle

Hydrostatic Compression Behavior and High-Pressure Stabilized β-Phase in γ-Based Titanium Aluminide Intermetallics

by Klaus-Dieter Liss, Ken-Ichi Funakoshi, Rian Johannes Dippenaar, Yuji Higo, Ayumi Shiro, Mark Reid, Hiroshi Suzuki, Takahisa Shobu and Koichi Akita

Metals 2016, 6(7), 165; https://doi.org/10.3390/met6070165 - 15 Jul 2016

Cited by 21 | Viewed by 6603 | Correction

Abstract

Titanium aluminides find application in modern light-weight, high-temperature turbines, such as aircraft engines, but suffer from poor plasticity during manufacturing and processing. Huge forging presses enable materials processing in the 10-GPa range, and hence, it is necessary to investigate the phase diagrams of [...] Read more.

Titanium aluminides find application in modern light-weight, high-temperature turbines, such as aircraft engines, but suffer from poor plasticity during manufacturing and processing. Huge forging presses enable materials processing in the 10-GPa range, and hence, it is necessary to investigate the phase diagrams of candidate materials under these extreme conditions. Here, we report on an in situ synchrotron X-ray diffraction study in a large-volume press of a modern (α₂ + γ) two-phase material, Ti-45Al-7.5Nb-0.25C, under pressures up to 9.6 GPa and temperatures up to 1686 K. At room temperature, the volume response to pressure is accommodated by the transformation γ → α₂, rather than volumetric strain, expressed by the apparently high bulk moduli of both constituent phases. Crystallographic aspects, specifically lattice strain and atomic order, are discussed in detail. It is interesting to note that this transformation takes place despite an increase in atomic volume, which is due to the high ordering energy of γ. Upon heating under high pressure, both the eutectoid and γ-solvus transition temperatures are elevated, and a third, cubic β-phase is stabilized above 1350 K. Earlier research has shown that this β-phase is very ductile during plastic deformation, essential in near-conventional forging processes. Here, we were able to identify an ideal processing window for near-conventional forging, while the presence of the detrimental β-phase is not present under operating conditions. Novel processing routes can be defined from these findings. Full article

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

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7151 KiB

Open AccessFeature PaperArticle

Classification of Induced Magnetic Field Signals for the Microstructural Characterization of Sigma Phase in Duplex Stainless Steels

by Edgard M. Silva, Leandro B. Marinho, Pedro P. Rebouças Filho, João P. Leite, Josinaldo P. Leite, Walter M. L. Fialho, Victor Hugo C. De Albuquerque and João Manuel R. S. Tavares

Metals 2016, 6(7), 164; https://doi.org/10.3390/met6070164 - 14 Jul 2016

Cited by 14 | Viewed by 5499

Abstract

Duplex stainless steels present excellent mechanical and corrosion resistance properties. However, when heat treated at temperatures above 600

^{\circ}

C, the undesirable tertiary sigma phase is formed. This phase presents high hardness, around 900 HV, and it is rich in chromium, the material [...] Read more.

Duplex stainless steels present excellent mechanical and corrosion resistance properties. However, when heat treated at temperatures above 600

^{\circ}

C, the undesirable tertiary sigma phase is formed. This phase presents high hardness, around 900 HV, and it is rich in chromium, the material toughness being compromised when the amount of this phase is not less than 4%. This work aimed to develop a solution for the detection of this phase in duplex stainless steels through the computational classification of induced magnetic field signals. The proposed solution is based on an Optimum Path Forest classifier, which was revealed to be more robust and effective than Bayes, Artificial Neural Network and Support Vector Machine based classifiers. The induced magnetic field was produced by the interaction between an applied external field and the microstructure. Samples of the 2205 duplex stainless steel were thermal aged in order to obtain different amounts of sigma phases (up to 18% in content). The obtained classification results were compared against the ones obtained by Charpy impact energy test, amount of sigma phase, and analysis of the fracture surface by scanning electron microscopy and X-ray diffraction. The proposed solution achieved a classification accuracy superior to 95% and was revealed to be robust to signal noise, being therefore a valid testing tool to be used in this domain. Full article

(This article belongs to the Special Issue Non-Destructive Metallic Materials Testing—Recent Research and Future Perspectives)

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5687 KiB

Open AccessArticle

Failure Analysis of High Strength Galvanized Bolts Used in Steel Towers

by Jose Alberto Álvarez, Roberto Lacalle, Borja Arroyo, Sergio Cicero and Federico Gutiérrez-Solana

Metals 2016, 6(7), 163; https://doi.org/10.3390/met6070163 - 13 Jul 2016

Cited by 22 | Viewed by 7571

Abstract

This paper analyses the failure of three bolts used in the structural connections of a number of steel towers located in northern Europe. The analysis comprises optical and scanning electron microscopy, microstructural and hardness analysis, mechanical testing and structural integrity assessments. The three [...] Read more.

This paper analyses the failure of three bolts used in the structural connections of a number of steel towers located in northern Europe. The analysis comprises optical and scanning electron microscopy, microstructural and hardness analysis, mechanical testing and structural integrity assessments. The three bolts present very similar failure processes, with a circumferential external crack that led to the final failure. The morphology of the crack propagation is typical of Hydrogen-Induced Stress Corrosion Cracking (HISCC), with mixed intergranular-transgranular micromechanisms, tearing processes and secondary cracking. The cracks then grew subcritically until they reached their critical size. Quench cracking or fatigue processes have been ruled out. Full article

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3120 KiB

Open AccessArticle

Preparation and Analysis of Complex Barrier Layer of Heterocyclic and Long-Chain Organosilane on Copper Alloy Surface

by Qian Zhao, Tiantian Tang, Peilin Dang, Zhiyi Zhang and Fang Wang

Metals 2016, 6(7), 162; https://doi.org/10.3390/met6070162 - 13 Jul 2016

Cited by 6 | Viewed by 4177

Abstract

A single electrodeposited film of 6-(3-triethoxysilylpropyl)amino-1,3,5-triazine-2,4-dithiol monosodium (TES) on a copper alloy surface was prepared by the galvanostatic method, then octyl-triethoxysilane (OTES) or hexadecyl-trimethoxysilane (HDTMS) was used to modify the electrodeposited film by the self-assembled technique to fabricate the complex film. The electrodeposition [...] Read more.

A single electrodeposited film of 6-(3-triethoxysilylpropyl)amino-1,3,5-triazine-2,4-dithiol monosodium (TES) on a copper alloy surface was prepared by the galvanostatic method, then octyl-triethoxysilane (OTES) or hexadecyl-trimethoxysilane (HDTMS) was used to modify the electrodeposited film by the self-assembled technique to fabricate the complex film. The electrodeposition process was inferred by cyclic voltammetry. The single and complex films were characterized by means of contact angle, cyclic voltammetry, Fourier transform infrared spectroscopy (FT-IR), potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and scanning electron microscope (SEM). The results showed that the contact angle of the complex film covering the copper alloy surface was up to 118.1° compared with 89.4° of the bare copper alloy. The cyclic voltammogram, polarization curves and EIS indicated that the anti-corrosion performance of complex film was better than that of single electrodeposited TES film, and the protection efficiency was up to 90.2%. Full article

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6798 KiB

Open AccessArticle

Constitutive Model Based on Dynamic Recrystallization Behavior during Thermal Deformation of a Nickel-Based Superalloy

by Peng Zhang, Cen Yi, Gang Chen, Heyong Qin and Chuanjie Wang

Metals 2016, 6(7), 161; https://doi.org/10.3390/met6070161 - 13 Jul 2016

Cited by 46 | Viewed by 6518

Abstract

The thermal deformation and dynamic recrystallization (DRX) behavior of a nickel-based superalloy were investigated by the thermal compression test. The experimental results show that the process parameters have great influence on the flow stress of the superalloy. In addition, there is an inflection [...] Read more.

The thermal deformation and dynamic recrystallization (DRX) behavior of a nickel-based superalloy were investigated by the thermal compression test. The experimental results show that the process parameters have great influence on the flow stress of the superalloy. In addition, there is an inflection point on the DRX softening stage of the work-hardening rate versus stress curve. DRX under the conditions of higher temperatures and lower strain rates easily occurs when the strain reaches a critical level. Based on the classical dislocation density theory and the DRX kinetics models, a two-stage constitutive model considering the effect of work hardening-dynamic recovery and DRX is developed for the superalloy. Comparisons between the predicted and experimental data indicate that the values predicted by the proposed constitutive model are in good agreement with the experimental results. Full article

(This article belongs to the Special Issue Ni- and Co-Based Superalloys and Their Coatings)

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3840 KiB

Open AccessArticle

The Effects of Corrosive Media on Fatigue Performance of Structural Aluminum Alloys

by Huihui Yang, Yanling Wang, Xishu Wang, Pan Pan and Dawei Jia

Metals 2016, 6(7), 160; https://doi.org/10.3390/met6070160 - 13 Jul 2016

Cited by 19 | Viewed by 6095

Abstract

The effects of corrosive media on rotating bending fatigue lives (the cyclic numbers from 10⁴ to 10⁸) of different aluminum alloys were investigated, which involved the corrosion fatigue lives of five kinds of aluminum alloys in air, at 3.5 wt. [...] Read more.

The effects of corrosive media on rotating bending fatigue lives (the cyclic numbers from 10⁴ to 10⁸) of different aluminum alloys were investigated, which involved the corrosion fatigue lives of five kinds of aluminum alloys in air, at 3.5 wt. % and 5.0 wt. % NaCl aqueous solutions. Experimental results indicate that corrosive media have different harmful influences on fatigue lives of different aluminum alloys, in which the differences of corrosion fatigue lives depend strongly on the plastic property (such as the elongation parameter) of aluminum alloys and whether to exist with and without fracture mode II. The other various influence factors (such as the dropping corrosive liquid rate, the loading style, and the nondimensionalization of strength) of corrosion fatigue lives in three media were also discussed in detail by using the typical cases. Furthermore, fracture morphologies and characteristics of samples, which showed the different fatigue cracking behaviors of aluminum alloys in three media, were investigated by scanning electron microscopy (SEM) in this paper. Full article

(This article belongs to the Special Issue Fatigue Damage)

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5481 KiB

Open AccessFeature PaperArticle

Contact Properties and Wear Behaviour of Nickel Based Superalloy René 80

by Mario Lavella

Metals 2016, 6(7), 159; https://doi.org/10.3390/met6070159 - 12 Jul 2016

Cited by 30 | Viewed by 6463

Abstract

A superalloy traditionally offers excellent mechanical strength, resistance to thermal creep deformation, good surface stability and resistance to corrosion or oxidation. However, a superalloy often also needs performance in terms of fretting resistance. Experimental results regarding fretting wear and contact properties of the [...] Read more.

A superalloy traditionally offers excellent mechanical strength, resistance to thermal creep deformation, good surface stability and resistance to corrosion or oxidation. However, a superalloy often also needs performance in terms of fretting resistance. Experimental results regarding fretting wear and contact properties of the superalloy René 80 are illustrated and discussed. The widespread applications of superalloys in jointing with friction as in the jointing of a turbine blade, is the main motivation for characterizing their fretting behaviour. The fretting experiments were performed at 100 Hz for two temperatures (600, 800 °C), and two sliding amplitudes (30, 60 µm). These temperatures and strokes are typical at the medium stage of a low-pressure gas turbine. Wear volume and the contact properties such as friction coefficient and tangential contact stiffness were measured and analysed. Results show that the lowest friction coefficient was measured at the temperature of 800 °C. This temperature hence appears to be an optimum working condition for the fretting wear of René 80. With regard to wear mechanism, a fundamental role of the sliding amplitude was found. In particular, the ratio between the sliding amplitude and the characteristic contact length has a significant influence upon the oxide growth on contact surfaces. Full article

(This article belongs to the Special Issue Ni- and Co-Based Superalloys and Their Coatings)

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3152 KiB

Open AccessFeature PaperArticle

Substructural Alignment during ECAE Processing of an Al-0.1Mg Aluminium Alloy

by Yan Huang

Metals 2016, 6(7), 158; https://doi.org/10.3390/met6070158 - 12 Jul 2016

Cited by 13 | Viewed by 4717

Abstract

An investigation has been carried out into the microstructures developed during the early stages of equal channel angular extrusion (ECAE) in a polycrystalline single-phase Al-0.13Mg alloy, with emphasis on the substructural alignment with respect to the die geometry and the crystallographic slip systems, [...] Read more.

An investigation has been carried out into the microstructures developed during the early stages of equal channel angular extrusion (ECAE) in a polycrystalline single-phase Al-0.13Mg alloy, with emphasis on the substructural alignment with respect to the die geometry and the crystallographic slip systems, which is essentially related to the grain refinement and texture development during deformation. The material was processed by ECAE at room temperature to three passes, via a 90° die. Microstructures were examined and characterized by EBSD. It was found that dislocation cell bands and microshear bands were respectively the most characteristic deformation structures of the first and second pass ECAE. Both formed across the whole specimen and to align approximately with the die shear plane, regardless of the orientation of individual grains. This confirmed that substructural alignment was in response to the direction of the maximum resolved shear stress rather than to the crystallographic slip systems. However, a significant fraction of material developed preferred orientations during deformation that allowed the coincidence between the crystallographic slip systems and the simple shear geometry to occur, which governed texture development in the material. The third pass deformation was characterized with the formation of a fibre structure with a significant fraction of high angle boundaries, being aligned at an angle to the extrusion direction, which was determined by the total shear strain applied. Full article

(This article belongs to the Special Issue Aluminum Alloys)

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7120 KiB

Open AccessArticle

The Effect of Chromium on the Roasting Process of Vanadium Extraction

by Dong Liu, Xiangxin Xue and He Yang

Metals 2016, 6(7), 157; https://doi.org/10.3390/met6070157 - 09 Jul 2016

Cited by 8 | Viewed by 4691

Abstract

We simulated the roasting process of chromium by mixing Cr₂O₃ and Na₂CO₃ to analyze the influence of chromium on roasting vanadium slag. Samples were characterized by XRD, thermal analysis and SEM at different temperatures: Cr₂O [...] Read more.

We simulated the roasting process of chromium by mixing Cr₂O₃ and Na₂CO₃ to analyze the influence of chromium on roasting vanadium slag. Samples were characterized by XRD, thermal analysis and SEM at different temperatures: Cr₂O₃ and Na₂CO₃ began to react at 500 °C. When the chromium oxide content was about 3.2%, the conversion rate of V reached the maximum value of 95%. Full article

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2849 KiB

Open AccessArticle

First-Principles Study on the Structural Stability and Segregation Behavior of γ-Fe/Cr₂N Interface with Alloying Additives M (M = Mn, V, Ti, Mo, and Ni)

by Hui Huang, Caili Zhang, Jie Liu, Yue Li, Xudong Fang, Jianchun Li and Peide Han

Metals 2016, 6(7), 156; https://doi.org/10.3390/met6070156 - 09 Jul 2016

Cited by 16 | Viewed by 5072

Abstract

This study investigated the structural stability and electrochemical properties of alloying additives M (M = Mn, V, Ti, Mo, or Ni) at the γ-Fe(111)/Cr₂N(0001) interface by the first-principles method. Results indicated that V and Ti were easily segregated at the γ-Fe(111)/Cr [...] Read more.

This study investigated the structural stability and electrochemical properties of alloying additives M (M = Mn, V, Ti, Mo, or Ni) at the γ-Fe(111)/Cr₂N(0001) interface by the first-principles method. Results indicated that V and Ti were easily segregated at the γ-Fe(111)/Cr₂N(0001) interface and enhanced interfacial adhesive strength. By contrast, Ni and Mo were difficult to segregate at the γ-Fe(111)/Cr₂N(0001) interface. Moreover, the results of the work function demonstrated that alloying additives Mn reduced local electrochemical corrosion behavior of the γ-Fe(111)/Cr₂N(0001) interface by cutting down Volta potential difference (VPD) between clean γ-Fe(111) and Cr₂N(0001), while alloying additives V, Ti, Mo, and Ni at the γ-Fe(111)/Cr₂N(0001) interface magnified VPD between clean γ-Fe(111) and Cr₂N(0001), which were low-potential sites that usually serve as local attack initiation points. Full article

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6477 KiB

Open AccessArticle

Gas Metal Arc Welding Using Novel CaO-Added Mg Alloy Filler Wire

by Minjung Kang, Youngnam Ahn and Cheolhee Kim

Metals 2016, 6(7), 155; https://doi.org/10.3390/met6070155 - 08 Jul 2016

Cited by 2 | Viewed by 5036

Abstract

Novel “ECO Mg” alloys, i.e., CaO-added Mg alloys, which exhibit oxidation resistance during melting and casting processes, even without the use of beryllium or toxic protection gases such as SF₆, have recently been introduced. Research on ECO Mg alloys is still [...] Read more.

Novel “ECO Mg” alloys, i.e., CaO-added Mg alloys, which exhibit oxidation resistance during melting and casting processes, even without the use of beryllium or toxic protection gases such as SF₆, have recently been introduced. Research on ECO Mg alloys is still continuing, and their application as welding filler metals was investigated in this study. Mechanical and metallurgical aspects of the weldments were analysed after welding, and welding behaviours such as fume generation and droplet transfer were observed during welding. The tensile strength of welds was slightly increased by adding CaO to the filler metal, which resulted from the decreased grain size in the weld metal. When welding Mg alloys, fumes have been unavoidable so far because of the low boiling temperature of Mg. Fume reduction was successfully demonstrated with a wire composed of the novel ECO Mg filler. In addition, stable droplet transfer was observed and spatter suppression could be expected by using CaO-added Mg filler wire. Full article

(This article belongs to the Special Issue Advances in Welding Metal Alloys, Dissimilar Metals and Additively Manufactured Parts)

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3413 KiB

Open AccessArticle

Cobalt-Nickel-Boron Supported over Polypyrrole-Derived Activated Carbon for Hydrolysis of Ammonia Borane

by Yongjin Zou, Yubo Gao, Cuili Xiang, Hailiang Chu, Shujun Qiu, Erhu Yan, Fen Xu, Chengying Tang and Lixian Sun

Metals 2016, 6(7), 154; https://doi.org/10.3390/met6070154 - 08 Jul 2016

Cited by 21 | Viewed by 5990

Abstract

In this study, polypyrrole (PPy) nanofibers were used to synthesize a super-activated carbon material. A highly-dispersed Co-Ni-B catalyst was supported on PPy nanofiber-derived activated carbon (PAC) by chemical reduction. The Co-Ni-B/PAC hybrid catalyst exhibited excellent catalytic performance for the decomposition of ammonia borane [...] Read more.

In this study, polypyrrole (PPy) nanofibers were used to synthesize a super-activated carbon material. A highly-dispersed Co-Ni-B catalyst was supported on PPy nanofiber-derived activated carbon (PAC) by chemical reduction. The Co-Ni-B/PAC hybrid catalyst exhibited excellent catalytic performance for the decomposition of ammonia borane (AB) in an aqueous alkaline solution at room temperature. The size of the metal particles, morphology of Co-Ni-B/PAC, and catalytic activity of the supported catalyst were investigated. Ni-B, Co-B, and Co-Ni-B catalysts were also synthesized in the absence of PAC under similar conditions for comparison. The maximum hydrogen generation rate (1451.2 mL⁻¹·min⁻¹·g⁻¹ at 25 °C) was obtained with Co-Ni-B/PAC. Kinetic studies indicated that the hydrolysis reaction of AB was first order with respect to Co-Ni-B/PAC, and the activation energy was 30.2 kJ·mol⁻¹. Even after ten recycling experiments, the catalyst showed good stability owing to the synergistic effect of Co-Ni-B and PAC. Full article

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2684 KiB

Open AccessArticle

One-Step Extraction of Antimony in Low Temperature from Stibnite Concentrate Using Iron Oxide as Sulfur-Fixing Agent

by Yun Li, Yongming Chen, Haotian Xue, Chaobo Tang, Shenghai Yang and Motang Tang

Metals 2016, 6(7), 153; https://doi.org/10.3390/met6070153 - 07 Jul 2016

Cited by 17 | Viewed by 8045

Abstract

A new process for one-step extraction of antimony in low temperature from stibnite concentrate by reductive sulfur-fixation smelting in sodium molten salt, using iron oxide as sulfur-fixing agent, was presented. The influences of molten salt addition and composition, ferric oxide dosage, smelting temperature [...] Read more.

A new process for one-step extraction of antimony in low temperature from stibnite concentrate by reductive sulfur-fixation smelting in sodium molten salt, using iron oxide as sulfur-fixing agent, was presented. The influences of molten salt addition and composition, ferric oxide dosage, smelting temperature and duration on extraction efficiency of antimony were investigated in details, respectively. The optimum conditions were determined as follows: 1.0 time stoichiometric requirement (α) of mixed sodium salt (α_salt = 1.0), W_NaCl:W_salt = 40%, α_Fe₂O₃ = 1.0, W_coke:W_stibnite = 40%, where W represents weight, smelting at 850 °C (1123 K) for 60 min. Under the optimum conditions, the direct recovery rate of antimony can reach 91.48%, and crude antimony with a purity of 96.00% has been achieved. 95.31% of sulfur is fixed in form of FeS in the presence of iron oxide. Meanwhile, precious metals contained in stibnite concentrate are enriched and recovered comprehensively in crude antimony. In comparison to traditional antimony pyrometallurgical process, the smelting temperature of present process is reduced from 1150–1200 °C (1423–1473 K) to 850–900 °C (1123–1173 K). Sulfur obtained in stibnite is fixed in FeS which avoids SO₂ emission owing to the sulfur-fixing agent. Sodium salt can be regenerated and recycled in smelting system when the molten slag is operated to filter solid residue. The solid residue is subjected to mineral dressing operation to obtain iron sulfide concentrate which can be sold directly or roasted to regenerate into iron oxide. Full article

(This article belongs to the Special Issue Recycling of Metals)

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4358 KiB

Open AccessArticle

Dynamic Recrystallization and Hot Workability of 316LN Stainless Steel

by Chaoyang Sun, Yu Xiang, Qingjun Zhou, Denis J. Politis, Zhihui Sun and Mengqi Wang

Metals 2016, 6(7), 152; https://doi.org/10.3390/met6070152 - 05 Jul 2016

Cited by 19 | Viewed by 5710

Abstract

To identify the optimal deformation parameters for 316LN austenitic stainless steel, it is necessary to study the macroscopic deformation and the microstructural evolution behavior simultaneously in order to ascertain the relationship between the two. Isothermal uniaxial compression tests of 316LN were conducted over [...] Read more.

To identify the optimal deformation parameters for 316LN austenitic stainless steel, it is necessary to study the macroscopic deformation and the microstructural evolution behavior simultaneously in order to ascertain the relationship between the two. Isothermal uniaxial compression tests of 316LN were conducted over the temperature range of 950–1150 °C and for the strain rate range of 0.001–10 s⁻¹ using a Gleeble-1500 thermal-mechanical simulator. The microstructural evolution during deformation processes was investigated by studying the constitutive law and dynamic recrystallization behaviors. Dynamic recrystallization volume fraction was introduced to reveal the power dissipation during the microstructural evolution. Processing maps were developed based on the effects of various temperatures, strain rates, and strains, which suggests that power dissipation efficiency increases gradually with increasing temperature and decreasing stain rate. Optimum regimes for the hot deformation of 316LN stainless steel were revealed on conventional hot processing maps and verified effectively through the examination of the microstructure. In addition, the regimes for defects of the product were also interpreted on the conventional hot processing maps. The developed power dissipation efficiency maps allow optimized processing routes to be selected, thus enabling industry producers to effectively control forming variables to enhance practical production process efficiency. Full article

(This article belongs to the Special Issue Process-Structure-Property Relationships in Metals)

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4844 KiB

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The Potential of Acousto-Ultrasonic Techniques for Inspection of Baked Carbon Anodes

by Moez Ben Boubaker, Donald Picard, Carl Duchesne, Jayson Tessier, Houshang Alamdari and Mario Fafard

Metals 2016, 6(7), 151; https://doi.org/10.3390/met6070151 - 04 Jul 2016

Cited by 8 | Viewed by 4385

Abstract

High quality baked carbon anodes contribute to the optimal performance of aluminum reduction cells. However, the currently decreasing quality and increasing variability of anode raw materials (coke and pitch) make it challenging to manufacture the anodes with consistent overall quality. Intercepting faulty anodes [...] Read more.

High quality baked carbon anodes contribute to the optimal performance of aluminum reduction cells. However, the currently decreasing quality and increasing variability of anode raw materials (coke and pitch) make it challenging to manufacture the anodes with consistent overall quality. Intercepting faulty anodes (e.g., presence of cracks and pores) before they are set in reduction cells and deteriorate their performance is therefore important. This is a difficult task, even in modern and well-instrumented anode plants, because lab testing using core samples can only characterize a small proportion of the anode production due to the costly, time-consuming, and destructive nature of the analytical methods. In addition, these results are not necessarily representative of the whole anode block. The objective of this work is to develop a rapid and non-destructive method for quality control of baked anodes using acousto-ultrasonic (AU) techniques. The acoustic responses of anode samples (sliced sections) were analyzed using a combination of temporal features computed from AU signals and principal component analysis (PCA). The AU signals were found sensitive to pores and cracks and were able to discriminate the two types of defects. The results were validated qualitatively by submitting the samples to X-ray Computed Tomography (CT scan). Full article

(This article belongs to the Special Issue Selected Papers from the International Committee for Study of Bauxite, Alumina&Aluminium 2015)

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4725 KiB

Open AccessArticle

Effects of Surface Structure and Chemical Composition of Binary Ti Alloys on Cell Differentiation

by Ok-Sung Han, Moon-Jin Hwang, Yo-Han Song, Ho-Jun Song and Yeong-Joon Park

Metals 2016, 6(7), 150; https://doi.org/10.3390/met6070150 - 04 Jul 2016

Cited by 2 | Viewed by 4136

Abstract

Binary Ti alloys containing Fe, Mo, V and Zr were micro-arc oxidized and hydrothermally treated to obtain micro- and nano-porous layers. This study aimed to investigate cell differentiation on micro and micro/nanoporous oxide layers of Ti alloys. The properties of the porous layer [...] Read more.

Binary Ti alloys containing Fe, Mo, V and Zr were micro-arc oxidized and hydrothermally treated to obtain micro- and nano-porous layers. This study aimed to investigate cell differentiation on micro and micro/nanoporous oxide layers of Ti alloys. The properties of the porous layer formed on Ti alloys were characterized by X-ray diffraction pattern, microstructural and elemental analyses and inductively coupled plasma mass spectrometry (ICP-MS) method. The MTT assay, total protein production and alkaline phosphatase (ALPase) activity were evaluated using human osteoblast-like cells (MG-63). Microporous structures of micro-arc oxidized Ti alloys were changed to micro/nanoporous surfaces after hydrothermal treatment. Micro/nanoporous surfaces consisted of acicular TiO₂ nanoparticles and micron-sized hydroxyapatite particles. From ICP and MTT tests, the Mo and V ions released from porous oxide layers were positive for cell viability, while the released Fe ions were negative for cell viability. Although the micro/nanoporous surfaces led to a lower total protein content than the polished and microporous Ti surfaces after cell incubation for 7 days, they caused higher ALPase activities after 7 days and 14 days of incubation except for V-containing microporous surfaces. The micro/nanoporous surfaces of Ti alloys were more efficient in inducing MG-63 cell differentiation. Full article

(This article belongs to the Special Issue Refractory Metals and Alloys)

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6088 KiB

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In Vitro Analysis of the Tribological Behaviour of Different Material Combinations for Telescopic Crowns

by Wigbert Linek, Gert Richter, Michael Raedel, Michael Walter and Bernd Reitemeier

Metals 2016, 6(7), 149; https://doi.org/10.3390/met6070149 - 30 Jun 2016

Cited by 1 | Viewed by 3376

Abstract

Telescopic crowns are used to connect removable dental prostheses with the remaining dentition. Several material combinations are used for manufacturing primary and secondary crowns. The present experimental study analysed the influence of different material combinations on the long-term development of surface roughness and [...] Read more.

Telescopic crowns are used to connect removable dental prostheses with the remaining dentition. Several material combinations are used for manufacturing primary and secondary crowns. The present experimental study analysed the influence of different material combinations on the long-term development of surface roughness and pull-off forces. Six different material combinations were tested. Secondary crowns were manufactured either by casting or electroforming. Each material combination was tested with n = 10 specimens. A material testing device with integrated power sensors was used for 10,000 cycles per test. Signs of wear were identified by surface roughness measurements, and visualized by a scanning electron microscope (SEM) and X-ray spectroscopy (EDX) technologies. Statistical significances were tested by using the U-Test with Bonferroni correction. The choice of materials and the manufacturing process were found to influence the long-term development of pull-off forces as well as wear-associated surface roughness. Combinations of different groups of materials for primary and secondary crowns showed favourable results. Worse results were found for the combination pure titanium and pure titanium and the combination high gold alloy and electroformed gold. Wear-associated surface roughness was higher for combinations of similar or identical groups of materials. For manufacturing telescopic crowns, combinations of different groups of materials are preferred. For secondary crown manufacturing, electroforming is superior to casting. Full article

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22527 KiB

Open AccessFeature PaperArticle

Corrosion Behavior of AlSi10Mg Alloy Produced by Additive Manufacturing (AM) vs. Its Counterpart Gravity Cast Alloy

by Avi Leon, Amnon Shirizly and Eli Aghion

Metals 2016, 6(7), 148; https://doi.org/10.3390/met6070148 - 30 Jun 2016

Cited by 85 | Viewed by 13239

Abstract

The attractiveness of additive manufacturing (AM) relates to the ability of this technology to rapidly produce very complex components at affordable costs. However, the properties and corrosion behavior, in particular, of products produced by AM technology should at least match the properties obtained [...] Read more.

The attractiveness of additive manufacturing (AM) relates to the ability of this technology to rapidly produce very complex components at affordable costs. However, the properties and corrosion behavior, in particular, of products produced by AM technology should at least match the properties obtained by conventional technologies. The present study aims at evaluating the corrosion behavior and corrosion fatigue endurance of AlSi10Mg alloy produced by selective laser melting (SLM) in comparison with its conventional counterpart, gravity cast alloy. The results obtained indicate that the corrosion resistance of the printed and cast alloys was relatively similar, with a minor advantage to the printed alloy. The corrosion fatigue endurance of the printed alloy was relatively improved compared to the cast alloy. This was mainly attributed to the significant differences between the microstructure and defect characteristics of those two alloys. Full article

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Effects of Cl Addition to Sb-Doped Perovskite-Type CH₃NH₃PbI₃ Photovoltaic Devices

by Takeo Oku, Yuya Ohishi, Atsushi Suzuki and Yuzuru Miyazawa

Metals 2016, 6(7), 147; https://doi.org/10.3390/met6070147 - 29 Jun 2016

Cited by 39 | Viewed by 6681

Abstract

The effects of SbI₃, PbCl₂, and NH₄Cl addition to perovskite CH₃NH₃PbI₃ precursor solutions on photovoltaic properties were investigated. TiO₂/CH₃NH₃Pb(Sb)I₃(Cl)-based photovoltaic devices were fabricated by [...] Read more.

The effects of SbI₃, PbCl₂, and NH₄Cl addition to perovskite CH₃NH₃PbI₃ precursor solutions on photovoltaic properties were investigated. TiO₂/CH₃NH₃Pb(Sb)I₃(Cl)-based photovoltaic devices were fabricated by a spin-coating technique, and the microstructures of the devices were investigated by X-ray diffraction and scanning electron microscopy. Current density-voltage characteristics and incident photon-to-current conversion efficiencies were improved by a small amount of Sb- and Cl-doping, which resulted in improvement of the efficiencies of the devices. The structure analysis indicated formation of a homogeneous microstructure by NH₄Cl addition with SbI₃. Full article

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1709 KiB

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Creep Aging Behavior Characterization of 2219 Aluminum Alloy

by Lingfeng Liu, Lihua Zhan and Wenke Li

Metals 2016, 6(7), 146; https://doi.org/10.3390/met6070146 - 29 Jun 2016

Cited by 6 | Viewed by 8001

Abstract

In order to characterize the creep behaviors of 2219 aluminum alloy at different temperatures and stress levels, a RWS-50 Electronic Creep Testing Machine (Zhuhai SUST Electrical Equipment Company, Zhuhai, China) was used for creep experiment at temperatures of 353~458 k and experimental stresses [...] Read more.

In order to characterize the creep behaviors of 2219 aluminum alloy at different temperatures and stress levels, a RWS-50 Electronic Creep Testing Machine (Zhuhai SUST Electrical Equipment Company, Zhuhai, China) was used for creep experiment at temperatures of 353~458 k and experimental stresses of 130~170 MPa. It was discovered that this alloy displayed classical creep curve characteristics in its creep behaviors within the experimental parameters, and its creep value increased with temperature and stress. Based on the creep equation of hyperbolic sine function, regression analysis was conducted of experimental data to calculate stress exponent, creep activation energy, and other related variables, and a 2219 aluminum alloy creep constitutive equation was established. Results of further analysis of the creep mechanism of the alloy at different temperatures indicated that the creep mechanism of 2219 aluminum alloy differed at different temperatures; and creek characteristics were presented in three stages at different temperatures, i.e., the grain boundary sliding creep mechanism at a low temperature stage (T < 373 K), the dislocation glide creep mechanism at a medium temperature stage (373 K ≤ T < 418 K), and the dislocation climb creep mechanism at a high temperature stage (T ≥ 418 K). By comparative analysis of the fitting results and experiment data, they were found to be in agreement with the experimental data, revealing that the established creep constitutive equation is suitable for different temperatures and stresses. Full article

(This article belongs to the Special Issue Aluminum Alloys)

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1366 KiB

Open AccessArticle

Synthesis and Characterization of Nanocrystalline Al-20 at. % Cu Powders Produced by Mechanical Alloying

by Molka Ben Makhlouf, Tarek Bachaga, Joan Josep Sunol, Mohamed Dammak and Mohamed Khitouni

Metals 2016, 6(7), 145; https://doi.org/10.3390/met6070145 - 29 Jun 2016

Cited by 21 | Viewed by 5319

Abstract

Mechanical alloying is a powder processing technique used to process materials farther from equilibrium state. This technique is mainly used to process difficult-to-alloy materials in which the solid solubility is limited and to process materials where nonequilibrium phases cannot be produced at room [...] Read more.

Mechanical alloying is a powder processing technique used to process materials farther from equilibrium state. This technique is mainly used to process difficult-to-alloy materials in which the solid solubility is limited and to process materials where nonequilibrium phases cannot be produced at room temperature through conventional processing techniques. This work deals with the microstructural properties of the Al-20 at. % Cu alloy prepared by high-energy ball milling of elemental aluminum and copper powders. The ball milling of powders was carried out in a planetary mill in order to obtain a nanostructured Al-20 at. % Cu alloy. The obtained powders were characterized using scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and X-ray diffraction (XRD). The structural modifications at different stages of the ball milling are investigated with X-ray diffraction. Several microstructure parameters such as the crystallite sizes, microstrains and lattice parameters are determined. Full article

(This article belongs to the Special Issue Aluminum Alloys)

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5993 KiB

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Examination of Solubility Models for the Determination of Transition Metals within Liquid Alkali Metals

by Jeremy Isler and Jinsuo Zhang

Metals 2016, 6(7), 144; https://doi.org/10.3390/met6070144 - 28 Jun 2016

Cited by 4 | Viewed by 5458

Abstract

The experimental solubility of transition metals in liquid alkali metal was compared to the modeled solubility calculated using various equations for solubility. These equations were modeled using the enthalpy calculations of the semi-empirical Miedema model and various entropy calculations. The accuracy of the [...] Read more.

The experimental solubility of transition metals in liquid alkali metal was compared to the modeled solubility calculated using various equations for solubility. These equations were modeled using the enthalpy calculations of the semi-empirical Miedema model and various entropy calculations. The accuracy of the predicted solubility compared to the experimental data is more dependent on which liquid alkali metal is being examined rather than the transition metal solute examined. For liquid lithium the calculated solubility by the model was generally larger than experimental values, while for liquid cesium the modeling solubility was significantly smaller than the experimental values. For liquid sodium, potassium, and rubidium the experimental solubilities were within the range calculated by this study. Few data approached the predicted temperature dependence of solubility and instead most data exhibited a less pronounced temperature dependence. Full article

(This article belongs to the Special Issue Process-Structure-Property Relationships in Metals)

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7490 KiB

Open AccessReview

Microwave Rapid Sintering of Al-Metal Matrix Composites: A Review on the Effect of Reinforcements, Microstructure and Mechanical Properties

by Penchal Reddy Matli, Rana Abdul Shakoor, Adel Mohamed Amer Mohamed and Manoj Gupta

Metals 2016, 6(7), 143; https://doi.org/10.3390/met6070143 - 25 Jun 2016

Cited by 47 | Viewed by 9559

Abstract

Aluminum metal matrix composites (AMMCs) are light-weight materials having wide-spread use in the automobile and aerospace industries due to their attractive physical and mechanical properties. The promising mechanical properties of AMMCs are ascribed to the size and distribution of the reinforcement, as well [...] Read more.

Aluminum metal matrix composites (AMMCs) are light-weight materials having wide-spread use in the automobile and aerospace industries due to their attractive physical and mechanical properties. The promising mechanical properties of AMMCs are ascribed to the size and distribution of the reinforcement, as well as to the grain size of the matrix. Microwave rapid sintering involves internal heating of aluminum compacts by passing microwave energy through them. The main features of the microwave sintering technique are a short processing time and a low energy consumption. The aim of this review article is to briefly present the microwave rapid sintering process and to summarize the recent published work on the sintering and properties of pure Al and Al-based matrix composites containing different reinforcements. Full article

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