Metals

16 pages, 3453 KiB

Open AccessArticle

Solvent Extraction and Separation of Nd, Pr and Dy from Leach Liquor of Waste NdFeB Magnet Using the Nitrate Form of Mextral® 336At in the Presence of Aquo-Complexing Agent EDTA

by Aarti Kumari, Kamala Kanta Sahu and Sushanta Kumar Sahu

Metals 2019, 9(2), 269; https://doi.org/10.3390/met9020269 - 25 Feb 2019

Cited by 30 | Viewed by 6630

Abstract

Solvent extraction and separation of Pr, Nd and Dy from a synthetic leach solution of spent NdFeB magnet from wind turbines in the presence of aquo-complexing agent Ethylenediaminetetraacetic acid (EDTA) was studied using the nitrate form of Mextral® 336At ([336At][NO₃]) as [...] Read more.

Solvent extraction and separation of Pr, Nd and Dy from a synthetic leach solution of spent NdFeB magnet from wind turbines in the presence of aquo-complexing agent Ethylenediaminetetraacetic acid (EDTA) was studied using the nitrate form of Mextral® 336At ([336At][NO₃]) as an extractant. The effect of different process parameters such as pH, extractant, nitrate, and EDTA concentrations on the extraction of Pr, Nd and Dy was studied. The extraction of these rare earths elements follows the order Pr > Nd > Dy, whereas EDTA forms stable complexes in the order Dy > Nd > Pr. The synergy of these two effects improved the selectivity among these elements as compared to when no aquo-complexing agent was used. The mechanism of extraction of rare earth elements was established by slope analysis method. The Fourier-Transform Infrared Spectroscopy (FTIR) spectra of [336At][NO₃] and extracted Nd complex were recorded to understand the interaction of extractant with rare earth metal ions in the organic phase. Full article

(This article belongs to the Special Issue Solvent Extraction of Critical Metals)

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15 pages, 25463 KiB

Open AccessArticle

Influence of Vanadium Microalloying on Deformation-Induced Pearlite Transformation of Eutectoid Steel

by Zhen Cai, Xinping Mao, Siqian Bao, Gang Zhao and Yaowen Xu

Metals 2019, 9(2), 268; https://doi.org/10.3390/met9020268 - 25 Feb 2019

Cited by 10 | Viewed by 4237

Abstract

In order to investigate the influence of vanadium microalloying on deformation-induced pearlite transformation (DIPT) of eutectoid steel, thermomechanical simulation tests were carried out in this study. The following four compositions of vanadium microalloying were applied in the tests: vanadium free in Steel A, [...] Read more.

In order to investigate the influence of vanadium microalloying on deformation-induced pearlite transformation (DIPT) of eutectoid steel, thermomechanical simulation tests were carried out in this study. The following four compositions of vanadium microalloying were applied in the tests: vanadium free in Steel A, vanadium content of 0.1 mass% in Steel B, vanadium content of 0.27 mass% in Steel C, and vanadium content of 0.1 mass% with the addition of 0.02 mass% N in Steel D. The dissolution of vanadium and precipitation of vanadium carbides, nitrides, or carbonitrides and the effect of vanadium microalloying on the fraction and morphology of deformation-induced pearlite for different magnitudes of strain were examined, and the mechanism of the effect was elucidated. The results revealed that DIPT could be significantly improved by vanadium microalloying with the addition of N but decreased and postponed without the addition of N because vanadium nitrides or carbonitrides were precipitated in austenite under a small strain and facilitated the nucleation of pearlite both along the boundary of austenite grain (AG pearlite) and intragranular (IG pearlite). Moreover, transformation kinetics of DIPT was fitted and compared. The results further revealed that the rate of DIPT in vanadium-microalloyed steel with the addition of N was twice as fast as that in the vanadium-free steel. In order to ensure the complete spheroidization of lamellar cementites in vanadium-microalloyed steel, a comparison of the morphology of cementites revealed that a greater magnitude of strain was required. Full article

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16 pages, 46011 KiB

Open AccessArticle

Microstructure and Mechanical Properties of TiC-Reinforced 316L Stainless Steel Composites Fabricated Using Selective Laser Melting

by Zhanyong Zhao, Jing Li, Peikang Bai, Hongqiao Qu, Minjie Liang, Haihong Liao, Liyun Wu, Pengchen Huo, Hu Liu and Jiaoxia Zhang

Metals 2019, 9(2), 267; https://doi.org/10.3390/met9020267 - 25 Feb 2019

Cited by 86 | Viewed by 7062

Abstract

TiC/316L stainless steel (316Lss) metal matrix composite parts have been formed using selective laser melting (SLM). In this study, we have investigated the influence of the TiC mass fraction on the microstructure evolution, microhardness, friction properties, wear properties, and corrosion resistance of the [...] Read more.

TiC/316L stainless steel (316Lss) metal matrix composite parts have been formed using selective laser melting (SLM). In this study, we have investigated the influence of the TiC mass fraction on the microstructure evolution, microhardness, friction properties, wear properties, and corrosion resistance of the TiC/316Lss composites. The results show that the microhardness increased by the addition of the TiC mass fraction. In terms of friction and wear properties, the corrosion resistance initially increased, and then decreased. Compared with the pure 316Lss (298.3 HV0.2), the microhardness of the TiC/316Lss composites, which were formed with 2 wt% TiC, was raised to 335.2 HV0.2, which was a 12.4% increase, while the average friction coefficient was 0.123. The reason for this is that the addition of TiC can effectively refine the cell size, and as the TiC content increases, the refinement effect is more obvious. During the melting process, TiC particles act as nucleation centres, hindering the growth of crystal cells, promoting the formation of the austenite phase, and forming fine equiaxed structures, which increases the strength. However, excessive TiC particles aggravate the spheroidisation during the process of SLM, leading to increased defects, as well as a decrease in density and corrosion resistance. Full article

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9 pages, 4516 KiB

Open AccessArticle

Effects of Heating Rate on Formation of Globular and Acicular Austenite during Reversion from Martensite

by Xianguang Zhang, Goro Miyamoto, Yuki Toji and Tadashi Furuhara

Metals 2019, 9(2), 266; https://doi.org/10.3390/met9020266 - 24 Feb 2019

Cited by 18 | Viewed by 4141

Abstract

The effects of heating rate on the formation of acicular and globular austenite during reversion from martensite in Fe–2Mn–1.5Si–0.3C alloy have been investigated. It was found that a low heating rate enhanced the formation of acicular austenite, while a high heating rate favored [...] Read more.

The effects of heating rate on the formation of acicular and globular austenite during reversion from martensite in Fe–2Mn–1.5Si–0.3C alloy have been investigated. It was found that a low heating rate enhanced the formation of acicular austenite, while a high heating rate favored the formation of globular austenite. The growth of acicular γ was accompanied by the partitioning of Mn and Si, while the growth of globular γ was partitionless. DICTRA simulation revealed that there was a transition in growth mode from partitioning to partitionless for the globular austenite with an increase in temperature at high heating rate. High heating rates promoted a reversion that occurred at high temperatures, which made the partitionless growth of globular austenite occur more easily. On the other hand, the severer Mn enrichment into austenite at low heating rate caused Mn depletion in the martensite matrix, which decelerated the reversion kinetics in the later stage and suppressed the formation of globular austenite. Full article

(This article belongs to the Special Issue TRIP Steels)

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13 pages, 4277 KiB

Open AccessArticle

Mineralogical Characteristics and Isothermal Oxidation Kinetics of Ironsand Pellets

by Yaozu Wang, Jianliang Zhang and Zhengjian Liu

Metals 2019, 9(2), 265; https://doi.org/10.3390/met9020265 - 23 Feb 2019

Cited by 15 | Viewed by 2991

Abstract

An in-depth understanding of mineralogical characteristics and the oxidation behaviors of ironsand is of great significance to make the best of ironsand and develop Ti-containing pellets. This paper quantitatively characterized the mineralogical characteristics of the ironsand from East Java in Indonesia through X-ray [...] Read more.

An in-depth understanding of mineralogical characteristics and the oxidation behaviors of ironsand is of great significance to make the best of ironsand and develop Ti-containing pellets. This paper quantitatively characterized the mineralogical characteristics of the ironsand from East Java in Indonesia through X-ray diffraction (XRD-Rietveld) and scanning electron microscope (SEM-EDS). The results indicated that the mineral composition of the ironsand was magnetite (22.7%), titanomagnetite (40.9%), enstatite (17.1%), hematite–ilmenite solid solution (14.5%), and magnesium iron aluminum silicon oxide (5.8%). The microstructure characterization of pellets after oxidation showed that the porosity of the pellets decreased from 20.7% to 11.7% with temperatures ranging from 1073 to 1473 K. Moreover, the activation energies of ironsand pellets were calculated by using model-function method. The calculated data of different mechanism functions indicated that the chemical reaction mechanism for the early stage of the oxidation fit A2 (random nucleation and nuclei growth) well, the chemical reaction mechanism for the post-oxidation at 1073–1273 K fit F1 (chemical reaction) well, and the chemical reaction mechanism for the post-oxidation at 1373 and 1473 K fit D4 (diffusion) well. The reaction mechanism and the limited link was finally discussed based on the kinetic analysis and the mineralogical characteristics. Full article

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12 pages, 7389 KiB

Open AccessArticle

Porosity and Microstructure Iron-Based Graded Materials Sintered by Spark Plasma Sintering and the Conventional Method

by Krzysztof Zarębski, Piotr Putyra and Dariusz Mierzwiński

Metals 2019, 9(2), 264; https://doi.org/10.3390/met9020264 - 23 Feb 2019

Cited by 2 | Viewed by 3161

Abstract

Using PNC-60 powder with the addition of graphite, cylindrical products characterized by different compositions of core and outer layers were made. Some compacts were sintered via the conventional process, while others were subjected to the spark plasma sintering method (SPS) at different times [...] Read more.

Using PNC-60 powder with the addition of graphite, cylindrical products characterized by different compositions of core and outer layers were made. Some compacts were sintered via the conventional process, while others were subjected to the spark plasma sintering method (SPS) at different times and temperatures. The gradient microstructure was obtained in the transition zone by mixing powders during die filling, followed by pressing and diffusion during sintering. The effect of sintering parameters on the nature of the gradient zone and the morphology of the pores was shown. After conventional sintering, the gradient zone was wider than it was after SPS. Via SPS, the short sintering time confined the diffusion to a local range, making its influence on the gradient structure negligible. Differences in the microstructure were confirmed by functional description. Full article

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10 pages, 3328 KiB

Open AccessArticle

Activation Volume and Energy for Dislocation Nucleation in Multi-Principal Element Alloys

by Sanghita Mridha, Maryam Sadeghilaridjani and Sundeep Mukherjee

Metals 2019, 9(2), 263; https://doi.org/10.3390/met9020263 - 23 Feb 2019

Cited by 45 | Viewed by 5575

Abstract

Incipient plasticity in multi-principal element alloys, CoCrNi, CoCrFeMnNi, and Al_0.1CoCrFeNi was evaluated by nano-indentation and compared with pure Ni. The tests were performed at a loading rate of 70 μN/s in the temperature range of 298 K to 473 K. The [...] Read more.

Incipient plasticity in multi-principal element alloys, CoCrNi, CoCrFeMnNi, and Al_0.1CoCrFeNi was evaluated by nano-indentation and compared with pure Ni. The tests were performed at a loading rate of 70 μN/s in the temperature range of 298 K to 473 K. The activation energy and activation volume were determined using a statistical approach of analyzing the “pop-in” load marking incipient plasticity. The CoCrFeMnNi and Al_0.1CoCrFeNi multi-principal element alloys showed two times higher activation volume and energy compared to CoCrNi and pure Ni, suggesting complex cooperative motion of atoms for deformation in the five component systems. The small calculated values of activation energy and activation volume indicate heterogeneous dislocation nucleation at point defects like vacancy and hot-spot. Full article

(This article belongs to the Special Issue Complex Concentrated Alloys (CCAs) - Current Understanding and Future Opportunities)

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12 pages, 3490 KiB

Open AccessArticle

First-Principles Calculation for the Influence of C and O on the Mechanical Properties of γ-TiAl Alloy at High Temperature

by Jiahua Wang, Yong Lu and Xiaohong Shao

Metals 2019, 9(2), 262; https://doi.org/10.3390/met9020262 - 22 Feb 2019

Cited by 6 | Viewed by 4052

Abstract

The elastic constants of temperature dependence, thermal expansion coefficient and phonon dispersion relations of γ-TiAl doped with C/O have been investigated using first-principles calculations in order to gain insight into the mechanical performance of γ-TiAl in cases of high temperature. This study shows [...] Read more.

The elastic constants of temperature dependence, thermal expansion coefficient and phonon dispersion relations of γ-TiAl doped with C/O have been investigated using first-principles calculations in order to gain insight into the mechanical performance of γ-TiAl in cases of high temperature. This study shows that γ-TiAl maintains stability at high temperatures introduced by C or O atoms. Importantly, the hardness increases and retains excellent resistance to external pressure. The results indicate that even if the TiAl alloy is doped with C or O atoms, it can also exhibit excellent mechanical properties at a high temperature. Full article

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13 pages, 4601 KiB

Open AccessArticle

Exploring the Correlation between Subsurface Residual Stresses and Manufacturing Parameters in Laser Powder Bed Fused Ti-6Al-4V

by Tatiana Mishurova, Katia Artzt, Jan Haubrich, Guillermo Requena and Giovanni Bruno

Metals 2019, 9(2), 261; https://doi.org/10.3390/met9020261 - 22 Feb 2019

Cited by 40 | Viewed by 4367

Abstract

Subsurface residual stresses (RS) were investigated in Ti-6Al-4V cuboid samples by means of X-ray synchrotron diffraction. The samples were manufactured by laser powder bed fusion (LPBF) applying different processing parameters, not commonly considered in open literature, in order to assess their influence on [...] Read more.

Subsurface residual stresses (RS) were investigated in Ti-6Al-4V cuboid samples by means of X-ray synchrotron diffraction. The samples were manufactured by laser powder bed fusion (LPBF) applying different processing parameters, not commonly considered in open literature, in order to assess their influence on RS state. While investigating the effect of process parameters used for the calculation of volumetric energy density (such as laser velocity, laser power and hatch distance), we observed that an increase of energy density led to a decrease of RS, although not to the same extent for every parameter variation. Additionally, the effect of support structure, sample roughness and LPBF machine effects potentially coming from Ar flow were studied. We observed no influence of support structure on subsurface RS while the orientation with respect to Ar flow showed to have an impact on RS. We conclude recommending monitoring such parameters to improve part reliability and reproducibility. Full article

(This article belongs to the Special Issue Advanced Characterization and On-Line Process Monitoring of Additively Manufactured Materials and Components)

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16 pages, 20270 KiB

Open AccessArticle

Burnishing of FSW Aluminum Al–Cu–Li Components

by Adrián Rodríguez, Amaia Calleja, Luis Norberto López de Lacalle, Octavio Pereira, Haizea González, Gorka Urbikain and Julien Laye

Metals 2019, 9(2), 260; https://doi.org/10.3390/met9020260 - 21 Feb 2019

Cited by 46 | Viewed by 4567

Abstract

Ball-burnishing is presented herein as a mechanical surface treatment for improving mechanical properties after the friction stir welding process. Ball-burnishing provides good surface finish, high compressive residual stresses, and a hardness increase of the surface layer. These characteristics are key for the fatigue [...] Read more.

Ball-burnishing is presented herein as a mechanical surface treatment for improving mechanical properties after the friction stir welding process. Ball-burnishing provides good surface finish, high compressive residual stresses, and a hardness increase of the surface layer. These characteristics are key for the fatigue life improvement of the component, and for wear resistance due to the higher hardness. This work presents a complete analysis of surface and sub-surface hardness values focusing on the determination of each process parameter influence. Burnishing pressure, radial width, and burnishing direction influence were analyzed. The tested material was 2050 aluminum alloy with two different heat treatments (T3 and T8). The optimum parameters were established, and a complete analysis of the surface hardness was performed. Results show that burnishing is an economical and feasible mechanical treatment for the quality improvement of component surfaces. Full article

(This article belongs to the Special Issue New Processes and Machine Tools for Advanced Metal Alloys)

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10 pages, 2087 KiB

Open AccessArticle

Molecular Simulations of Sputtering Preparation and Transformation of Surface Properties of Au/Cu Alloy Coatings Under Different Incident Energies

by Linxing Zhang, Sen Tian and Tiefeng Peng

Metals 2019, 9(2), 259; https://doi.org/10.3390/met9020259 - 21 Feb 2019

Cited by 19 | Viewed by 3633

Abstract

The surface properties of coatings during deposition are strongly influenced by temperature, particle fluxes, and compositions. In addition, the precursor incident energy also affects the surface properties of coatings during sputtering. The atomistic processes associated with the microstructure of coatings and the surface [...] Read more.

The surface properties of coatings during deposition are strongly influenced by temperature, particle fluxes, and compositions. In addition, the precursor incident energy also affects the surface properties of coatings during sputtering. The atomistic processes associated with the microstructure of coatings and the surface morphological evolution during sputtering are difficult to observe. Thus, in the present study, molecular dynamics simulation was employed to investigate the surface properties of Au/Cu alloy coatings (Cu substrate sputtering by Au atoms) with different incident energies (0.15 eV, 0.3 eV, 0.6 eV). Subsequently, the sputtering depth of the Au atoms, the particle distribution of the Au/Cu alloy coating system, the radial distribution function of particles in the coatings, the mean square displacement of the Cu atoms in the substrate, and the roughness of the coatings were analyzed. Results showed that the crystal structure and the sputtering depth of Au atoms were hardly influenced by the incident energy, and the incident energy had little impact on the motion of deep-lying atoms in the substrate. However, higher incident energy resulted in higher surface temperature of coatings, and more Au atoms existed in the coherent interface. Moreover, it strengthened the motion of Cu atoms and reduced the surface roughness. Therefore, the crystal structure of coatings and the motions of deep-lying atoms in the substrate are not influenced by the incident energy. However, the increase in incident energy will enhance the combination of coatings and the base while optimizing the surface structure. Full article

(This article belongs to the Special Issue Synthesis and Properties of Metallic Multilayers)

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9 pages, 5386 KiB

Open AccessArticle

In Situ Observation of the Deformation and Fracture Behaviors of Long-Term Thermally Aged Cast Duplex Stainless Steels

by Shilei Li, Yanli Wang and Xitao Wang

Metals 2019, 9(2), 258; https://doi.org/10.3390/met9020258 - 21 Feb 2019

Cited by 10 | Viewed by 3340

Abstract

Cast duplex stainless steel (CDSS) components suffer embrittlement after long-term thermal aging. The deformation and fracture behaviors of un-aged and thermally aged (at 400 °C for 20,000 h) CDSS were investigated using in situ scanning electron microscopy (SEM). The tensile strength of CDSS [...] Read more.

Cast duplex stainless steel (CDSS) components suffer embrittlement after long-term thermal aging. The deformation and fracture behaviors of un-aged and thermally aged (at 400 °C for 20,000 h) CDSS were investigated using in situ scanning electron microscopy (SEM). The tensile strength of CDSS had a small increase, and the tensile fracture changed from ductile to brittle after thermal aging. Observations using in situ SEM indicated that the initial cracks appeared in the ferrite perpendicular to the loading direction after the macroscopic stress exceeded a critical value. The premature fracture of ferrite grains caused stress on the phase boundaries, leading the cracks to grow into austenite. The cleavage fracture of ferrite accelerated the shearing of austenite and reduced the plasticity of the thermally aged CDSS. Full article

(This article belongs to the Special Issue Failure Mechanisms in Alloys)

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11 pages, 4694 KiB

Open AccessArticle

Oxide-Inclusion Evolution in the Steelmaking Process of 304L Stainless Steel for Nuclear Power

by Xingrun Chen, Guoguang Cheng, Yuyang Hou and Jingyu Li

Metals 2019, 9(2), 257; https://doi.org/10.3390/met9020257 - 21 Feb 2019

Cited by 6 | Viewed by 5268

Abstract

The inclusions formed in 304L stainless steel for nuclear power produced by the electric arc furnace (EAF)-argon oxygen decarburization furnace (AOD)-ladle furnace (LF)-continuous casting (CC) process were investigated by thermodynamics calculations and experimental results. The results showed that the inclusions after AOD and [...] Read more.

The inclusions formed in 304L stainless steel for nuclear power produced by the electric arc furnace (EAF)-argon oxygen decarburization furnace (AOD)-ladle furnace (LF)-continuous casting (CC) process were investigated by thermodynamics calculations and experimental results. The results showed that the inclusions after AOD and LF refining were almost the same as the slag composition. The types of inclusions (sizes larger than 5 µm) were mainly CaSiO₃ with high SiO₂ content at the end of AOD, and Ca₂SiO₄ with high CaO content at the end of LF. The Al₂O₃ and MgO content of inclusions increased from AOD to LF. There were two types of inclusions in the tundish: CaO-SiO₂-Al₂O₃-MgO and CaO-SiO₂-Al₂O₃-MgO-MnO inclusions with MgO·Al₂O₃ spinel precipitation. The content of Al₂O₃ in the inclusions increased rapidly with the decrease in temperature from the end of LF refining to continuous casting, as calculated using FactSage6.3 software. The rapid increase of Al₂O₃ in the CaO-SiO₂-Al₂O₃-MgO-(MnO) inclusions promoted the precipitation of MgO·Al₂O₃ spinel in continuous casting tundish, suggesting mechanisms for the formation of inclusions in the 304L stainless steel. Full article

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17 pages, 4070 KiB

Open AccessArticle

Microstructural Characterization and Mechanical Properties of Direct Quenched and Partitioned High-Aluminum and High-Silicon Steels

by Pekka Kantanen, Mahesh Somani, Antti Kaijalainen, Oskari Haiko, David Porter and Jukka Kömi

Metals 2019, 9(2), 256; https://doi.org/10.3390/met9020256 - 21 Feb 2019

Cited by 24 | Viewed by 4311

Abstract

A new experimental steel containing in weight percent 0.3C-2.0Mn-0.5Si-1.0Al-2.2Cr and 0.3C-1.9Mn-1.0Si-1.0Cr was hot rolled in a laboratory rolling mill and directly quenched within the martensite start and finish temperature range. It was then partitioned without reheating during slow furnace cooling to achieve tensile [...] Read more.

A new experimental steel containing in weight percent 0.3C-2.0Mn-0.5Si-1.0Al-2.2Cr and 0.3C-1.9Mn-1.0Si-1.0Cr was hot rolled in a laboratory rolling mill and directly quenched within the martensite start and finish temperature range. It was then partitioned without reheating during slow furnace cooling to achieve tensile yield strengths over 1100 MPa with good combinations of strength, ductility and impact toughness. Gleeble thermomechanical simulations led to the selection of the partitioning at the temperatures 175 and 225 °C, which produced the desired microstructures of lath martensite with finely divided retained austenite in fractions of 6.5% and 10% respectively. The microstructures were analyzed using light and scanning electron microscopy in combination with electron backscatter diffraction and X-ray diffraction analysis. The mechanical properties were characterized extensively using hardness, tensile and Charpy V impact testing. In tensile testing a transformation induced plasticity mechanism was shown to operate with the less stable, carbon-poorer retained austenite, which transformed to martensite during straining. The auspicious results in respect to microstructures and mechanical properties indicate that there are possibilities for developing tough ductile structural steels through thermomechanical rolling followed by the direct quenching and partitioning route. Full article

(This article belongs to the Special Issue Advanced High Strength Steels by Quenching and Partitioning)

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10 pages, 1049 KiB

Open AccessArticle

Multiaxial Fatigue Life Prediction of GH4169 Alloy Based on the Critical Plane Method

by Jianhui Liu, Zhen Zhang, Bin Li and Shanshan Lang

Metals 2019, 9(2), 255; https://doi.org/10.3390/met9020255 - 20 Feb 2019

Cited by 17 | Viewed by 3752

Abstract

The multiaxial fatigue life of GH4169 alloy was predicted based on the critical plane method. In this paper, a new critical plane-damage multiaxial fatigue parameter is proposed, in which the maximum shear strain is considered to be the main damage control parameter, and [...] Read more.

The multiaxial fatigue life of GH4169 alloy was predicted based on the critical plane method. In this paper, a new critical plane-damage multiaxial fatigue parameter is proposed, in which the maximum shear strain is considered to be the main damage control parameter, and the correction parameter, including the normal stress and strain of the maximum shear strain plane, is defined as the second control parameter. The axis of principle strain rotates under non-proportional loading. Meanwhile, the mechanism of the variation of material microstructure and slip systems leads to an additional hardening phenomenon. The ratio of cyclic yield stress to static yield stress is used to represent cyclic strengthening capacity, and the influence of the phase difference and loading condition on the non-proportional reinforcement effect is considered. It is also proposed that different materials have different influences on the additional hardening phenomenon. Meanwhile, the model revision results in stress under asymmetrical loading. Experimental data of GH4169 alloy show that the proposed model can provide better prediction than the Smith–Watson–Topper (SWT) and Fatemi–Socie (FS) models. Full article

(This article belongs to the Special Issue Metal Fracture Modeling)

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23 pages, 5216 KiB

Open AccessReview

A Review of Multi-Scale Computational Modeling Tools for Predicting Structures and Properties of Multi-Principal Element Alloys

by Mohsen Beyramali Kivy, Yu Hong and Mohsen Asle Zaeem

Metals 2019, 9(2), 254; https://doi.org/10.3390/met9020254 - 20 Feb 2019

Cited by 14 | Viewed by 6988

Abstract

Multi-principal element (MPE) alloys can be designed to have outstanding properties for a variety of applications. However, because of the compositional and phase complexity of these alloys, the experimental efforts in this area have often utilized trial and error tests. Consequently, computational modeling [...] Read more.

Multi-principal element (MPE) alloys can be designed to have outstanding properties for a variety of applications. However, because of the compositional and phase complexity of these alloys, the experimental efforts in this area have often utilized trial and error tests. Consequently, computational modeling and simulations have emerged as power tools to accelerate the study and design of MPE alloys while decreasing the experimental costs. In this article, various computational modeling tools (such as density functional theory calculations and atomistic simulations) used to study the nano/microstructures and properties (such as mechanical and magnetic properties) of MPE alloys are reviewed. The advantages and limitations of these computational tools are also discussed. This study aims to assist the researchers to identify the capabilities of the state-of-the-art computational modeling and simulations for MPE alloy research. Full article

(This article belongs to the Special Issue Complex Concentrated Alloys (CCAs) - Current Understanding and Future Opportunities)

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12 pages, 4916 KiB

Open AccessFeature PaperArticle

Inclusions Control and Refining Slag Optimization for Fork Flat Steel

by Yangyang Ge, Shuo Zhao, Liang Ma, Tao Yan, Zushu Li and Bin Yang

Metals 2019, 9(2), 253; https://doi.org/10.3390/met9020253 - 20 Feb 2019

Cited by 6 | Viewed by 3540

Abstract

In order to investigate the causes of the large number of cracks and porosities formed in 33MnCrTiB fork flat steel produced by a special steel plant, scanning electron microscopy (SEM), energy dispersive spectrometer (EDS) analysis, and large sample electrolysis of the obtained steel [...] Read more.

In order to investigate the causes of the large number of cracks and porosities formed in 33MnCrTiB fork flat steel produced by a special steel plant, scanning electron microscopy (SEM), energy dispersive spectrometer (EDS) analysis, and large sample electrolysis of the obtained steel samples were carried out in different steps of the steelmaking processes. The main micro-inclusions in the fork flat steel samples were Al₂O₃, CaO-MgO-Al₂O₃-SiO₂, and TiN, and the macro-inclusions were mainly Al₂O₃, CaO-Al₂O₃, CaO-Al₂O₃-SiO₂-TiO₂, and CaO-MgO-Al₂O₃-SiO₂-TiO₂-(K₂O) systems which originated from the ladle slag and mold flux in the production process. In order to reduce the number of micro-inclusions effectively, the control range of components in the refining slag was confirmed by the thermodynamic calculation, where the mass ratio of CaO/Al₂O₃ should be in the range of 1.85–1.92, and the mass fraction of SiO₂ and MgO should be controlled to 7.5–20% and 6–8%, respectively. In addition, the numbers of macro-inclusions in the flat steel should be effectively reduced by optimizing the flow field of mold and preventing the secondary oxidation, and the flat steel quality problems caused by the inclusions can be improved by the optimization process above. Full article

(This article belongs to the Special Issue Ironmaking and Steelmaking)

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14 pages, 1026 KiB

Open AccessArticle

Electronic Structure Calculations of Oxygen Atom Transport Energetics in the Presence of Screw Dislocations in Tungsten

by Yue Zhao, Lucile Dezerald and Jaime Marian

Metals 2019, 9(2), 252; https://doi.org/10.3390/met9020252 - 20 Feb 2019

Cited by 18 | Viewed by 4991

Abstract

Plastic flow in body-centered cubic (bcc) alloys is governed by the thermally-activated motion of screw dislocations in close-packed planes. In bcc interstitial solid solutions, solute diffusion can occur at very fast rates owing to low migration energies and solute concentrations. Under mechanical loading, [...] Read more.

Plastic flow in body-centered cubic (bcc) alloys is governed by the thermally-activated motion of screw dislocations in close-packed planes. In bcc interstitial solid solutions, solute diffusion can occur at very fast rates owing to low migration energies and solute concentrations. Under mechanical loading, solutes may move on the same or similar time scale as dislocations glide, even at low temperatures, potentially resulting in very rich co-evolution processes that may have important effects in the overall material response. It is therefore important to accurately quantify the coupling between interstitial impurities and dislocations, so that larger-scale models can correctly account for their interactions. In this paper, we use electronic structure calculations to obtain the energetics of oxygen diffusion under stress and its interaction energy with screw dislocation cores in bcc tungsten. We find that oxygen atoms preferentially migrate from tetrahedral to tetrahedral site with an energy of 0.2 eV. This energy couples only weakly to hydrostatic and deviatoric deformations, with activation volumes of less than

0.02

and

0.02 b^{3}

, respectively. The strongest effect is found for the inelastic interaction between O atoms and screw dislocation cores, which leads to attractive energies between 1.2 and 1.9 eV and sometimes triggers a transformation of the screw dislocation core from an easy core configuration to a hard core configuration. Full article

(This article belongs to the Special Issue Advanced Tungsten Materials)

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9 pages, 1902 KiB

Open AccessArticle

Desiliconisation and Dephosphorisation Behaviours of Various Oxygen Sources in Hot Metal Pre-Treatment

by Youngjo Kang

Metals 2019, 9(2), 251; https://doi.org/10.3390/met9020251 - 20 Feb 2019

Cited by 6 | Viewed by 4113

Abstract

In order to obtain a better understanding of the efficiencies of desiliconisation and dephosphorisation reactions during hot metal pretreatment in an open ladle, a number of simulation experiments were carried out with various oxygen sources. Three types of solid oxygen materials (sintered return [...] Read more.

In order to obtain a better understanding of the efficiencies of desiliconisation and dephosphorisation reactions during hot metal pretreatment in an open ladle, a number of simulation experiments were carried out with various oxygen sources. Three types of solid oxygen materials (sintered return ore, scale briquette and fine mill scale) were carefully investigated as hot metal pre-treatment agents, evaluating their desiliconisation and dephosphorisation efficiencies. The method applied for supplying gaseous oxygen was also assessed. The comparison between top blowing and injection methods indicated that injected oxygen gas is more advantageous for desiliconisation, while top-blown oxygen gas is favourable for dephosphorisation. The obtained information on the characteristics of gaseous oxygen can be used for the optimisation of blowing patterns, in order to improve the efficiency of the hot metal pre-treatment. Full article

(This article belongs to the Special Issue Ironmaking and Steelmaking)

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16 pages, 5537 KiB

Open AccessArticle

Microstructure-Based Constitutive Modelling of Low-Alloy Multiphase TRIP Steels

by Álvaro Salinas, Diego Celentano, Linton Carvajal, Alfredo Artigas and Alberto Monsalve

Metals 2019, 9(2), 250; https://doi.org/10.3390/met9020250 - 20 Feb 2019

Cited by 7 | Viewed by 4144

Abstract

The microstructure of low-alloy multiphase transformation-induced plasticity (TRIP) steels consists of ferrite, bainite, and metastable retained austenite, which can be transformed into martensite by plastic deformation. In some cases, residual martensite can be present in the initial microstructure. The mechanical behavior of these [...] Read more.

The microstructure of low-alloy multiphase transformation-induced plasticity (TRIP) steels consists of ferrite, bainite, and metastable retained austenite, which can be transformed into martensite by plastic deformation. In some cases, residual martensite can be present in the initial microstructure. The mechanical behavior of these steels depends on the interaction between the intrinsic characteristics of the existing phases and the austenite stability. Due to these factors, the definition of their true stress-strain flow law is complex. This work presents the mechanical characterization of a phenomenological constitutive stress-strain flow law based on the Bouquerel et al. model, as evaluated for three TRIP steels of the same composition but undergoing different heat treatments. Morphological aspects of the existing phases, austenite stability, and suitable mixture laws between phases are considered. The model is found to accurately reproduce a true stress-strain flow law obtained under tensile uniaxial conditions and provide detailed information on the effective stress strain partition between the existing phases. Full article

(This article belongs to the Special Issue Constitutive Modelling for Metals)

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13 pages, 15327 KiB

Open AccessArticle

Thermal Simulation Study on the Solidification Structure and Segregation of a Heavy Heat-Resistant Steel Casting

by Biao Wang, Honggang Zhong, Xihao Li, Xiebin Wang, Tieming Wu, Qingmei Liu and Qijie Zhai

Metals 2019, 9(2), 249; https://doi.org/10.3390/met9020249 - 20 Feb 2019

Cited by 8 | Viewed by 3447

Abstract

The prediction and controlling of the solidification structure and macro-segregation in heavy steel casting, which is usually produced in limited quantities, was a conundrum in the foundry field. In this work, the cooling and solidification processes of a 16 t CB2 ferritic heat-resistant [...] Read more.

The prediction and controlling of the solidification structure and macro-segregation in heavy steel casting, which is usually produced in limited quantities, was a conundrum in the foundry field. In this work, the cooling and solidification processes of a 16 t CB2 ferritic heat-resistant steel (FHRS) valve casting were reproduced by studying the solidification behavior of three typical units through a thermal simulation method. The results indicate that the types of casting without chilling have the most uneven distribution of solutes and hardness, while those types of casting in which parts are solidified by chilling are much more uniform. The macro-segregation degrees of B, C, Nb, P, Cr, Mo, Si, V and Mn decrease gradually during heavy casting of CB2 ferritic heat-resistant steel. Of them, B, C, Nb, and P are solutes prone to segregation, and the maximum macro-segregation index of B can even reach 15. The macro-segregation tendencies of Cr, Mo, Si, V, and Mn are relatively small. Further studies on the last solidification portion of samples taken by electron microprobe reveal that large-sized precipitates such as MnS and Nb_xC are easily formed due to solute enrichment, and the sizes of these precipitates were distributed from dozens to hundreds of micrometers. Full article

(This article belongs to the Special Issue Advanced Simulation Technologies of Metallurgical Processing)

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12 pages, 4020 KiB

Open AccessArticle

Properties of Jet-Plated Ni Coating on Ti Alloy (Ti6Al4V) with Laser Cleaning Pretreatment

by Xiao Wang, Mingyang Xu, Zhanwen Wang, Lida Shen, Mingbo Qiu, Zongjun Tian, Muhammad Naveed Ahsan and Changjiang Wang

Metals 2019, 9(2), 248; https://doi.org/10.3390/met9020248 - 20 Feb 2019

Cited by 10 | Viewed by 3615

Abstract

The surface mechanical properties of the Selective Laser Melting (SLM) formed Ti6Al4V samples were improved by adopting a novel laser cleaning pretreatment process combined with a jet electrodeposition process. This paper aimed to investigate the effects of different laser powers on the morphologies [...] Read more.

The surface mechanical properties of the Selective Laser Melting (SLM) formed Ti6Al4V samples were improved by adopting a novel laser cleaning pretreatment process combined with a jet electrodeposition process. This paper aimed to investigate the effects of different laser powers on the morphologies and adhesions of the nickel coatings. The advantages of the laser cleaning process are no grinding, no contact, high efficiency and environmental protection. The morphologies, adhesion, wear resistance, and hardness of the coatings were characterized. The results indicate that when the laser energy density reached 20% (4 J/cm²), the contaminations on the substrate and the oxide layer were removed and the crystalline grain of the coating was 15.3 nm. The shallow pits generated by laser burning increased the adhesion of the coatings. In addition, when the laser energy density increased to 6 J/cm², a yellow oxide layer was produced on the surface of the cleaned titanium alloy. Moreover, the wear resistance of the titanium alloy after the nickel plating was improved. The wear volume was only 0.046 mm³, and the hardness increased to 1967.6 N/mm². Full article

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18 pages, 1408 KiB

Open AccessArticle

Intermetallic Phases in High-Entropy Alloys: Statistical Analysis of their Prevalence and Structural Inheritance

by Ming-Hung Tsai, Ruei-Chi Tsai, Ting Chang and Wen-Fei Huang

Metals 2019, 9(2), 247; https://doi.org/10.3390/met9020247 - 19 Feb 2019

Cited by 62 | Viewed by 7000

Abstract

Strengthening high entropy alloys (HEAs) via second phases is a very effective approach. However, the design of intermetallic (IM) phases in HEAs is challenging, mainly because our understanding of IM phases in HEAs is still very limited. Here, a statistical approach is used [...] Read more.

Strengthening high entropy alloys (HEAs) via second phases is a very effective approach. However, the design of intermetallic (IM) phases in HEAs is challenging, mainly because our understanding of IM phases in HEAs is still very limited. Here, a statistical approach is used to enhance our understanding towards IM phases in HEAs. A database consisting of 142 IM-containing HEAs was constructed. Our aim is twofold. The first is to reveal the most common IM phase types in published HEAs. The second is to understand whether HEAs inherit their IM structures from their binary/ternary subsystems, or whether they tend to form new structures irrelevant to their subsystems. The results show that the five most prevalent IM structures in the HEAs surveyed here are Laves, σ, B2, L1₂, and L2₁. This trend is evidently different from the overall trend among known binary/ternary IMs. As for structural inheritance, all the IM phases contained in the alloys are existing structures in the binary/ternary subsystems of the respective alloys. This suggests that the compositional complexity in HEAs does trigger additional complexity in IM structure formation. These findings have important implications in the future design and development of HEAs. Full article

(This article belongs to the Special Issue High Entropy Materials: Challenges and Prospects)

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16 pages, 8919 KiB

Open AccessArticle

The Influence of the Post-Weld Heat Treatment on the Microstructure of Inconel 625/Carbon Steel Bimetal Joint Obtained by Explosive Welding

by Robert Kosturek, Marcin Wachowski, Lucjan Śnieżek and Michał Gloc

Metals 2019, 9(2), 246; https://doi.org/10.3390/met9020246 - 19 Feb 2019

Cited by 24 | Viewed by 5766

Abstract

Inconel 625 and steel P355NH were bonded by explosive welding in this study. Explosively welded bimetal clad-plate was subjected to the two separated post-weld heat treatment processes: stress relief annealing (at 620 °C for 90 min) and normalizing (at 910 °C for 30 [...] Read more.

Inconel 625 and steel P355NH were bonded by explosive welding in this study. Explosively welded bimetal clad-plate was subjected to the two separated post-weld heat treatment processes: stress relief annealing (at 620 °C for 90 min) and normalizing (at 910 °C for 30 min). Effect of heat treatments on the microstructure of the joint has been evaluated using light and scanning electron microscopy, EDS analysis techniques, and microhardness tests, respectively. It has been stated that stress relief annealing leads to partial recrystallization of steel P355NH microstructure in the joint zone. At the same time, normalizing caused not only the recrystallization of both materials, but also the formation of a diffusion zone and precipitates in Inconel 625. The precipitates in Inconel 625 have been identified as two types of carbides: chromium-rich M₂₃C₆ and molybdenum-rich M₆C. It has been reported that diffusion of alloying elements into steel P355NH takes place along grain boundaries with additional formation of voids. Scanning transmission electron microscope observation of the grain microstructure in the diffusion zone shows that this area consists of equiaxed grains (at the side of Inconel 625 alloy) and columnar grains (at the side of steel P355NH). Full article

(This article belongs to the Special Issue Explosive Welding)

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10 pages, 286 KiB

Open AccessFeature PaperArticle

Transient Effects in Creep of Sanicro 25 Austenitic Steel and Their Modelling

by Luboš Kloc, Václav Sklenička and Petr Dymáček

Metals 2019, 9(2), 245; https://doi.org/10.3390/met9020245 - 19 Feb 2019

Cited by 3 | Viewed by 3327

Abstract

Transient effects upon stress changes during creep of the new Sanicro 25 steel were investigated experimentally using the helicoid spring specimen technique. The creep behaviour was found to be qualitatively the same as that observed earlier with the creep-resistant 9% Cr ferritic-martensitic P-91 [...] Read more.

Transient effects upon stress changes during creep of the new Sanicro 25 steel were investigated experimentally using the helicoid spring specimen technique. The creep behaviour was found to be qualitatively the same as that observed earlier with the creep-resistant 9% Cr ferritic-martensitic P-91 steel, but the transient strains are considerably smaller. Negative creep rate, which is strain running against the applied stress, was observed with any stress decrease. Parameters for the complex creep model were estimated and model results were compared to the creep rates measured experimentally. The model can be used for the finite element method modelling of the creep and stress relaxation effects in the components made from the Sanicro 25 steel. Full article

(This article belongs to the Special Issue Metal Plasticity and Fatigue at High Temperature)

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12 pages, 6250 KiB

Open AccessArticle

Hardfacing Welded ASTM A572-Based, High-Strength, Low-Alloy Steel: Welding, Characterization, and Surface Properties Related to the Wear Resistance

by Nakarin Srisuwan, Nuengruetai Kumsri, Trinet Yingsamphancharoen and Attaphon Kaewvilai

Metals 2019, 9(2), 244; https://doi.org/10.3390/met9020244 - 19 Feb 2019

Cited by 18 | Viewed by 6272

Abstract

This work presents the improvement of hardfacing welding for American Society for Testing and Materials (ASTM) A572-based high-strength, low-alloy steel by controlling the heating/cooling conditions of welding process. In the welding process, the buffer and hardfacing layers were welded onto A572-based material by [...] Read more.

This work presents the improvement of hardfacing welding for American Society for Testing and Materials (ASTM) A572-based high-strength, low-alloy steel by controlling the heating/cooling conditions of welding process. In the welding process, the buffer and hardfacing layers were welded onto A572-based material by a nickel–chromium electrode and chromium carbide electrode, respectively. The base metal and electrode materials were controlled by the heating/cooling process during the welding to reduce excessive stress, which could result in a crack in the specimens. The welded specimens were examined by visual and penetrant inspections for evaluating the welding quality. The macro–micro structure of the deposited layer was investigated; scanning electron microscope with an energy-dispersive X-ray spectrometer (SEM-EDS) and XRD were used to characterize structural properties, elemental compositions, and crystallite sizes of the welded specimens. The surface properties, such as hardness, impact, and abrasive wear of the welded specimens, were tested for evaluation of the wear resistance of the welded specimens. Full article

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13 pages, 3002 KiB

Open AccessArticle

Hot Deformation Behavior of a 2024 Aluminum Alloy Sheet and its Modeling by Fields-Backofen Model Considering Strain Rate Evolution

by Zhubin He, Zhibiao Wang, Yanli Lin and Xiaobo Fan

Metals 2019, 9(2), 243; https://doi.org/10.3390/met9020243 - 18 Feb 2019

Cited by 16 | Viewed by 4417

Abstract

The deformation behavior of a 2024 aluminum alloy sheet at elevated temperatures was studied by uniaxial hot tensile tests over the nominal initial strain rate range of 0.001–0.1 s⁻¹ and temperature range of 375–450 °C. In order to analyze the deformation behavior [...] Read more.

The deformation behavior of a 2024 aluminum alloy sheet at elevated temperatures was studied by uniaxial hot tensile tests over the nominal initial strain rate range of 0.001–0.1 s⁻¹ and temperature range of 375–450 °C. In order to analyze the deformation behavior with higher accuracy, a digital image correlation (DIC) system was applied to determine the strain distribution during hot tensile tests. Local stress-strain curves for different local points on the specimens were calculated. The strain rate evolution of each point during the tensile tests was investigated under different deformation conditions. Then, an improved Fields–Backofen (FB) model, taking into account the local strain rate evolution instead of the fixed strain rate, was proposed to describe the constitutive behaviors. It has been found that obvious non-uniform strain distribution occurred when the true strain was larger than 0.3 during hot tensile tests. The strain rate distribution during deformation was also non-uniform. It showed increasing, steady, and decreasing variation tendencies for different points with the increasing of strain, which led to the local flow stress being different at different local points. The flow stresses predicted by the improved FB model showed good agreement with experimental results when the strain rate evolutions of local points during tensile tests were considered. The prediction accuracy was higher than that of traditional FB models. Full article

(This article belongs to the Special Issue Constitutive Modelling for Metals)

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9 pages, 2893 KiB

Open AccessFeature PaperArticle

First Hydrogenation Enhancement in TiFe Alloys for Hydrogen Storage Doped with Yttrium

by Catherine Gosselin and Jacques Huot

Metals 2019, 9(2), 242; https://doi.org/10.3390/met9020242 - 18 Feb 2019

Cited by 32 | Viewed by 4062

Abstract

The aim of this investigation was to improve the first hydrogenation of TiFe by adding yttrium. The compositions studied were TiFe + x wt.% Y with x = 4, 6, and 8. From electron microscopy it was found that all alloys were multiphase [...] Read more.

The aim of this investigation was to improve the first hydrogenation of TiFe by adding yttrium. The compositions studied were TiFe + x wt.% Y with x = 4, 6, and 8. From electron microscopy it was found that all alloys were multiphase with a matrix of TiFe phase containing less than 0.4 at.% of Y and a secondary phase rich in yttrium. When x increased, the chemical compositions of the matrix changed and the secondary phase changed. The sample with 8% of yttrium had the fastest kinetics. The hydrogen capacity increased with the amount of Y. Full article

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19 pages, 9653 KiB

Open AccessArticle

Sn-0.5Cu(-x)Al Solder Alloys: Microstructure-Related Aspects and Tensile Properties Responses

by Thiago Soares Lima, Guilherme Lisboa de Gouveia, Rudimylla da Silva Septimio, Clarissa Barros da Cruz, Bismarck Luiz Silva, Crystopher Brito, José Eduardo Spinelli and Noé Cheung

Metals 2019, 9(2), 241; https://doi.org/10.3390/met9020241 - 17 Feb 2019

Cited by 3 | Viewed by 4535

Abstract

In this study, experiments were conducted to analyze the effect of 0.05 and 0.1 wt.% Al additions during the unsteady-state growth of the Sn-0.5wt.%Cu solder alloy. Various as-solidified specimens of each alloy were selected so that tensile tests could also be performed. Microstructural [...] Read more.

In this study, experiments were conducted to analyze the effect of 0.05 and 0.1 wt.% Al additions during the unsteady-state growth of the Sn-0.5wt.%Cu solder alloy. Various as-solidified specimens of each alloy were selected so that tensile tests could also be performed. Microstructural aspects such as the dimensions of primary, λ₁, and secondary, λ₂, dendritic arrays, and intermetallic compounds (IMCs) morphologies were comparatively assessed for the three tested compositions, that is, Sn-0.5wt.%Cu, Sn-0.5wt.%Cu-0.05wt.%Al, and Sn-0.5wt.%Cu-0.1wt.%Al alloys. Al addition affected neither the primary dendritic spacing nor the types of morphologies identified for the Cu₆Sn₅ IMC, which was found to be either globular or fibrous regardless of the alloy considered. Secondary dendrite arm spacing was found to be enlarged and the eutectic fraction was reduced with an increase in the Al-content. Tensile properties remained unaffected with the addition of Al, except for the improvement in ductility of up to 40% when compared to the Sn-0.5wt.%Cu alloy without Al trace. A smaller λ₂ in size was demonstrated to be the prime microstructure parameter associated with the beneficial effect on the strength of the Sn-0.5wt.%Cu(-x)Al alloys. Full article

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20 pages, 4116 KiB

Open AccessFeature PaperArticle

Size Effects of High Strength Steel Wires

by Kanji Ono

Metals 2019, 9(2), 240; https://doi.org/10.3390/met9020240 - 17 Feb 2019

Cited by 10 | Viewed by 4480

Abstract

This study examines the effects of size on the strength of materials, especially on high strength pearlitic steel wires. These wires play a central role in many long span suspension bridges and their design, construction, and maintenance are important for global public safety. [...] Read more.

This study examines the effects of size on the strength of materials, especially on high strength pearlitic steel wires. These wires play a central role in many long span suspension bridges and their design, construction, and maintenance are important for global public safety. In particular, two relationships have been considered to represent strength variation with respect to length parameters: (i) the strength versus inverse square-root and (ii) inverse length equations. In this study, existing data for the strength of high strength pearlitic steel wires is evaluated for the coefficient of determination (R² values). It is concluded that the data fits into two equations equally well. Thus, the choice between two groups of theories that predict respective relationships must rely on the merit of theoretical developments and assumptions made. Full article

(This article belongs to the Special Issue Dislocation Mechanics of Metal Plasticity and Fracturing)

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