Editorial

3 pages, 158 KiB

Open AccessEditorial

Microstructural and Mechanical Characterization of Alloys

by Marek Sroka and Grzegorz Golański

Crystals 2020, 10(10), 945; https://doi.org/10.3390/cryst10100945 - 17 Oct 2020

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This Special Issue on “Microstructural and Mechanical Characterization of Alloys” features eight papers that cover the recent developments in alloys (engineering materials), methods of improvement of strength and cyclic properties of alloys, the stability of microstructure, the possible application of new (or improved) [...] Read more.

This Special Issue on “Microstructural and Mechanical Characterization of Alloys” features eight papers that cover the recent developments in alloys (engineering materials), methods of improvement of strength and cyclic properties of alloys, the stability of microstructure, the possible application of new (or improved) alloys, and the use of treatment for alloy improvement. Full article

(This article belongs to the Special Issue Microstructural and Mechanical Characterization of Alloys)

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13 pages, 7308 KiB

Open AccessArticle

Effect of Equal Channel Angular Pressing on Microstructure and Mechanical Properties of a Cu-Mg Alloy

by Muzhi Ma, Xi Zhang, Zhou Li, Zhu Xiao, Hongyun Jiang, Ziqi Xia and Hanyan Huang

Crystals 2020, 10(6), 426; https://doi.org/10.3390/cryst10060426 - 27 May 2020

Cited by 11 | Viewed by 2385

Abstract

A Cu-0.43Mg (wt.%) alloy was processed by equal channel angular pressing (ECAP) up to eight passes via a processing route (Bc). The hardness distribution on the longitudinal and transverse sections was collected and the microstructure in the central and bottom regions on the [...] Read more.

A Cu-0.43Mg (wt.%) alloy was processed by equal channel angular pressing (ECAP) up to eight passes via a processing route (Bc). The hardness distribution on the longitudinal and transverse sections was collected and the microstructure in the central and bottom regions on the longitudinal section was examined. The result showed that the hardness was improved significantly at the initial stage of the ECAP process, and the lower hardness region appeared at the area nearby the bottom surface. With the number of ECAP passes, the hardness gently increased and finally became saturated. The inhomogeneity of the hardness distribution along the normal direction gradually weakened and finally disappeared. The shear microstructure in the central region was different from that in the bottom region after one ECAP pass, and they became similar to each other after two ECAP passes, except the rotation angle of the elongated grains. With the further increasing ECAP passes, there was no obvious microstructure difference between the central and bottom regions. The inhomogeneities of the hardness and the microstructure along the normal direction in the alloy after one ECAP passes should be attributed to the non-zero outer arc of curvature of the ECAP die and the friction between the bottom surface of the billets and the ECAP die walls. The yield strength of the alloy increased from 124 MPa before the ECAP process to 555 MPa after eight ECAP passes. The improvement of yield strengths of the ECAPed Cu-Mg alloy should be mainly attributed to the dislocation strengthening and the grain boundary strengthening. Full article

(This article belongs to the Special Issue Microstructural and Mechanical Characterization of Alloys)

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15 pages, 7473 KiB

Open AccessArticle

Hot Deformation Behavior and Microstructure Characterization of an Al-Cu-Li-Mg-Ag Alloy

by Lingfei Cao, Bin Liao, Xiaodong Wu, Chaoyang Li, Guangjie Huang and Nanpu Cheng

Crystals 2020, 10(5), 416; https://doi.org/10.3390/cryst10050416 - 22 May 2020

Cited by 17 | Viewed by 2707

Abstract

The flow behavior of an Al-Cu-Li-Mg-Ag alloy was studied by thermal simulation tests at deformation temperatures between 350 °C and 470 °C and strain rates between 0.01–10 s⁻¹. The microstructures of the deformed materials were characterized by electron backscattered diffraction. Constitutive [...] Read more.

The flow behavior of an Al-Cu-Li-Mg-Ag alloy was studied by thermal simulation tests at deformation temperatures between 350 °C and 470 °C and strain rates between 0.01–10 s⁻¹. The microstructures of the deformed materials were characterized by electron backscattered diffraction. Constitutive equations were developed after considering compensation for strains. The processing maps were established and the optimum processing window was identified. The experimental data and predicted values of flow stresses were in a good agreement with each other. The influence of deformation temperature and strain rates on the microstructure were discussed. The relationship between the recrystallization mechanism and the Zener–Hollomon parameter was investigated as well. Full article

(This article belongs to the Special Issue Microstructural and Mechanical Characterization of Alloys)

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17 pages, 4371 KiB

Open AccessArticle

Mathematical Modeling and Analysis of Tribological Properties of AA6063 Aluminum Alloy Reinforced with Fly Ash by Using Response Surface Methodology

by Alaa Mohammed Razzaq, Dayang Laila Majid, Mohamad Ridzwan Ishak and Uday Muwafaq Basheer

Crystals 2020, 10(5), 403; https://doi.org/10.3390/cryst10050403 - 16 May 2020

Cited by 9 | Viewed by 3401

Abstract

Lightweight, high-strength metal matrix composites have attracted considerable interest because of their attractive physical, mechanical and tribological properties. Moreover, they may offer distinct advantages due to good strength and wear resistance. In this research, AA6063 was reinforced with FA particles using compocasting methods. [...] Read more.

Lightweight, high-strength metal matrix composites have attracted considerable interest because of their attractive physical, mechanical and tribological properties. Moreover, they may offer distinct advantages due to good strength and wear resistance. In this research, AA6063 was reinforced with FA particles using compocasting methods. The effects of fly ash content, load, sliding speed and performance tribology of AA6063 –FA composite were evaluated. Dry sliding wear tests were carried out according to experimental design using the pin-on-disc method with three different loads (24.5, 49 and 73.5 N) and three speeds (150, 200 and 250 rpm) at room temperature. Response surface methodology (RSM) was used to analyze the influence of the process parameters on the tribological behavior of the composites. The surface plot showed that the wear rate increased with increasing load, time and sliding velocity. In contrast, the friction coefficient decreased with increasing these parameters. Optimal models for wear rate and friction coefficient showed appropriate results that can be estimated, hence reducing wear testing time and cost. Full article

(This article belongs to the Special Issue Microstructural and Mechanical Characterization of Alloys)

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14 pages, 5730 KiB

Open AccessArticle

Simulation and Prediction of the Vickers Hardness of AZ91 Magnesium Alloy Using Artificial Neural Network Model

by Alaa F. Abd El-Rehim, Heba Y. Zahran, Doaa M. Habashy and Hana M. Al-Masoud

Crystals 2020, 10(4), 290; https://doi.org/10.3390/cryst10040290 - 10 Apr 2020

Cited by 13 | Viewed by 3017

Abstract

In this study, an artificial neural network (ANN) model was used to simulate and predict the Vickers hardness of AZ91 magnesium alloy. The samples of AZ91 alloy were aged at different temperatures (T_a = 100 to 300 °C) for different durations [...] Read more.

In this study, an artificial neural network (ANN) model was used to simulate and predict the Vickers hardness of AZ91 magnesium alloy. The samples of AZ91 alloy were aged at different temperatures (T_a = 100 to 300 °C) for different durations (t_a = 4 to 192 h) followed by water quenching at 25 °C. The age-hardening response of the samples was investigated by hardness measurements. The microstructure investigations showed that only discontinuous precipitates formed at low aging temperatures (100 and 150 °C), while continuous precipitates invaded all the samples at a high aging temperature (300 °C). Both discontinuous and continuous precipitates formed at the intermediate aging temperatures (200 and 250 °C). X-ray diffraction (XRD) analysis revealed that the microstructure comprised two phases: The α-Mg matrix and intermetallic β-Mg₁₇Al₁₂ phase. The alteration of the crystalline lattice parameters a, c, and c/a ratio with the aging time at various aging temperatures was also investigated. Both c and c/a ratio had the same behavior with aging time while a had an inverse trend. The observed variations of the lattice parameters were attributed to the mode of precipitation in AZ91 alloy. The ANN findings for the simulation and prediction perfectly conformed to the experimental data. Full article

(This article belongs to the Special Issue Microstructural and Mechanical Characterization of Alloys)

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16 pages, 5845 KiB

Open AccessArticle

Microstructural Stability and Softening Resistance of a Novel Hot-Work Die Steel

by Ningyu Du, Hongwei Liu, Paixian Fu, Hanghang Liu, Chen Sun, Yanfei Cao and Dianzhong Li

Crystals 2020, 10(4), 238; https://doi.org/10.3390/cryst10040238 - 25 Mar 2020

Cited by 16 | Viewed by 3144

Abstract

A novel hot-work die steel, named 5Cr5Mo2, was designed to obtain superior thermal stability. The proposed alloy is evaluated in terms of its hardness, microstructure, and tempering kinetics. Compared with the commonly used H13 steel, the softening resistance of the designed steel is [...] Read more.

A novel hot-work die steel, named 5Cr5Mo2, was designed to obtain superior thermal stability. The proposed alloy is evaluated in terms of its hardness, microstructure, and tempering kinetics. Compared with the commonly used H13 steel, the softening resistance of the designed steel is superior. Based on SEM and transmission electron microscopy (TEM) observations, a higher abundance of fine molybdenum carbides precipitate in 5Cr5Mo2 steel. Strikingly, the coarseness rate of the carbides is also relatively low during the tempering treatment. Moreover, owing to their pinning effect on dislocation slip, the dislocation density of the 5Cr5Mo2 steel decreases more slowly than that of the H13 steel. Furthermore, a mathematical softening model was successfully deduced and verified by analyzing the tempering kinetics. This model can be used to predict the hardness evolution of the die steels during the service period at high temperature. Full article

(This article belongs to the Special Issue Microstructural and Mechanical Characterization of Alloys)

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12 pages, 12639 KiB

Open AccessArticle

The Effect of Lath Martensite Microstructures on the Strength of Medium-Carbon Low-Alloy Steel

by Chen Sun, Paixian Fu, Hongwei Liu, Hanghang Liu, Ningyu Du and Yanfei Cao

Crystals 2020, 10(3), 232; https://doi.org/10.3390/cryst10030232 - 23 Mar 2020

Cited by 36 | Viewed by 4000

Abstract

Different austenitizing temperatures were used to obtain medium-carbon low-alloy (MCLA) martensitic steels with different lath martensite microstructures. The hierarchical microstructures of lath martensite were investigated by optical microscopy (OM), electron backscattering diffraction (EBSD), and transmission electron microscopy (TEM). The results show that with [...] Read more.

Different austenitizing temperatures were used to obtain medium-carbon low-alloy (MCLA) martensitic steels with different lath martensite microstructures. The hierarchical microstructures of lath martensite were investigated by optical microscopy (OM), electron backscattering diffraction (EBSD), and transmission electron microscopy (TEM). The results show that with increasing the austenitizing temperature, the prior austenite grain size and block size increased, while the lath width decreased. Further, the yield strength and tensile strength increased due to the enhancement of the grain boundary strengthening. The fitting results reveal that only the relationship between lath width and strength followed the Hall–Petch formula of. Hence, we propose that lath width acts as the effective grain size (EGS) of strength in MCLA steel. In addition, the carbon content had a significant effect on the EGS of martensitic strength. In steels with lower carbon content, block size acted as the EGS, while, in steels with higher carbon content, the EGS changed to lath width. The effect of the Cottrell atmosphere around boundaries may be responsible for this change. Full article

(This article belongs to the Special Issue Microstructural and Mechanical Characterization of Alloys)

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13 pages, 6267 KiB

Open AccessArticle

Comparison of the Crystal Structure and Wear Resistance of Co-Based Alloys with Low Carbon Content Manufactured by Selective Laser Sintering and Powder Injection Molding

by Anna Ziębowicz, Krzysztof Matus, Wojciech Pakieła, Grzegorz Matula and Miroslawa Pawlyta

Crystals 2020, 10(3), 197; https://doi.org/10.3390/cryst10030197 - 13 Mar 2020

Cited by 10 | Viewed by 3147

Abstract

Cobalt alloys are widely used in biomedicine, implantology, and dentistry due to their high corrosion resistance and good mechanical properties. The high carbon improves the wear properties, but causes fragility and dangerous cracking of elements during use. The aim of the present work [...] Read more.

Cobalt alloys are widely used in biomedicine, implantology, and dentistry due to their high corrosion resistance and good mechanical properties. The high carbon improves the wear properties, but causes fragility and dangerous cracking of elements during use. The aim of the present work was to analyze and compare the structure and wear resistance of Co-based alloy samples with low carbon content, produced by Selective Laser Sintering (SLS) and Powder Injection Molding (PIM). Structure characterization, mainly with the use of transmission electron microscopy, was applied to investigate the differences in tribological properties. The better resistance to abrasive wear for SLS was explained by the presence of a hard, intermetallic phase, present as precipitates limited in size and evenly distributed in the cobalt matrix. The second factor was the structure of the cobalt matrix, with dominant content of the hexagonal phase. By combining the characteristic features of the matrix and the reinforcing phase, the analyzed material gains an additional advantage, namely a higher resistance to abrasive wear. Full article

(This article belongs to the Special Issue Microstructural and Mechanical Characterization of Alloys)

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12 pages, 5601 KiB

Open AccessArticle

Effect of ECAP on the Microstructure and Mechanical Properties of a Rolled Mg-2Y-0.6Nd-0.6Zr Magnesium Alloy

by Xiaofang Shi, Wei Li, Weiwei Hu, Yun Tan, Zhenglai Zhang and Liang Tian

Crystals 2019, 9(11), 586; https://doi.org/10.3390/cryst9110586 - 08 Nov 2019

Cited by 5 | Viewed by 2263

Abstract

A fine-grained Mg-2Y-0.6Nd-0.6Zr alloy was processed by bar-rolling and equal-channel angular pressing (ECAP). The effect of ECAP on the microstructure and mechanical properties of rolled Mg-2Y-0.6Nd-0.6Zr alloy was investigated by optical microscopy, scanning electron microscopy, electron backscattered diffraction and a room temperature tensile [...] Read more.

A fine-grained Mg-2Y-0.6Nd-0.6Zr alloy was processed by bar-rolling and equal-channel angular pressing (ECAP). The effect of ECAP on the microstructure and mechanical properties of rolled Mg-2Y-0.6Nd-0.6Zr alloy was investigated by optical microscopy, scanning electron microscopy, electron backscattered diffraction and a room temperature tensile test. The results show that the Mg-2Y-0.6Nd-0.6Zr alloy obtained high strength and poor plasticity after rolling. As the number of ECAP passes increased, the grain size of the alloy gradually reduced and the texture of the basal plane gradually weakened. The ultimate tensile strength of the alloy first increased and then decreased, the yield strength gradually decreased, and the plasticity continuously increased. After four passes of ECAP, the average grain size decreased from 11.2 µm to 1.87 µm, and the alloy obtained excellent comprehensive mechanical properties. Its strength was slightly reduced compared to the as-rolled alloy, but the plasticity was greatly increased. Full article

(This article belongs to the Special Issue Microstructural and Mechanical Characterization of Alloys)

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