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Microstructure and Mechanical Properties of Metals and Alloys

A special issue of Materials (ISSN 1996-1944). This special issue belongs to the section "Smart Materials".

Deadline for manuscript submissions: closed (30 November 2021) | Viewed by 49201

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Division of Light Metal, Korea Institute of Materials Science (KIMS), Seongsan-gu, Changwon-si 51508, Gyeongsangnam-do, Republic of Korea
Interests: material characterization; mechanical properties; materials; light alloys
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Special Issue Information

Dear Colleagues,

Metals and alloys have played important roles in enabling modern structural designs in practice. This Special Issue seeks to collect various scientific and/or engineering reports pertaining to research on metals and alloys that present applicable advances of our knowledge of the structures, properties, and performance capabilities of these materials. Affordable processing and fabrication methods as well as characterization and evaluation methods are also crucial topics related to the wider application of metallic materials in both academia and industry. Starting with the microstructural and mechanical properties of metals and alloying, appropriate correlations among the processing, properties, and performance characteristics will lead to a better understanding of the nature of these materials and improve their engineering application capabilities. Various theoretical and experimental approaches to assessing the mechanical behaviors of these materials are a basic concern of many materials researchers. Numerical and computational approaches can also herald new challenges and enrich our insight into new means of the exploitation of new metallic alloying systems. Plastic deformation and subsequent heat treatments cause various microstructural changes and thus alter important mechanical properties. Lightweight metals have also attracted much attention as potential design materials for automobiles, electronics, and sporting equipment, in addition to potentially meeting the demands of better fuel efficiency or CO2 reductions.

This Special Issue aims to focus on the processing, microstructure, and mechanical properties of metals and alloys within a materials relationship framework including, but not limited to, the following topics:

  • Fabrication and processing of metallic materials and alloys for microstructural and mechanical control of properties, such as casting, thermo-mechanical processing, metal forming, bonding and welding;
  • Characterizations and evaluations of metallic materials and alloys based on various methodologies, including theoretical and numerical methods and microscopy and mechanical testing;
  • Deformation, recrystallization, and grain growth based on microstructures, morphologies, textures, and anisotropy characteristics;
  • Lightweight structural metallic materials, such as alloys containing aluminum and magnesium, as well as other metals;
  • Special applications of metallic materials, such as high-temperature-resistant materials, corrosion-resistant materials, bio-degradable metals, and advanced high-strength steels.

Dr. Jae-Hyung Cho
Guest Editor

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Keywords

  • microstructure
  • texture
  • mechanical properties
  • fabrication and processing
  • characterization and evaluation
  • deformation and annealing
  • metals and alloys

Published Papers (17 papers)

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Research

18 pages, 19164 KiB  
Article
Analysis of Microstructure Evolution and Mechanical Properties during Compression of Open-Cell Ni-Foams with Hollow Struts Using Micro-CT and FEM
by Jun Ho Lee, Geon Young Lee, Jong-joo Rha, Ji Hoon Kim and Jae-Hyung Cho
Materials 2022, 15(1), 124; https://0-doi-org.brum.beds.ac.uk/10.3390/ma15010124 - 24 Dec 2021
Cited by 4 | Viewed by 2066
Abstract
Based on electron backscatter diffraction (EBSD), hollow structures of Ni foam struts fabricated by electroplating on a chemically removable template were observed. Three-dimensional (3D) pore structures of Ni foams were also obtained using X-ray computed tomography (CT), and microstructural features such as porosity, [...] Read more.
Based on electron backscatter diffraction (EBSD), hollow structures of Ni foam struts fabricated by electroplating on a chemically removable template were observed. Three-dimensional (3D) pore structures of Ni foams were also obtained using X-ray computed tomography (CT), and microstructural features such as porosity, pore size and strut thickness were statistically quantified. Evolution of microstructure and mechanical properties during ex situ compression of open-cell Ni-foams was investigated based on X-ray CT, and experimental results were compared with predictions by the finite element method (FEM). 3D microstructures obtained by X-ray CT revealed that the stress drop started with the buckling of struts at the center of the Ni-foams. The flow stress increased after the buckling of the struts spreads to most of the regions. For effective simulation of the compressive deformation and determination of the microstructural evolution, small domains of interest were selected from the entire set of observed 3D microstructures based on X-ray CT, and struts of Ni foams with a hollow structure were simplified with relevant thin-solid struts. Numerical 3D modeling comprehensively disclosed that compression caused the transverse buckling of the struts, with the bending and buckling of struts thus reducing the stress. Thickness variation of the struts causes a change in the porosity of Ni-foams without a change in pore shape or connectivity. The overall range of strut thickness was from 59 to 133 μm, and the range of porosity values was from 80% to 93.7%. A stress drop was predicted with a decrease in the strut thickness or an increase in the porosity, as measured experimentally. It was also found that the stress drop contributed to an increase in the calculated energy absorption efficiency. Full article
(This article belongs to the Special Issue Microstructure and Mechanical Properties of Metals and Alloys)
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13 pages, 2528 KiB  
Article
The Effect of Heat Treatment on the Corrosion Resistance of Fe-Based Amorphous Alloy Coating Prepared by High Velocity Oxygen Fuel Method
by Chun-Ying Lee, Hung-Hua Sheu, Leu-Wen Tsay, Po-Sen Hsiao, Tzu-Jing Lin and Hung-Bin Lee
Materials 2021, 14(24), 7818; https://0-doi-org.brum.beds.ac.uk/10.3390/ma14247818 - 17 Dec 2021
Cited by 4 | Viewed by 1903
Abstract
In this study, Fe40Cr19Mo18C15B8 amorphous coatings were prepared using high velocity oxygen fuel (HVOF) technology. Different temperatures were used in the heat treatment (600 °C, 650 °C, and 700 °C) and the annealed coatings [...] Read more.
In this study, Fe40Cr19Mo18C15B8 amorphous coatings were prepared using high velocity oxygen fuel (HVOF) technology. Different temperatures were used in the heat treatment (600 °C, 650 °C, and 700 °C) and the annealed coatings were analyzed by DSC, SEM, TEM, and XRD. XRD and DSC results showed that the coating started to form a crystalline structure after annealing at 650 °C. From the SEM observation, it can be found that when the annealing temperature of the Fe-based amorphous alloy coating reached 700 °C, the surface morphology of the coating became relatively flat. TEM observation showed that when the annealing temperature of the Fe-based amorphous alloy coating was 700 °C, crystal grains in the coating recrystallized with a grain size of 5–20 nm. SAED analysis showed that the precipitated carbide phase was M23C6 phase with different crystal orientations (M = Fe, Cr, Mo). Finally, the corrosion polarization curve showed that the corrosion current density of the coating after annealing only increased by 9.13 μA/cm2, which indicated that the coating after annealing treatment still had excellent corrosion resistance. It also proved that the Fe-based amorphous alloy coating can be used in high-temperature environments. XPS analysis showed that after annealing FeO and Fe2O3 oxide components increased, and the formation of a large number of crystals in the coating resulted in a decrease in corrosion resistance. Full article
(This article belongs to the Special Issue Microstructure and Mechanical Properties of Metals and Alloys)
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17 pages, 10684 KiB  
Article
Quantitative Strengthening Evaluation of Powder Metallurgy Titanium Alloys with Substitutional Zr and Interstitial O Solutes via Homogenization Heat Treatment
by Katsuyoshi Kondoh, Shota Kariya, Anak Khantachawana, Abdulaziz Alhazaa and Junko Umeda
Materials 2021, 14(21), 6561; https://0-doi-org.brum.beds.ac.uk/10.3390/ma14216561 - 01 Nov 2021
Cited by 3 | Viewed by 1610
Abstract
The decomposition behavior of ZrO2 particles and uniform distribution of Zr and O solutes were investigated by employing in situ scanning electron microscope-electron backscatter diffraction (SEM-EBSD) analysis and thermogravimetric-differential thermal analysis (TG-DTA) to optimize the process conditions in preparing Ti-Zr-O alloys from [...] Read more.
The decomposition behavior of ZrO2 particles and uniform distribution of Zr and O solutes were investigated by employing in situ scanning electron microscope-electron backscatter diffraction (SEM-EBSD) analysis and thermogravimetric-differential thermal analysis (TG-DTA) to optimize the process conditions in preparing Ti-Zr-O alloys from the pre-mixed pure Ti powder and ZrO2 particles. The extruded Ti-Zr-O alloys via homogenization and water-quenching treatment were found to have a uniform distribution of Zr and O solutes in the matrix and also showed a remarkable improvement in the mechanical properties, for example, the yield stress of Ti-3 wt.% ZrO2 sample (1144.5 MPa) is about 2.5 times more than the amount of yield stress of pure Ti (471.4 MPa). Furthermore, the oxygen solid-solution was dominant in the yield stress increment, and the experimental data agreed well with the calculation results estimated using the Hall-Petch equation and Labusch model. Full article
(This article belongs to the Special Issue Microstructure and Mechanical Properties of Metals and Alloys)
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13 pages, 5074 KiB  
Article
Factors Affecting the Microstructure, Tensile Properties and Corrosion Resistance of AA7075 Forgings
by Teng-Shih Shih, Ho-Tieh Hsu and Lih-Ren Hwang
Materials 2021, 14(19), 5776; https://0-doi-org.brum.beds.ac.uk/10.3390/ma14195776 - 02 Oct 2021
Viewed by 1728
Abstract
AA7075 alloys are high strength alloys and are used as an important material for making engineering parts. Forged AA7075 alloys showed significantly decreased toughness when the material was hot deformed at a high temperature. This study investigated the effects of forging parameters on [...] Read more.
AA7075 alloys are high strength alloys and are used as an important material for making engineering parts. Forged AA7075 alloys showed significantly decreased toughness when the material was hot deformed at a high temperature. This study investigated the effects of forging parameters on the tensile properties and the microstructure of AA7075 forgings. The tensile properties and corrosion resistance of different forgings were determined to be correlated with their microstructures. The experiment annealed and hot-deformed sample bars at 633 K, cold-deformed them at room temperature (RF), and at sub-zero temperatures (CF). After T73 heat treatment, the microstructures depended on the deformation temperature. This varied significantly, from elongated grains for hot-forged samples to equiaxial grains for cold-deformed samples. The hot-deformed samples had a tensile strength of 592 MPa for UTS, 538 MPa for YS, and 13.4% for elongation. These were stronger but less elongated than the cold-deformed samples. All hot-deformed (HF), RF, and CF samples exhibited mechanical properties that exceeded UTS > 505 MPa, YS > 435 MPa, and an elongation > 13%, and showed moderate corrosion resistance if samples were in contact with a 3.5 wt.% NaCl solution. The toughness of the forgings could be significantly improved by decreasing the forging temperatures. The corrosion resistance of AA7075-T73 forgings was affected by the total grain boundary (GB) lengths per unit area and the 2nd phase particle counts per unit area. Increasing the high-angle grain boundary lengths (HAGBs) per unit area accelerated corrosion and increased the Icorr value. Full article
(This article belongs to the Special Issue Microstructure and Mechanical Properties of Metals and Alloys)
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24 pages, 15314 KiB  
Article
Modeling and Experimental Results of Selected Lightweight Complex Concentrated Alloys, before and after Heat Treatment
by Dumitru Mitrica, Ioana Cristina Badea, Mihai Tudor Olaru, Beatrice Adriana Serban, Denisa Vonica, Marian Burada, Victor Geanta, Adrian Nicolae Rotariu, Florentin Stoiciu, Viorel Badilita and Lidia Licu
Materials 2020, 13(19), 4330; https://0-doi-org.brum.beds.ac.uk/10.3390/ma13194330 - 29 Sep 2020
Cited by 11 | Viewed by 2430
Abstract
Lightweight complex concentrated alloys (LWCCA), composed of elements with low density, have become a great area of interest due to the high demand in a large number of applications. Previous research on LWCCAs was focused on high entropy multicomponent alloy systems that provide [...] Read more.
Lightweight complex concentrated alloys (LWCCA), composed of elements with low density, have become a great area of interest due to the high demand in a large number of applications. Previous research on LWCCAs was focused on high entropy multicomponent alloy systems that provide low density and high capability of solid solution formation. Present research introduces two alloy systems (Al-Cu-Si-Zn-Mg and Al-Mn-Zn-Mg-Si) that contain readily available and inexpensive starting materials and have potential for solid solution formation structures. For the selection of appropriate compositions, authors applied semi-empirical criteria and optimization software. Specialized modeling software (MatCalc) was used to determine probable alloy structures by CALPHAD, non-equilibrium solidification and kinetic simulations. The selected alloys were prepared in an induction furnace. Specimens were heat treated to provide stable structures. Physicochemical, microstructural, and mechanical characterization was performed for the selected alloy compositions. Modeling and experimental results indicated solid solution-based structures in the as-cast and heat-treated samples. Several intermetallic phases were present at higher concentrations than in the conventional alloys. Alloys presented a brittle structure with compression strength of 486–618 MPa and hardness of 268–283 HV. The potential for uniform intermetallic phase distribution in the selected alloys makes them good candidates for applications were low weight and high resistance is required. Full article
(This article belongs to the Special Issue Microstructure and Mechanical Properties of Metals and Alloys)
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16 pages, 7463 KiB  
Article
Effects of Cooling Rate during Quenching and Tempering Conditions on Microstructures and Mechanical Properties of Carbon Steel Flange
by Haeju Jo, Moonseok Kang, Geon-Woo Park, Byung-Jun Kim, Chang Yong Choi, Hee Sang Park, Sunmi Shin, Wookjin Lee, Yong-Sik Ahn and Jong Bae Jeon
Materials 2020, 13(18), 4186; https://0-doi-org.brum.beds.ac.uk/10.3390/ma13184186 - 21 Sep 2020
Cited by 10 | Viewed by 6987
Abstract
This study investigated the mechanical properties of steel in flanges, with the goal of obtaining high strength and high toughness. Quenching was applied alone or in combination with tempering at one of nine combinations of three temperatures TTEM and durations tTEM [...] Read more.
This study investigated the mechanical properties of steel in flanges, with the goal of obtaining high strength and high toughness. Quenching was applied alone or in combination with tempering at one of nine combinations of three temperatures TTEM and durations tTEM. Cooling rates at various flange locations during quenching were first estimated using finite element method simulation, and the three locations were selected for mechanical testing in terms of cooling rate. Microstructures of specimens were observed at each condition. Tensile test and hardness test were performed at room temperature, and a Charpy impact test was performed at −46 °C. All specimens had a multiphase microstructure composed of matrix and secondary phases, which decomposed under the various tempering conditions. Decrease in cooling rate (CR) during quenching caused reduction in hardness and strength but did not affect low-temperature toughness significantly. After tempering, hardness and strength were reduced and low-temperature toughness was increased. Microstructures and mechanical properties under the various tempering conditions and CRs during quenching were discussed. This work was based on the properties directly obtained from flanges under industrial processes and is thus expected to be useful for practical applications. Full article
(This article belongs to the Special Issue Microstructure and Mechanical Properties of Metals and Alloys)
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20 pages, 7093 KiB  
Article
The Influence of the Third Element on Nano-Mechanical Properties of Iron Borides FeB and Fe2B Formed in Fe-B-X (X = C, Cr, Mn, V, W, Mn + V) Alloys
by Ivana Kirkovska, Viera Homolová, Ivan Petryshynets and Tamás Csanádi
Materials 2020, 13(18), 4155; https://0-doi-org.brum.beds.ac.uk/10.3390/ma13184155 - 18 Sep 2020
Cited by 2 | Viewed by 2184
Abstract
In this study, the influence of alloying elements on the mechanical properties of iron borides FeB and Fe2B formed in Fe-B-X (X = C, Cr, Mn, V, W, Mn + V) alloys were evaluated using instrumented indentation measurement. The microstructural characterization [...] Read more.
In this study, the influence of alloying elements on the mechanical properties of iron borides FeB and Fe2B formed in Fe-B-X (X = C, Cr, Mn, V, W, Mn + V) alloys were evaluated using instrumented indentation measurement. The microstructural characterization of the alloys was performed by means of X-ray diffraction and scanning electron microscope equipped with an energy dispersive X-ray analyzer. The fraction of the phases present in the alloys was determined either by the lever rule or by image analysis. The hardest and stiffest FeB formed in Fe-B-X (X = C, Cr, Mn) alloys was observed in the Fe-B-Cr alloys, where indentation hardness of HIT = 26.9 ± 1.4 GPa and indentation modulus of EIT = 486 ± 22 GPa were determined. The highest hardness of Fe2B was determined in the presence of tungsten as an alloying element, HIT = 20.8 ± 0.9 GPa. The lowest indentation hardness is measured in manganese alloyed FeB and Fe2B. In both FeB and Fe2B, an indentation size effect was observed, showing a decrease of hardness with increasing indentation depth. Full article
(This article belongs to the Special Issue Microstructure and Mechanical Properties of Metals and Alloys)
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19 pages, 23836 KiB  
Article
Microstructure and Texture Evolutions During Deep Drawing of Mg–Al–Mn Sheets at Elevated Temperatures
by Jae-Hyung Cho, Sang-Ho Han and Geon Young Lee
Materials 2020, 13(16), 3608; https://0-doi-org.brum.beds.ac.uk/10.3390/ma13163608 - 14 Aug 2020
Cited by 4 | Viewed by 2001
Abstract
Texture and microstructure evolution of ingot and twin-roll casted Mg–Al–Mn magnesium sheets were examined during deep drawing at elevated temperatures. The twin-roll casted sheets possessed smaller grain sizes and weaker basal intensity levels than the ingot-casted sheets. The strength and elongation at room [...] Read more.
Texture and microstructure evolution of ingot and twin-roll casted Mg–Al–Mn magnesium sheets were examined during deep drawing at elevated temperatures. The twin-roll casted sheets possessed smaller grain sizes and weaker basal intensity levels than the ingot-casted sheets. The strength and elongation at room temperature for the twin-roll casted sheets were greater than those of the ingot-casted sheets. At elevated temperatures, the ingot-casted sheets showed better elongation than the twin-roll casted sheets. Different size and density of precipitates were examined using transmission electron microscopy (TEM) for both ingot-casted and twin-roll-casted sheets. The deep drawing process was also carried out at various working temperatures and deformation rates, 225 °C to 350 °C and 30 mm/min to 50 mm/min, respectively. The middle wall part of cups were mainly tensile deformation, and the lower bent regions of drawn cups were most thinned region. Overall, the ingot-casted sheets revealed better deep drawability than the twin-roll casted sheets. Microstructure and texture evolution of the top, middle and lower parts of drawn cups were investigated using electron backscatter diffraction. Increased deformation rate is important to activate tensile twins both near the bent and flange areas. Ingot casted sheets revealed more tensile twins than twin-roll casted sheets. Increased working temperature is important to activate non-basal slips and produce the DRXed grain structure in the flange. Dynamic recrystallization were frequently found in the top flanges of the cups. Both tensile twins and non-basal slips contributed to occurrence of the dynamic recrystallization in the flange. Full article
(This article belongs to the Special Issue Microstructure and Mechanical Properties of Metals and Alloys)
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13 pages, 5660 KiB  
Article
Evaluation of Structure and Corrosion Behavior of FeAl Alloy after Crystallization, Hot Extrusion and Hot Rolling
by Janusz Cebulski, Dorota Pasek, Bartosz Chmiela, Magdalena Popczyk, Andrzej Szymon Swinarew, Arkadiusz Stanula, Zbigniew Waśkiewicz and Beat Knechtle
Materials 2020, 13(9), 2041; https://0-doi-org.brum.beds.ac.uk/10.3390/ma13092041 - 27 Apr 2020
Cited by 1 | Viewed by 1983
Abstract
The paper presents the results of tests on the corrosion resistance of Fe40Al5Cr0.2TiB alloy after casting, plastic working using extrusion and rolling methods. Examination of the microstructure of the Fe40Al5Cr0.2TiB alloy after casting and after plastic working was performed on an Olympus GX51 [...] Read more.
The paper presents the results of tests on the corrosion resistance of Fe40Al5Cr0.2TiB alloy after casting, plastic working using extrusion and rolling methods. Examination of the microstructure of the Fe40Al5Cr0.2TiB alloy after casting and after plastic working was performed on an Olympus GX51 light microscope. The stereological relationships of the alloy microstructure in the state after crystallization and after plastic working were determined. The quantitative analysis of the structure was conducted after testing with the EBSD INCA HKL detector and the Nordlys II analysis system (Channel 5), which was equipped with the Hitachi S-3400N microscope. Structure tests and corrosion tests were performed on tests cut perpendicular to the ingot axis, extrusion direction, and rolling direction. As a result of the tests, it was found that the crystallized alloy has better corrosion resistance than plastically processed material. Plastic working increases the intensity of the electrochemical corrosion of the examined alloy. It was found that as-cast alloy is the most resistant to corrosion in a 5% NaCl compared with the alloys after hot extrusion and after hot rolling. The parameters in this study show the smallest value of the corrosion current density and corrosion rate as well as the more positive value of corrosion potential. Full article
(This article belongs to the Special Issue Microstructure and Mechanical Properties of Metals and Alloys)
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16 pages, 17441 KiB  
Article
Influence of Copper Addition on Sigma Phase Precipitation during Hot Deformation of Duplex Steel
by Grzegorz Stradomski, Arkadiusz Szarek and Dariusz Rydz
Materials 2020, 13(7), 1665; https://0-doi-org.brum.beds.ac.uk/10.3390/ma13071665 - 03 Apr 2020
Cited by 1 | Viewed by 1996
Abstract
The paper presents an experimental study on microstructure changes in duplex steel after hot deformation. Duplex steels and cast steels are characterized by a multiphase microstructure. They are relatively new materials with great contributions to the many fields of industries. Due to the [...] Read more.
The paper presents an experimental study on microstructure changes in duplex steel after hot deformation. Duplex steels and cast steels are characterized by a multiphase microstructure. They are relatively new materials with great contributions to the many fields of industries. Due to the fact of deforming two different phase austenite and ferrite those materials have a complex plasticity. This work is a continuation and complementation of previous works and is a significant supplement to information presented in them. The article concerns precipitation phenomena and changes in the microstructure of two grades of ferritic-austenitic steels: X2CrNiMoN25-7-4 and X2CrNiMoCuN25-6-3. Those steels have a very similar chemical composition, differing by only 2.5% copper content. An important aspect presented in the work is we observed that adding 2.5% copper prevented precipitation of the destructive sigma phase during the hot deformation. Full article
(This article belongs to the Special Issue Microstructure and Mechanical Properties of Metals and Alloys)
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12 pages, 8292 KiB  
Article
Micro-Texture Analyses of a Cold-Work Tool Steel for Additive Manufacturing
by Jun-Yun Kang, Jaecheol Yun, Byunghwan Kim, Jungho Choe, Sangsun Yang, Seong-Jun Park, Ji-Hun Yu and Yong-Jin Kim
Materials 2020, 13(3), 788; https://0-doi-org.brum.beds.ac.uk/10.3390/ma13030788 - 09 Feb 2020
Cited by 2 | Viewed by 2727
Abstract
Small objects of an alloy tool steel were built by selective laser melting at different scan speeds, and their microstructures were analyzed using electron backscatter diffraction (EBSD). To present an explicit correlation with the local thermal cycles in the objects, prior austenite grains [...] Read more.
Small objects of an alloy tool steel were built by selective laser melting at different scan speeds, and their microstructures were analyzed using electron backscatter diffraction (EBSD). To present an explicit correlation with the local thermal cycles in the objects, prior austenite grains were reconstructed using the EBSD mapping data. Extensive growth of austenitic grains after solidification could be detected by the disagreement between the networks of carbides and austenite grain boundaries. A rapid laser scan at 2000 mm/s led to less growth, but retained a larger amount of austenite than a slow one at 50 mm/s. The rapid scan also exhibited definite evolution of Goss-type textures in austenite, which could be attributed to the growth of austenitic grains under a steep temperature gradient. The local variations in the microstructures and the textures enabled us to speculate the locally different thermal cycles determined by the different process conditions, that is, scan speeds. Full article
(This article belongs to the Special Issue Microstructure and Mechanical Properties of Metals and Alloys)
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9 pages, 2607 KiB  
Article
Effects of Nb on the Microstructure and Compressive Properties of an As-Cast Ni44Ti44Nb12 Eutectic Alloy
by Shifeng Liu, Song Han, Liqiang Wang, Jingbo Liu and Huiping Tang
Materials 2019, 12(24), 4118; https://0-doi-org.brum.beds.ac.uk/10.3390/ma12244118 - 09 Dec 2019
Cited by 10 | Viewed by 2767
Abstract
The addition of Nb can form a eutectic phase with a NiTi matrix in a NiTi-based shape memory alloy, improving the transition hysteresis of the NiTi alloy. A Ni44Ti44Nb12 ingot was prepared using the vacuum induction melting technique. [...] Read more.
The addition of Nb can form a eutectic phase with a NiTi matrix in a NiTi-based shape memory alloy, improving the transition hysteresis of the NiTi alloy. A Ni44Ti44Nb12 ingot was prepared using the vacuum induction melting technique. Under compression deformation, the yield strength of the NiTi–Nb alloy is about 1000 MPa, the maximum compressive strength and strain can reach 3155 MPa and 43%, respectively. Ni44Ti44Nb12 exhibited a superelastic recovery similar to that of the as-cast NiTi50. Meanwhile, the loading–unloading cycle compression shows that the superelastic recovery strain reached a maximum value (2.32%) when the total strain was about 15%, and the superelasticity tends to rise first and then decrease as the strain increases. Full article
(This article belongs to the Special Issue Microstructure and Mechanical Properties of Metals and Alloys)
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13 pages, 2749 KiB  
Article
Quality Index Charts of Al-Si-Mg Semi Solid Alloys Subjected to Multiple Temperatures Aging Treatments and Different Quenching Media
by Khaled Ahmed Ragab, Mohamed Bouazara and X.-Grant Chen
Materials 2019, 12(11), 1834; https://0-doi-org.brum.beds.ac.uk/10.3390/ma12111834 - 06 Jun 2019
Cited by 7 | Viewed by 2720
Abstract
The use of quality index charts is considered as an effective mean for evaluating the mechanical performance of Aluminum alloys for industrial engineering applications. The current study was carried out to investigate the influences of multiple-interrupted temperatures aging and quenching media (water versus [...] Read more.
The use of quality index charts is considered as an effective mean for evaluating the mechanical performance of Aluminum alloys for industrial engineering applications. The current study was carried out to investigate the influences of multiple-interrupted temperatures aging and quenching media (water versus air) on the quality index performance and precipitations evolution of A357 Aluminum semi solid alloys. Regarding the lack of similar investigations applied on such alloys, the quality index charts were generated for Al-Si-Mg semi solid castings based on its tensile properties. These charts are used to determine the quality index, in MPa, as a simple mean for compromising the strength and ductility together in one value using the Drouzy model. The multiple temperatures aging cycles were applied to improve the quality index values of Al-Si-Mg semi solid alloys for enhancing its characteristic and performance to resist the mechanical failures relating to automotive dynamic parts. The evolution of Mg2Si hardening precipitates, formed for specific thermal aging cycles, was investigated using transmission electron microscopy (TEM). The results obtained in this work revealed that the optimum quality index values were obtained by the application of T6-thermal under-aging treatment cycles. The regression models, using a statistical design of experiments, indicated that the optimum strength and high-quality index values were obtained by the application of interrupted thermal aging cycles, mainly C2,3-T6/T4/T7 conditions. Full article
(This article belongs to the Special Issue Microstructure and Mechanical Properties of Metals and Alloys)
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14 pages, 5635 KiB  
Article
The Evolution and Distribution of Microstructures in High-Energy Laser-Welded X100 Pipeline Steel
by Gang Wang, Limeng Yin, Zongxiang Yao, Jinzhao Wang, Shan Jiang, Zhongwen Zhang and Cunguo Zuo
Materials 2019, 12(11), 1762; https://0-doi-org.brum.beds.ac.uk/10.3390/ma12111762 - 30 May 2019
Cited by 6 | Viewed by 2703
Abstract
High-energy beam welding was introduced for pipeline steel welding to reduce pipeline construction costs and improve the efficiency and safety of oil and gas transportation. Microstructures and their distribution in X100 laser-welded joints, which determine the joints’ strength and toughness, are discussed in [...] Read more.
High-energy beam welding was introduced for pipeline steel welding to reduce pipeline construction costs and improve the efficiency and safety of oil and gas transportation. Microstructures and their distribution in X100 laser-welded joints, which determine the joints’ strength and toughness, are discussed in this paper. Welded joints were prepared by an automatic 10,000-watt robot-based disc laser-welding platform for 12.8 mm thick X100 pipeline steel. Then, the grain, grain boundary, orientation, and distribution pattern of each zone of the welded joints were studied by optical microscopy (OM), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and electron backscattered diffraction (EBSD) analysis techniques. The results showed that the grain boundary density, contents of the high-angle and low-angle grain boundaries, distribution states, and evolution trends of coincident site lattice (CSL) grain boundaries were essentially the same in each zone from the base metal (BM) to the weld of the X100 pipeline steel laser-welded joint. The relative content of grain boundaries above 55°, which were composed of the Σ3 type CSL grain boundary, showed a considerable impact on the mechanical properties of the joint. The content of twin grain boundaries was closely related to the thermal cycles of laser welding, and the effect of the cooling rate was greater than that of the process of austenization. Full article
(This article belongs to the Special Issue Microstructure and Mechanical Properties of Metals and Alloys)
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12 pages, 5104 KiB  
Article
Advantages of the Application of the Temper Bead Welding Technique During Wet Welding
by Jacek Tomków, Grzegorz Rogalski, Dariusz Fydrych and Jerzy Łabanowski
Materials 2019, 12(6), 915; https://0-doi-org.brum.beds.ac.uk/10.3390/ma12060915 - 19 Mar 2019
Cited by 41 | Viewed by 6380
Abstract
Thermo-mechanically rolled S460ML steel was chosen for welding in underwater wet welding conditions by covered electrodes. The main aim of this study was to check the weldability for fillet welds in a water environment by controlled thermal severity (CTS) tests and to check [...] Read more.
Thermo-mechanically rolled S460ML steel was chosen for welding in underwater wet welding conditions by covered electrodes. The main aim of this study was to check the weldability for fillet welds in a water environment by controlled thermal severity (CTS) tests and to check the influence of temper bead welding (TBW) on the weldability of the investigated steel. Non-destructive and destructive tests showed that S460ML steel has a high susceptibility to cold cracking. In all joints, hardness in the heat-affected zone (HAZ) was extended to the 400 HV10 values. Microscopic testing showed the presence of microcracks in the HAZ of all welded joints. TBW was chosen as the method to improve the weldability of the investigated steel. This technique allows for the reduction of the maximum hardness in the HAZ below the critical value of 380 HV10, as stated by the EN-ISO 15614-1:2017. It was determined that for S460ML steel, from the point of view of weldability, the pitch between two beads should be in the range 75%–100%. Also, if the pitch between two beads increases, the hardness, grain size, and number of cracks decreases. In all specimens where the hardness of the HAZ was below 380 HV10, there were no microcracks. Full article
(This article belongs to the Special Issue Microstructure and Mechanical Properties of Metals and Alloys)
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16 pages, 13367 KiB  
Article
Embrittlement Due to Excess Heat Input into Friction Stir Processed 7075 Alloy
by Ming-Hsiang Ku, Fei-Yi Hung and Truan-Sheng Lui
Materials 2019, 12(2), 227; https://0-doi-org.brum.beds.ac.uk/10.3390/ma12020227 - 10 Jan 2019
Cited by 1 | Viewed by 2199
Abstract
The grain size of high strength 7075 hot-rolled aluminum plates was refined by a friction stir process (FSP) to improve their mechanical properties. The results of the tensile ductility tests, which were conducted at various tool rotational speeds, in the friction stir zone [...] Read more.
The grain size of high strength 7075 hot-rolled aluminum plates was refined by a friction stir process (FSP) to improve their mechanical properties. The results of the tensile ductility tests, which were conducted at various tool rotational speeds, in the friction stir zone indicate significant tensile ductility loss, which even resulted in a ductile-to-brittle transition (DBT). DBT depends on the tool rotational speed. Our 1450 rpm specimens showed large data fluctuation in the tensile ductility and the location of the fracture controlled the formation of friction stir induced bands (FSIB). The crack initiation site located at FSIB was due to the tool rotational speed (1670 rpm). A higher heat-input causes the formation of FSIB, which is accompanied with micro-voids. This contributes significantly to tensile cracking within the stir zone after the application of the aging treatment. This investigation aimed to determine the dominant factor causing tensile ductility loss at the stir zone, which is the major restriction preventing further applications. Full article
(This article belongs to the Special Issue Microstructure and Mechanical Properties of Metals and Alloys)
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14 pages, 4534 KiB  
Article
Inhomogeneity of Free Volumes in Metallic Glasses under Tension
by Wei Da, Peng-wei Wang, Yi-fu Wang, Ming-fei Li and Liang Yang
Materials 2019, 12(1), 98; https://0-doi-org.brum.beds.ac.uk/10.3390/ma12010098 - 29 Dec 2018
Cited by 18 | Viewed by 3031
Abstract
In this work, the deformation of Zr2Cu metallic glass (MG) under uniaxial tensile stress was investigated at the atomic level using a series of synchrotron radiation techniques combined with molecular dynamics simulation. A new approach to the quantitative detection of free [...] Read more.
In this work, the deformation of Zr2Cu metallic glass (MG) under uniaxial tensile stress was investigated at the atomic level using a series of synchrotron radiation techniques combined with molecular dynamics simulation. A new approach to the quantitative detection of free volumes in MGs was designed and it was found that free volumes increase in the elastic stage, slowly expand in the yield stage, and finally reach saturation in the plastic stage. In addition, in different regions of the MG model, free volumes exhibited inhomogeneity under stress, in terms of size, density, and distribution. In particular, the expansion of free volumes in the center region was much more rapid than those in the other regions. It is interesting that the density of free volumes in the center region abnormally decreased with strain. It was revealed that the atomic-level stress between different regions may contribute to the inhomogeneity of free volumes under stress. In addition, the inhomogeneous change of free volumes during the deformation was confirmed by the evolution of local atomic shear strains in different regions. The present work provides in-depth insight into the deformation mechanisms of MGs. Full article
(This article belongs to the Special Issue Microstructure and Mechanical Properties of Metals and Alloys)
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