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Saksl K, Matvija M, Fujda M, Ballóková B, Varcholová D, Kubaško J, Möllmer J, Lange M, Podobová M. Zirconium-Modified Medium-Entropy Alloy (TiVNb) 85Cr 15 for Hydrogen Storage. Materials (Basel) 2024; 17:1732. [PMID: 38673089 PMCID: PMC11051122 DOI: 10.3390/ma17081732] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/08/2024] [Revised: 04/04/2024] [Accepted: 04/08/2024] [Indexed: 04/28/2024]
Abstract
In this study, we investigate the effect of small amounts of zirconium alloying the medium-entropy alloy (TiVNb)85Cr15, a promising material for hydrogen storage. Alloys with 1, 4, and 7 at.% of Zr were prepared by arc melting and found to be multiphase, comprising at least three phases, indicating that Zr addition does not stabilize a single-phase solid solution. The dominant BCC phase (HEA1) is the primary hydrogen absorber, while the minor phases HEA2 and HEA3 play a crucial role in hydrogen absorption/desorption. Among the studied alloys, Zr4 (TiVNb)81Cr15Zr4 shows the highest hydrogen storage capacity, ease of activation, and reversibly retrievable hydrogen. This alloy can absorb hydrogen at room temperature without additional processing, with a reversible capacity of up to 0.74 wt.%, corresponding to hydrogen-to-metal ratio H/M = 0.46. The study emphasizes the significant role of minor elemental additions in alloy properties, stressing the importance of tailored compositions for hydrogen storage applications. It suggests a direction for further research in metal hydride alloys for effective and safe hydrogen storage.
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Affiliation(s)
- Karel Saksl
- Faculty of Materials, Metallurgy and Recycling, Technical University of Košice, Letna 9, 042 00 Kosice, Slovakia; (M.M.); (M.F.); (D.V.); (J.K.)
- Institute of Materials Research, Slovak Academy of Sciences, Watsonova 47, 040 01 Kosice, Slovakia; (B.B.); (M.P.)
| | - Miloš Matvija
- Faculty of Materials, Metallurgy and Recycling, Technical University of Košice, Letna 9, 042 00 Kosice, Slovakia; (M.M.); (M.F.); (D.V.); (J.K.)
| | - Martin Fujda
- Faculty of Materials, Metallurgy and Recycling, Technical University of Košice, Letna 9, 042 00 Kosice, Slovakia; (M.M.); (M.F.); (D.V.); (J.K.)
| | - Beáta Ballóková
- Institute of Materials Research, Slovak Academy of Sciences, Watsonova 47, 040 01 Kosice, Slovakia; (B.B.); (M.P.)
| | - Dagmara Varcholová
- Faculty of Materials, Metallurgy and Recycling, Technical University of Košice, Letna 9, 042 00 Kosice, Slovakia; (M.M.); (M.F.); (D.V.); (J.K.)
- Institute of Materials Research, Slovak Academy of Sciences, Watsonova 47, 040 01 Kosice, Slovakia; (B.B.); (M.P.)
| | - Jakub Kubaško
- Faculty of Materials, Metallurgy and Recycling, Technical University of Košice, Letna 9, 042 00 Kosice, Slovakia; (M.M.); (M.F.); (D.V.); (J.K.)
| | - Jens Möllmer
- Institut für Nichtklassische Chemie e.V., Permoserstraße 15, 04318 Leipzig, Germany; (J.M.); (M.L.)
| | - Marcus Lange
- Institut für Nichtklassische Chemie e.V., Permoserstraße 15, 04318 Leipzig, Germany; (J.M.); (M.L.)
| | - Mária Podobová
- Institute of Materials Research, Slovak Academy of Sciences, Watsonova 47, 040 01 Kosice, Slovakia; (B.B.); (M.P.)
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Han X, Li X, Liao B, Zhang Y, Xu L, Guo X, Zhang S. The Effects of Heat Treatment on the Microstructure and Mechanical Properties of a Selective Laser Melted AlCoFeNi Medium-Entropy Alloy. Materials (Basel) 2024; 17:1582. [PMID: 38612096 PMCID: PMC11012990 DOI: 10.3390/ma17071582] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/23/2024] [Revised: 03/26/2024] [Accepted: 03/27/2024] [Indexed: 04/14/2024]
Abstract
A single body-centered cubic (BCC)-structured AlCoFeNi medium-entropy alloy (MEA) was prepared by the selective laser melting (SLM) technique. The hardness of the as-built sample was around 32.5 HRC. The ultimate tensile strength (UTS) was around 1211 MPa, the yield strength (YS) was around 1023 MPa, and the elongation (El) was around 10.8%. A novel BCC + B2 + face-centered cubic (FCC) structure was formed after aging. With an increase in aging temperature and duration, the number of fine grains increased, and more precipitates were observed. After aging at 450 °C for 4 h, the formed complex polyphase structure significantly improved the mechanical properties. Its hardness, UTS, YS, and El were around 45.7 HRC, 1535 MPa, 1489 MPa, and 8.5%, respectively. The improvement in mechanical properties was mainly due to Hall-Petch strengthening, which was caused by fine grains, and precipitation strengthening, which was caused by an increase in precipitates after aging. Meanwhile, the FCC precipitates made the alloy have good toughness. The complex interaction of multiple strengthening mechanisms leads to a good combination of strength, hardness, and toughness.
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Affiliation(s)
- Xinyang Han
- School of Physics and Materials Science, Guangzhou University, Guangzhou 510006, China
- Centre of Excellence for Advanced Materials, Dongguan 523808, China
| | - Xiangwei Li
- Centre of Excellence for Advanced Materials, Dongguan 523808, China
| | - Bokai Liao
- School of Chemistry and Chemical Engineering, Guangzhou University, Guangzhou 510006, China
| | - Youzhao Zhang
- Centre of Excellence for Advanced Materials, Dongguan 523808, China
| | - Lei Xu
- Robotics and Artificial Intelligence Division, Hong Kong Productivity Council, Kowloon, Hong Kong SAR 999077, China
| | - Xingpeng Guo
- School of Chemistry and Chemical Engineering, Guangzhou University, Guangzhou 510006, China
| | - Shuyan Zhang
- Centre of Excellence for Advanced Materials, Dongguan 523808, China
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Chu S, Zhang F, Chen D, Chen M, Liu P. Atomic-Scale In Situ Observations of Reversible Phase Transformation Assisted Twinning in a CrCoNi Medium-Entropy Alloy. Nano Lett 2024; 24:3624-3630. [PMID: 38421603 DOI: 10.1021/acs.nanolett.3c04516] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 03/02/2024]
Abstract
Twinning is an important deformation mode of face-centered-cubic (FCC) medium- and high-entropy alloys, especially under extreme loading conditions. However, the twinning mechanism in these alloys that have a low or even negative stacking fault energy remains debated. Here, we report atomic-scale in situ observations of the deformation process of a prototypical CrCoNi medium-entropy alloy under tension. We found that the parent FCC phase first transforms into a hexagonal close-packed (HCP) phase through Shockley partial dislocations slipping on the alternate {111} planes. Subsequently, the HCP phase rapidly changes to an FCC twin band. Such reversible phase transformation assisted twinning is greatly promoted by external tensile loads, as elucidated by geometric phase analysis. These results indicate the previously underestimated role of the metastable HCP phase in nanotwin nucleation and early plastic deformations of CrCoNi alloys and shed light on microstructure regulation of medium-entropy alloys with enhanced mechanical properties.
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Affiliation(s)
- Shufen Chu
- Shanghai Key Laboratory of Advanced High-temperature Materials and Precision Forming, State Key Laboratory of Metal Matrix Composites, School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, China
- Shanghai Jiao Tong University - JA Solar New Energy Materials Joint Research Center, Shanghai 200240, China
| | - Fan Zhang
- School of Materials Science and Engineering, Beijing Institute of Technology, Beijing 100081, China
| | - Dengke Chen
- Department of Engineering Mechanics, School of Naval Architecture, Ocean and Civil Engineering, Shanghai Jiao Tong University, Shanghai 200240, China
| | - Mingwei Chen
- Department of Materials Science and Engineering, Johns Hopkins University, Baltimore 21218, Maryland, United States
- Department of Materials Science and Engineering, College of Engineering, Southern University of Science and Technology, Shenzhen 518055, China
| | - Pan Liu
- Shanghai Key Laboratory of Advanced High-temperature Materials and Precision Forming, State Key Laboratory of Metal Matrix Composites, School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, China
- Shanghai Jiao Tong University - JA Solar New Energy Materials Joint Research Center, Shanghai 200240, China
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Wong KK, Hsu HC, Wu SC, Ho WF. A Review: Design from Beta Titanium Alloys to Medium-Entropy Alloys for Biomedical Applications. Materials (Basel) 2023; 16:7046. [PMID: 37959643 PMCID: PMC10650816 DOI: 10.3390/ma16217046] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/13/2023] [Revised: 10/29/2023] [Accepted: 11/03/2023] [Indexed: 11/15/2023]
Abstract
β-Ti alloys have long been investigated and applied in the biomedical field due to their exceptional mechanical properties, ductility, and corrosion resistance. Metastable β-Ti alloys have garnered interest in the realm of biomaterials owing to their notably low elastic modulus. Nevertheless, the inherent correlation between a low elastic modulus and relatively reduced strength persists, even in the case of metastable β-Ti alloys. Enhancing the strength of alloys contributes to improving their fatigue resistance, thereby preventing an implant material from failure in clinical usage. Recently, a series of biomedical high-entropy and medium-entropy alloys, composed of biocompatible elements such as Ti, Zr, Nb, Ta, and Mo, have been developed. Leveraging the contributions of the four core effects of high-entropy alloys, both biomedical high-entropy and medium-entropy alloys exhibit excellent mechanical strength, corrosion resistance, and biocompatibility, albeit accompanied by an elevated elastic modulus. To satisfy the demands of biomedical implants, researchers have sought to synthesize the strengths of high-entropy alloys and metastable β-Ti alloys, culminating in the development of metastable high-entropy/medium-entropy alloys that manifest both high strength and a low elastic modulus. Consequently, the design principles for new-generation biomedical medium-entropy alloys and conventional metastable β-Ti alloys can be converged. This review focuses on the design from β-Ti alloys to the novel metastable medium-entropy alloys for biomedical applications.
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Affiliation(s)
- Ka-Kin Wong
- Department of Chemical and Materials Engineering, National University of Kaohsiung, Kaohsiung 81148, Taiwan;
| | - Hsueh-Chuan Hsu
- Department of Dental Technology and Materials Science, Central Taiwan University of Science and Technology, Taichung 40601, Taiwan; (H.-C.H.); (S.-C.W.)
| | - Shih-Ching Wu
- Department of Dental Technology and Materials Science, Central Taiwan University of Science and Technology, Taichung 40601, Taiwan; (H.-C.H.); (S.-C.W.)
| | - Wen-Fu Ho
- Department of Chemical and Materials Engineering, National University of Kaohsiung, Kaohsiung 81148, Taiwan;
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Okulov A, Korobov Y, Stepchenkov A, Makarov A, Iusupova O, Korkh Y, Kuznetsova T, Kharanzhevskiy E, Liu K. Mechanical and Structural Characterization of Laser-Cladded Medium-Entropy FeNiCr-B 4C Coatings. Materials (Basel) 2023; 16:5479. [PMID: 37570183 PMCID: PMC10419838 DOI: 10.3390/ma16155479] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/23/2023] [Revised: 06/28/2023] [Accepted: 07/01/2023] [Indexed: 08/13/2023]
Abstract
Equiatomic medium-entropy alloy (MEA) FeNiCr-B4C (0, 1, and 3 wt.% B4C) coatings were deposited onto an AISI 1040 steel substrate using pulsed laser cladding. Based on an SEM microstructural analysis, it was found that the cross-sections of all the obtained specimens were characterized by an average coating thickness of 400 ± 20 μm, a sufficiently narrow (100 ± 20 μm) "coating-substrate" transition zone, and the presence of a small number of defects, including cracks and pores. An XRD analysis showed that the formed coatings consisted of a single face-centered cubic (FCC) γ-phase and the space group Fm-3m, regardless of the B4C content. However, additional TEM analysis of the FeNiCr coating with 3 wt.% B4C revealed a two-phase FCC structure consisting of grains (FCC-1 phase, Fm-3m) up to 1 µm in size and banded interlayers (FCC-2 phase, Fm-3m) between the grains. The grains were clean with a low density of dislocations. Raman spectroscopy confirmed the presence of B4C carbides inside the FeNiCr (1 and 3 wt.% B4C) coatings, as evidenced by detected peaks corresponding to amorphous carbon and peaks indicating the stretching of C-B-C chains. The mechanical characterization of the FeNiCr-B4C coatings specified that additions of 1 and 3 wt.% B4C resulted in a notable increase in microhardness of 16% and 38%, respectively, with a slight decrease in ductility of 4% and 10%, respectively, compared to the B4C-free FeNiCr coating. Thus, the B4C addition can be considered a promising method for strengthening laser-cladded MEA FeNiCr-B4C coatings.
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Affiliation(s)
- Artem Okulov
- M.N. Mikheev Institute of Metal Physics, Ural Branch of the Russian Academy of Sciences, 620108 Ekaterinburg, Russia
| | - Yury Korobov
- M.N. Mikheev Institute of Metal Physics, Ural Branch of the Russian Academy of Sciences, 620108 Ekaterinburg, Russia
| | - Alexander Stepchenkov
- M.N. Mikheev Institute of Metal Physics, Ural Branch of the Russian Academy of Sciences, 620108 Ekaterinburg, Russia
| | - Aleksey Makarov
- M.N. Mikheev Institute of Metal Physics, Ural Branch of the Russian Academy of Sciences, 620108 Ekaterinburg, Russia
| | - Olga Iusupova
- M.N. Mikheev Institute of Metal Physics, Ural Branch of the Russian Academy of Sciences, 620108 Ekaterinburg, Russia
| | - Yulia Korkh
- M.N. Mikheev Institute of Metal Physics, Ural Branch of the Russian Academy of Sciences, 620108 Ekaterinburg, Russia
| | - Tatyana Kuznetsova
- M.N. Mikheev Institute of Metal Physics, Ural Branch of the Russian Academy of Sciences, 620108 Ekaterinburg, Russia
- Department of Physics, Ural Federal University, 620002 Ekaterinburg, Russia
| | | | - Kun Liu
- School of Materials Science and Engineering, Jiangsu University of Science and Technology, Zhenjiang 212100, China
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Shen R, Ni Z, Peng S, Yan H, Tian Y. Effects of V Addition on the Deformation Mechanism and Mechanical Properties of Non-Equiatomic CoCrNi Medium-Entropy Alloys. Materials (Basel) 2023; 16:5167. [PMID: 37512441 PMCID: PMC10385466 DOI: 10.3390/ma16145167] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/09/2023] [Revised: 07/20/2023] [Accepted: 07/21/2023] [Indexed: 07/30/2023]
Abstract
Equiatomic CoCrNi medium-entropy alloys exhibit superior strength and ductility. In this work, a non-equiatomic CoCrNi alloy with low stacking fault energy was designed, and different fractions of V were added to control the stacking fault energy and lattice distortion. Mechanical properties were evaluated by tensile tests, and deformation microstructures were characterized by transmission electron microscope (TEM). The main deformation mechanisms of CoCrNiV alloy with low V content are dislocation slip, stacking faults, and deformation-induced HCP phase transformation, while the dominant deformation patterns of CoCrNiV alloy with high V contents are dislocation slip and stacking faults. The yield strength increases dramatically when the V content is high, and the strain-hardening behavior changes non-monotonically with increasing the V content. V addition increases the stacking fault energy (SFE) and lattice distortion. The lower strain-hardening rate of 6V alloy than that of 2V alloy is dominated by the SFE. The higher strain-hardening rate of 10V alloy than that of 6V alloy is dominated by the lattice distortion. The effects of V addition on the SFE, lattice distortion, and strain-hardening behavior are discussed.
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Affiliation(s)
- Rui Shen
- Key Laboratory for Anisotropy and Texture of Materials (Ministry of Education), School of Materials Science and Engineering, Northeastern University, Shenyang 110819, China
| | - Zengyu Ni
- Key Laboratory for Anisotropy and Texture of Materials (Ministry of Education), School of Materials Science and Engineering, Northeastern University, Shenyang 110819, China
| | - Siyuan Peng
- Key Laboratory for Anisotropy and Texture of Materials (Ministry of Education), School of Materials Science and Engineering, Northeastern University, Shenyang 110819, China
| | - Haile Yan
- Key Laboratory for Anisotropy and Texture of Materials (Ministry of Education), School of Materials Science and Engineering, Northeastern University, Shenyang 110819, China
| | - Yanzhong Tian
- Key Laboratory for Anisotropy and Texture of Materials (Ministry of Education), School of Materials Science and Engineering, Northeastern University, Shenyang 110819, China
- Research Center for Metallic Wires, Northeastern University, Shenyang 110819, China
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Lee U, Bae JW. Microstructural Changes and Mechanical Properties of Precipitation-Strengthened Medium-Entropy Fe 71.25(CoCrMnNi) 23.75Cu 3Al 2 Maraging Alloy. Materials (Basel) 2023; 16:ma16093589. [PMID: 37176469 PMCID: PMC10180304 DOI: 10.3390/ma16093589] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/20/2023] [Revised: 04/30/2023] [Accepted: 05/04/2023] [Indexed: 05/15/2023]
Abstract
Metal alloys with enhanced mechanical properties are in considerable demand in various industries. Thus, this study focused on the development of nanosized precipitates in Fe71.25(CoCrMnNi)23.75Cu3Al2 maraging medium-entropy alloy (MEA). The Fe-based alloying design in the MEA samples initially formed a body-centered cubic (BCC) lath martensite structure. After a subsequent annealing process at 450 °C for varying durations (1, 3, 5, and 7 h), nanosized precipitates (B2 intermetallic) enriched with Cu and with a diameter of approximately 5 nm formed, significantly increasing the hardness of the alloy. The highest Vickers microhardness of 597 HV, along with compressive yield strength and ultimate compressive strength of 2079 MPa and 2843 MPa, respectively, was achieved for the Aged_7h sample. Therefore, the BCC lath martensite structure with B2 intermetallics leads to remarkable mechanical properties.
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Affiliation(s)
- Unhae Lee
- POSCO Technical Research Laboratories, Gwangyang 57807, Republic of Korea
- BISTEP Evaluation & Analysis of Regional Innovation Program Division, Busan 48058, Republic of Korea
| | - Jae Wung Bae
- Department of Metallurgical Engineering, Pukyong National University, Busan 48513, Republic of Korea
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Liu J, Zhao Y, Hu R, Zhang M, Ding Y. Effects of Cu and Ag Elements on Corrosion Resistance of Dual-Phase Fe-Based Medium-Entropy Alloys. Materials (Basel) 2023; 16:3243. [PMID: 37110079 PMCID: PMC10144962 DOI: 10.3390/ma16083243] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 03/20/2023] [Revised: 04/15/2023] [Accepted: 04/18/2023] [Indexed: 06/19/2023]
Abstract
The effect of adding elements to promote phase separation on the functional properties of medium-entropy alloys has rarely been reported. In this paper, medium-entropy alloys with dual FCC phases were prepared by adding Cu and Ag elements, which exhibited a positive mixing enthalpy with Fe. Dual-phase Fe-based medium-entropy alloys were fabricated via water-cooled copper crucible magnetic levitation melting and copper mold suction casting. The effects of Cu and Ag elements microalloying on the microstructure and corrosion resistance of a medium-entropy alloy were studied, and an optimal composition was defined. The results show that Cu and Ag elements were enriched between the dendrites and precipitated an FCC2 phase on the FCC1 matrix. During electrochemical corrosion under PBS solutions, Cu and Ag elements formed an oxide layer on the alloy's surface, which prevented the matrix atoms from diffusing. With an increase in Cu and Ag content, the corrosion potential and the arc radius of capacitive resistance increased, while the corrosion current density decreased, indicating that corrosion resistance improved. The corrosion current density of (Fe63.3Mn14Si9.1Cr9.8C3.8)94Cu3Ag3 in PBS solution was as high as 1.357 × 10-8 A·cm-2.
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Affiliation(s)
- Jianjun Liu
- State Key Laboratory of Advanced Processing and Recycling of Non-Ferrous Metals, Lanzhou University of Technology, Lanzhou 730050, China
- Wenzhou Pump and Valve Engineering Research Institute, Lanzhou University of Technology, Wenzhou 325105, China
| | - Yanchun Zhao
- State Key Laboratory of Advanced Processing and Recycling of Non-Ferrous Metals, Lanzhou University of Technology, Lanzhou 730050, China
- Wenzhou Pump and Valve Engineering Research Institute, Lanzhou University of Technology, Wenzhou 325105, China
| | - Ruonan Hu
- State Key Laboratory of Advanced Processing and Recycling of Non-Ferrous Metals, Lanzhou University of Technology, Lanzhou 730050, China
| | - Minya Zhang
- State Key Laboratory of Advanced Processing and Recycling of Non-Ferrous Metals, Lanzhou University of Technology, Lanzhou 730050, China
| | - Yutian Ding
- State Key Laboratory of Advanced Processing and Recycling of Non-Ferrous Metals, Lanzhou University of Technology, Lanzhou 730050, China
- Wenzhou Pump and Valve Engineering Research Institute, Lanzhou University of Technology, Wenzhou 325105, China
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Povolyaeva E, Shaysultanov D, Astakhov I, Evlashin S, Klimova M, Stepanov N, Zherebtsov S. Mechanical Behavior of a Medium-Entropy Fe 65(CoNi) 25Cr 9.5C 0.5 Alloy Produced by Selective Laser Melting. Materials (Basel) 2023; 16:3193. [PMID: 37110032 PMCID: PMC10145717 DOI: 10.3390/ma16083193] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 03/10/2023] [Revised: 04/10/2023] [Accepted: 04/15/2023] [Indexed: 06/19/2023]
Abstract
Specimens of a medium-entropy Fe65(CoNi)25Cr9.5C0.5 (in at.%) alloy were produced using additive manufacturing (selective laser melting, SLM). The selected parameters of SLM resulted in a very high density in the specimens with a residual porosity of less than 0.5%. The structure and mechanical behavior of the alloy were studied under tension at room and cryogenic temperatures. The microstructure of the alloy produced by SLM comprised an elongated substructure, inside which cells with a size of ~300 nm were observed. The as-produced alloy demonstrated high yield strength and ultimate tensile strength (YS = 680 MPa; UTS = 1800 MPa) along with good ductility (tensile elongation = 26%) at a cryogenic temperature (77 K) that was associated with the development of transformation-induced plasticity (TRIP) effect. At room temperature, the TRIP effect was less pronounced. Consequently, the alloy demonstrated lower strain hardening and a YS/UTS of 560/640 MPa. The deformation mechanisms of the alloy are discussed.
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Affiliation(s)
- Elizaveta Povolyaeva
- Laboratory of Bulk Nanostructured Materials, Belgorod National Research University, 85 Pobeda Str., 308015 Belgorod, Russia
| | - Dmitry Shaysultanov
- Laboratory of Bulk Nanostructured Materials, Belgorod National Research University, 85 Pobeda Str., 308015 Belgorod, Russia
| | - Ilya Astakhov
- Laboratory of Bulk Nanostructured Materials, Belgorod National Research University, 85 Pobeda Str., 308015 Belgorod, Russia
| | - Stanislav Evlashin
- Skolkovo Innovation Center, 5 Str. Nobel, 121205 Moscow, Russia
- World-Class Research Center “Advanced Digital Technologies”, State Marine Technical University, 198095 Saint Petersburg, Russia
| | - Margarita Klimova
- Laboratory of Bulk Nanostructured Materials, Belgorod National Research University, 85 Pobeda Str., 308015 Belgorod, Russia
| | - Nikita Stepanov
- Laboratory of Bulk Nanostructured Materials, Belgorod National Research University, 85 Pobeda Str., 308015 Belgorod, Russia
- World-Class Research Center “Advanced Digital Technologies”, State Marine Technical University, 198095 Saint Petersburg, Russia
| | - Sergey Zherebtsov
- Laboratory of Bulk Nanostructured Materials, Belgorod National Research University, 85 Pobeda Str., 308015 Belgorod, Russia
- World-Class Research Center “Advanced Digital Technologies”, State Marine Technical University, 198095 Saint Petersburg, Russia
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Zhang Z, Su Z, Zhang B, Yu Q, Ding J, Shi T, Lu C, Ritchie RO, Ma E. Effect of local chemical order on the irradiation-induced defect evolution in CrCoNi medium-entropy alloy. Proc Natl Acad Sci U S A 2023; 120:e2218673120. [PMID: 37014854 PMCID: PMC10104586 DOI: 10.1073/pnas.2218673120] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2022] [Accepted: 02/27/2023] [Indexed: 04/05/2023] Open
Abstract
High- (and medium-) entropy alloys have emerged as potentially suitable structural materials for nuclear applications, particularly as they appear to show promising irradiation resistance. Recent studies have provided evidence of the presence of local chemical order (LCO) as a salient feature of these complex concentrated solid-solution alloys. However, the influence of such LCO on their irradiation response has remained uncertain thus far. In this work, we combine ion irradiation experiments with large-scale atomistic simulations to reveal that the presence of chemical short-range order, developed as an early stage of LCO, slows down the formation and evolution of point defects in the equiatomic medium-entropy alloy CrCoNi during irradiation. In particular, the irradiation-induced vacancies and interstitials exhibit a smaller difference in their mobility, arising from a stronger effect of LCO in localizing interstitial diffusion. This effect promotes their recombination as the LCO serves to tune the migration energy barriers of these point defects, thereby delaying the initiation of damage. These findings imply that local chemical ordering may provide a variable in the design space to enhance the resistance of multi-principal element alloys to irradiation damage.
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Affiliation(s)
- Zhen Zhang
- Center for Alloy Innovation and Design, State Key Laboratory for Mechanical Behavior of Materials, Xi’an Jiaotong University, Xi’an 710049, China
| | - Zhengxiong Su
- School of Nuclear Science and Technology, Xi’an Jiaotong University, Xi’an710049, China
| | - Bozhao Zhang
- Center for Alloy Innovation and Design, State Key Laboratory for Mechanical Behavior of Materials, Xi’an Jiaotong University, Xi’an 710049, China
| | - Qin Yu
- Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA94720
| | - Jun Ding
- Center for Alloy Innovation and Design, State Key Laboratory for Mechanical Behavior of Materials, Xi’an Jiaotong University, Xi’an 710049, China
| | - Tan Shi
- School of Nuclear Science and Technology, Xi’an Jiaotong University, Xi’an710049, China
| | - Chenyang Lu
- School of Nuclear Science and Technology, Xi’an Jiaotong University, Xi’an710049, China
| | - Robert O. Ritchie
- Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA94720
- Department of Materials Science and Engineering, University of California, Berkeley, CA94720
| | - Evan Ma
- Center for Alloy Innovation and Design, State Key Laboratory for Mechanical Behavior of Materials, Xi’an Jiaotong University, Xi’an 710049, China
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Chang YC, Lin K, Ma JL, Huang HF, Chang SH, Lin HC. Improvement of Corrosion and Wear Resistance of CoCrNiSi 0.3 Medium-Entropy Alloy by Sputtering CrN Film. Materials (Basel) 2023; 16:1482. [PMID: 36837112 PMCID: PMC9959495 DOI: 10.3390/ma16041482] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 12/19/2022] [Revised: 01/25/2023] [Accepted: 02/07/2023] [Indexed: 06/18/2023]
Abstract
In this study, Co, Cr, and Ni were selected as the equal-atomic medium entropy alloy (MEA) systems, and Si was added to form CoCrNiSi0.3 MEA. In order to further improve its wear and corrosion properties, CrN film was sputtered on the surface. In addition, to enhance the adhesion between the soft CoCrNiSi0.3 substrate and the super-hard CrN film, a Cr buffer layer was pre-sputtered on the CoCrNiSi0.3 substrate. The experimental results show that the CrN film exhibits a columnar grain structure, and the film growth rate is about 2.022 μm/h. With the increase of sputtering time, the increase in CrN film thickness, and the refinement of columnar grains, the wear and corrosion resistance improves. Among all CoCrNiSi0.3 MEAs without and with CrN films prepared in this study, the CoCrNiSi0.3 MEA with 3 h-sputtered CrN film has the lowest wear rate of 2.249 × 10-5 mm3·m-1·N-1, and the best corrosion resistance of Icorr 19.37 μA·cm-2 and Rp 705.85 Ω·cm2.
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Affiliation(s)
- Yi-Chun Chang
- Department of Materials Science and Engineering, National Taiwan University, Taipei 10617, Taiwan
| | - Kaifan Lin
- Department of Materials Science and Engineering, National Taiwan University, Taipei 10617, Taiwan
| | - Ju-Lung Ma
- Department of Materials Science and Engineering, National Taiwan University, Taipei 10617, Taiwan
| | - Han-Fu Huang
- Department of Materials and Mineral Resources Engineering, National Taipei University of Technology, Taipei 10608, Taiwan
| | - Shih-Hsien Chang
- Department of Materials and Mineral Resources Engineering, National Taipei University of Technology, Taipei 10608, Taiwan
| | - Hsin-Chih Lin
- Department of Materials Science and Engineering, National Taiwan University, Taipei 10617, Taiwan
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12
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Wong KK, Hsu HC, Wu SC, Hung TL, Ho WF. Structure, Properties, and Corrosion Behavior of Ti-Rich TiZrNbTa Medium-Entropy Alloys with β+α″+α' for Biomedical Application. Materials (Basel) 2022; 15:7953. [PMID: 36431438 PMCID: PMC9696250 DOI: 10.3390/ma15227953] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 10/17/2022] [Revised: 11/07/2022] [Accepted: 11/09/2022] [Indexed: 06/16/2023]
Abstract
Five Ti-rich β+α″+α′ Ti−Zr−Nb−Ta biomedical medium-entropy alloys with excellent mechanical properties and corrosion resistance were developed by considering thermodynamic parameters and using the valence electron concentration formula. The results of this study demonstrated that the traditional valence electron concentration formula for predicting phases is not entirely applicable to medium-entropy alloys. All solution-treated samples with homogeneous compositions were obtained at a low temperature (900 °C) and within a short period (20 min). All solution-treated samples exhibited low elastic moduli ranging from 49 to 57 GPa, which were significantly lower than those of high-entropy alloys with β phase. Solution-treated Ti65−Zr29−Nb3−Ta3 exhibited an ultra-high bending strength (1102 MPa), an elastic recovery angle (>30°), and an ultra-low elastic modulus (49 GPa), which are attributed to its α″ volume fraction as high as more than 60%. The pitting potentials of all samples were higher than 1.8 V, and their corrosion current densities were lower than 10−5 A/cm3 in artificially simulated body fluid at 37 °C. The surface oxide layers on Ti65−Zr29−Nb3−Ta3 comprised TiO2, ZrO2, Nb2O5, and Ta2O5 (as discovered through X-ray photoelectron spectroscopy) and provided the alloy with excellent corrosion and pitting resistance.
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Affiliation(s)
- Ka-Kin Wong
- Department of Chemical and Materials Engineering, National University of Kaohsiung, Kaohsiung 81148, Taiwan
| | - Hsueh-Chuan Hsu
- Department of Dental Technology and Materials Science, Central Taiwan University of Science and Technology, Taichung 40601, Taiwan
| | - Shih-Ching Wu
- Department of Dental Technology and Materials Science, Central Taiwan University of Science and Technology, Taichung 40601, Taiwan
| | - Tun-Li Hung
- Department of Chemical and Materials Engineering, National University of Kaohsiung, Kaohsiung 81148, Taiwan
| | - Wen-Fu Ho
- Department of Chemical and Materials Engineering, National University of Kaohsiung, Kaohsiung 81148, Taiwan
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13
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Kwon H, Harjo S, Kawasaki T, Gong W, Jeong SG, Kim ES, Sathiyamoorthi P, Kato H, Kim HS. Work hardening behavior of hot-rolled metastable Fe 50Co 25Ni 10Al 5Ti 5Mo 5 medium-entropy alloy: in situ neutron diffraction analysis. Sci Technol Adv Mater 2022; 23:579-586. [PMID: 36212683 PMCID: PMC9542855 DOI: 10.1080/14686996.2022.2122868] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/17/2022] [Revised: 08/28/2022] [Accepted: 08/31/2022] [Indexed: 06/12/2023]
Abstract
Metastability engineering is a strategy to enhance the strength and ductility of alloys via deliberately lowering phase stability and prompting deformation-induced martensitic transformation. The advantages of the strategy are widely exploited by ferrous medium-entropy alloys (MEAs) that exhibit phase transformation from metastable face-centered cubic (FCC) to hexagonal close-packed (HCP) or body-centered cubic (BCC) martensite and a significant increase in work hardening. Fe50Co25Ni10Al5Ti5Mo5 (at%) MEA is an example of such materials, which shows ~1.5 GPa of tensile strength assisted by exceptional work hardening from the deformation-induced BCC martensitic transformation. In this work, the martensitic transformation and its effect on the mechanical response of the MEA were studied by in situ neutron diffraction under tensile loading. Strain-induced BCC martensite started forming rapidly from the beginning of plastic deformation, reaching a phase fraction of ~100% when deformed to ~10% of true strain. Lattice strain and phase stress evolution indicate that stress was dynamically partitioned onto the newly formed BCC martensite, which is responsible for the work hardening response and high flow stress of the MEA. This work shows how great a role FCC to BCC martensitic transformation can play in enhancing the mechanical properties of ferrous MEAs.
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Affiliation(s)
- Hyeonseok Kwon
- Department of Materials Science and Engineering, Pohang University of Science and Technology (POSTECH), Pohang, Republic of Korea
| | - Stefanus Harjo
- J-PARC Center, Japan Atomic Energy Agency, Ibaraki, Japan
| | | | - Wu Gong
- J-PARC Center, Japan Atomic Energy Agency, Ibaraki, Japan
| | - Sang Guk Jeong
- Department of Materials Science and Engineering, Pohang University of Science and Technology (POSTECH), Pohang, Republic of Korea
| | - Eun Seong Kim
- Department of Materials Science and Engineering, Pohang University of Science and Technology (POSTECH), Pohang, Republic of Korea
| | - Praveen Sathiyamoorthi
- Department of Metallurgical Engineering, Indian Institute of Technology (BHU), Varanasi, India
| | - Hidemi Kato
- Institute for Materials Research, Tohoku University, Sendai, Japan
| | - Hyoung Seop Kim
- Department of Materials Science and Engineering, Pohang University of Science and Technology (POSTECH), Pohang, Republic of Korea
- Institute for Materials Research, Tohoku University, Sendai, Japan
- Center for Heterogenic Metal Additive Manufacturing, Pohang University of Science and Technology (POSTECH), Pohang, Republic of Korea
- Graduate Institute of Ferrous and Energy materials Technology (GIFT), Pohang University of Science and Technology (POSTECH), Pohang, Republic of Korea
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14
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Chen PS, Shiu SJ, Tsai PH, Liao YC, Jang JSC, Wu HJ, Chang SY, Chen CY, Tsao IY. Remarkable Enhanced Mechanical Properties of TiAlCrNbV Medium-Entropy Alloy with Zr Additions. Materials (Basel) 2022; 15:6324. [PMID: 36143635 PMCID: PMC9506522 DOI: 10.3390/ma15186324] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 08/05/2022] [Revised: 09/06/2022] [Accepted: 09/08/2022] [Indexed: 06/16/2023]
Abstract
Most medium entropy alloys (MEAs) exhibit excellent mechanical properties, but their applications are limited because of their high density. This study explores a series of lightweight nonequiatomic Ti65(AlCrNbV)35-xZrx (x = 3, 5, 7, and 10) MEAs with a low density, high strength, and high ductility. To achieve solid solution strengthening, Zr with a large atomic radius was used. In addition, various thermomechanical treatment parameters were adopted to further improve the MEAs’ mechanical properties. The density of the MEAs was revealed to be approximately 5 g/cm3, indicating that they were lightweight. Through an X-ray diffraction analysis, the MEAs were revealed to have a single body-centered cubic structure not only in the as-cast state but also after thermomechanical treatment. In terms of mechanical properties, all the as-cast MEAs with Zr additions achieved excellent performance (>1000 MPa tensile yield strength and 20% tensile ductility). In addition, hot rolling effectively eliminated the defects of the MEAs; under a given yield strength, hot-rolled MEAs exhibited superior ductility relative to non-hot-rolled MEAs. Overall, the Ti65(AlCrNbV)28Zr7 MEAs exhibited an optimum combination of mechanical properties (yield strength > 1200 MPa, plastic strain > 15%) after undergoing hot rolling 50%, cold rolling 70%, and rapid annealing for 30 to 50 s (at a temperature of approximately 850 °C) with a heating rate of 15 K/s. With their extremely high specific yield strength (264 MPa·g/cm3) and high ductility (22%), the Ti65(AlCrNbV)28Zr7 MEAs demonstrate considerable potential for energy and transportation applications.
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Affiliation(s)
- Po-Sung Chen
- Institute of Materials Science and Engineering, National Central University, Zhongli 320, Taiwan
| | - Sheng-Jia Shiu
- Institute of Materials Science and Engineering, National Central University, Zhongli 320, Taiwan
| | - Pei-Hua Tsai
- Institute of Materials Science and Engineering, National Central University, Zhongli 320, Taiwan
| | - Yu-Chin Liao
- Department of Mechanical Engineering, National Central University, Zhongli 320, Taiwan
| | - Jason Shian-Ching Jang
- Institute of Materials Science and Engineering, National Central University, Zhongli 320, Taiwan
- Department of Mechanical Engineering, National Central University, Zhongli 320, Taiwan
| | - Hsin-Jay Wu
- Department of Materials Science and Engineering, National Yang Ming Chiao Tung University, Hsinchu 300, Taiwan
| | - Shou-Yi Chang
- Department of Materials Science and Engineering, National Tsing Hua University, Hsinchu 300, Taiwan
| | - Chih-Yen Chen
- Department of Materials and Optoelectronic Science, National Sun Yat-sen University, Kaohsiung 804, Taiwan
| | - I-Yu Tsao
- Institute of Materials Science and Engineering, National Central University, Zhongli 320, Taiwan
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Shen X, Liu C, Wang B, Zhang Y, Su G, Li A. Surface Properties of Medium-Entropy Alloy Coatings Prepared through a Combined Process of Laser Cladding and Ultrasonic Burnishing. Materials (Basel) 2022; 15:5576. [PMID: 36013712 PMCID: PMC9416578 DOI: 10.3390/ma15165576] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 07/29/2022] [Revised: 08/11/2022] [Accepted: 08/11/2022] [Indexed: 06/15/2023]
Abstract
The preparation of functional coatings on metal substrates is an effective method to enhance the surface of steel structures with good serviceability in applications for engineering parts. The objective of this research is to analyze the surface properties of two sorts of medium-entropy alloy (MEA) coatings prepared by laser cladding. After cladding, the two prepared coatings were strengthened by ultrasonic burnishing (UB) treatment. Cladding coating samples before and after being UB-treated were comparatively tested in order to investigate the process effects of UB. When compared with corresponding untreated coating samples, the roughness values of the two sorts of UB-treated samples were decreased by 88.7% and 87.6%, the porosities were decreased by 63.8% and 73.4%, and the micro-hardness values were increased by 41.7% and 32.7%, respectively. Furthermore, the two sorts of UB-treated coating samples exhibited better mechanical properties and wear resistance than corresponding untreated samples.
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Affiliation(s)
- Xuehui Shen
- School of Mechanical Engineering, Qilu University of Technology (Shandong Academy of Sciences), Jinan 250353, China
- Shandong Institute of Mechanical Design and Research, Jinan 250031, China
| | - Chang Liu
- School of Mechanical Engineering, Qilu University of Technology (Shandong Academy of Sciences), Jinan 250353, China
- Shandong Institute of Mechanical Design and Research, Jinan 250031, China
| | - Baolin Wang
- School of Mechanical Engineering, Qilu University of Technology (Shandong Academy of Sciences), Jinan 250353, China
- Shandong Institute of Mechanical Design and Research, Jinan 250031, China
| | - Yu Zhang
- School of Mechanical Engineering, Qilu University of Technology (Shandong Academy of Sciences), Jinan 250353, China
- Shandong Institute of Mechanical Design and Research, Jinan 250031, China
| | - Guosheng Su
- School of Mechanical Engineering, Qilu University of Technology (Shandong Academy of Sciences), Jinan 250353, China
- Shandong Institute of Mechanical Design and Research, Jinan 250031, China
| | - Anhai Li
- Key Laboratory of High Efficiency and Clean Mechanical Manufacture of MOE, School of Mechanical Engineering, Shandong University, Jinan 250061, China
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Chen PS, Liao YC, Lin YT, Tsai PH, Jang JSC, Hsieh KC, Chen CY, Huang JC, Wu HJ, Tsao IY. Development of Novel Lightweight Al-Rich Quinary Medium-Entropy Alloys with High Strength and Ductility. Materials (Basel) 2021; 14:4223. [PMID: 34361417 DOI: 10.3390/ma14154223] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/15/2021] [Revised: 07/20/2021] [Accepted: 07/26/2021] [Indexed: 11/25/2022]
Abstract
Most high-entropy alloys and medium-entropy alloys (MEAs) possess outstanding mechanical properties. In this study, a series of lightweight nonequiatomic Al50–Ti–Cr–Mn–V MEAs with a dual phase were produced through arc melting and drop casting. These cast alloys were composed of body-centered cubic and face-centered cubic phases. The density of all investigated MEAs was less than 5 g/cm3 in order to meet energy and transportation industry requirements. The effect of each element on the microstructure evolution and mechanical properties of these MEAs was investigated. All the MEAs demonstrated outstanding compressive strength, with no fractures observed after a compressive strain of 20%. Following the fine-tuning of the alloy composition, the Al50Ti20Cr10Mn15V5 MEA exhibited the most compressive strength (~1800 MPa) and ductility (~34%). A significant improvement in the mechanical compressive properties was achieved (strength of ~2000 MPa, strain of ~40%) after annealing (at 1000 °C for 0.5 h) and oil-quenching. With its extremely high specific compressive strength (452 MPa·g/cm3) and ductility, the lightweight Al50Ti20Cr10Mn15V5 MEA demonstrates good potential for energy or transportation applications in the future.
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Liao YC, Chen PS, Li CH, Tsai PH, Jang JSC, Hsieh KC, Chen CY, Lin PH, Huang JC, Wu HJ, Lo YC, Huang CW, Tsao IY. Development of Novel Lightweight Dual-Phase Al-Ti-Cr-Mn-V Medium-Entropy Alloys with High Strength and Ductility. Entropy (Basel) 2020; 22:E74. [PMID: 33285849 DOI: 10.3390/e22010074] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/29/2019] [Revised: 12/23/2019] [Accepted: 01/04/2020] [Indexed: 11/25/2022]
Abstract
A novel lightweight Al-Ti-Cr-Mn-V medium-entropy alloy (MEA) system was developed using a nonequiatiomic approach and alloys were produced through arc melting and drop casting. These alloys comprised a body-centered cubic (BCC) and face-centered cubic (FCC) dual phase with a density of approximately 4.5 g/cm3. However, the fraction of the BCC phase and morphology of the FCC phase can be controlled by incorporating other elements. The results of compression tests indicated that these Al-Ti-Cr-Mn-V alloys exhibited a prominent compression strength (~1940 MPa) and ductility (~30%). Moreover, homogenized samples maintained a high compression strength of 1900 MPa and similar ductility (30%). Due to the high specific compressive strength (0.433 GPa·g/cm3) and excellent combination of strength and ductility, the cast lightweight Al-Ti-Cr-Mn-V MEAs are a promising alloy system for application in transportation and energy industries.
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Yang M, Yan D, Yuan F, Jiang P, Ma E, Wu X. Dynamically reinforced heterogeneous grain structure prolongs ductility in a medium-entropy alloy with gigapascal yield strength. Proc Natl Acad Sci U S A 2018; 115:7224-9. [PMID: 29946032 DOI: 10.1073/pnas.1807817115] [Citation(s) in RCA: 226] [Impact Index Per Article: 37.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Back stress hardening is usually not obvious in single-phase homogeneous grains, but can be made unusually large and sustained to large tensile strains by creating an unusually heterogeneous grain structure in single-phase alloys with low stacking fault energy (SFE), as demonstrated here for the face-centered cubic CrCoNi medium-entropy alloy. The low SFE facilitates the generation of twinned nanograins and stacking faults during tensile straining, dynamically reinforcing the heterogeneity. Large uniform tensile strain can be achieved after yielding even at gigapascal stress, in the absence of heterogeneities from any second phase. Ductility, i.e., uniform strain achievable in uniaxial tension, diminishes for materials with very high yield strength. Even for the CrCoNi medium-entropy alloy (MEA), which has a simple face-centered cubic (FCC) structure that would bode well for high ductility, the fine grains processed to achieve gigapascal strength exhaust the strain hardening ability such that, after yielding, the uniform tensile strain is as low as ∼2%. Here we purposely deploy, in this MEA, a three-level heterogeneous grain structure (HGS) with grain sizes spanning the nanometer to micrometer range, imparting a high yield strength well in excess of 1 GPa. This heterogeneity results from this alloy’s low stacking fault energy, which facilitates corner twins in recrystallization and stores deformation twins and stacking faults during tensile straining. After yielding, the elastoplastic transition through load transfer and strain partitioning among grains of different sizes leads to an upturn of the strain hardening rate, and, upon further tensile straining at room temperature, corner twins evolve into nanograins. This dynamically reinforced HGS leads to a sustainable strain hardening rate, a record-wide hysteresis loop in load−unload−reload stress−strain curve and hence high back stresses, and, consequently, a uniform tensile strain of 22%. As such, this HGS achieves, in a single-phase FCC alloy, a strength−ductility combination that would normally require heterogeneous microstructures such as in dual-phase steels.
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