Research

9 pages, 4546 KiB

Open AccessCommunication

Improving Mechanical Properties of Fe-Mn-Co-Cr High-Entropy Alloy via Annealing after Cold Rolling

by Yukun Lv, Pingtao Song, Yuzhe Wang, Xuerou Zhao, Wei Gao, Jie Zhang, Yutian Lei and Jian Chen

Materials 2024, 17(3), 676; https://doi.org/10.3390/ma17030676 - 30 Jan 2024

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Abstract

The as-cast (Fe50Mn30Co10Cr10)97C2Mo1 HEA (high entropy alloy) was prepared and cold-rolled at 70%. Subsequently, annealing heat treatment at different temperatures (900 °C, 950 °C, 1000 °C) was carried out. The microstructure evolution and mechanical properties of the HEA were systematically investigated. The results [...] Read more.

The as-cast (Fe50Mn30Co10Cr10)97C2Mo1 HEA (high entropy alloy) was prepared and cold-rolled at 70%. Subsequently, annealing heat treatment at different temperatures (900 °C, 950 °C, 1000 °C) was carried out. The microstructure evolution and mechanical properties of the HEA were systematically investigated. The results showed that the HEA annealed at 900 °C and 950 °C exhibited uneven grain size and rich σ precipitation phase at grain boundaries. The grains began to grow and complete recrystallization, and no σ phases were observed in HEA annealed at 1000 °C, which resulted in a higher tensile strength of ~885 MPa and elongation of ~68% compared with other annealed HEAs. The higher volume fraction of annealing twins with 60°<111> orientation was produced in HEA annealed at 1000 °C, which enhanced the tensile strength and plasticity via the Twinning-induced plasticity (TWIP) mechanism. Full article

(This article belongs to the Special Issue Advances in High Entropy Alloys and High Entropy Carbides: Microstructural and Mechanical Properties and Modeling)

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11 pages, 6108 KiB

Open AccessCommunication

Improving Mechanical Properties of Co-Cr-Fe-Ni High Entropy Alloy via C and Mo Microalloying

by Yukun Lv, Yangyang Guo, Jie Zhang, Yutian Lei, Pingtao Song and Jian Chen

Materials 2024, 17(2), 529; https://doi.org/10.3390/ma17020529 - 22 Jan 2024

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Abstract

The as-cast [Co₄₀Cr₂₅(FeNi)_35−yMo_y]_100−xC_x (x = 0, 0.5, y = 3, 4, 5 at.%) HEAs (high-entropy alloys) were prepared by a vacuum arc melting furnace and were then hot rolled. The effect of [...] Read more.

The as-cast [Co₄₀Cr₂₅(FeNi)_35−yMo_y]_100−xC_x (x = 0, 0.5, y = 3, 4, 5 at.%) HEAs (high-entropy alloys) were prepared by a vacuum arc melting furnace and were then hot rolled. The effect of C and Mo elements on the microstructure evolution and mechanical properties of HEAs was systematically analyzed. The results showed that when no C atoms were added, the HEAs consisted of FCC + HCP dual-phase structure. In addition, as the Mo content increased, the grain size of the alloy increased from 17 μm to 47 μm. However, only the FCC phase appeared after adding 0.5 at.% carbon in Mo microalloyed HEAs, and the grain size of the Mo₄C_0.5 HEA decreased significantly. Due to the Mo atom content exceeding the solid solution limit, the carbides of Mo combined with the C element appeared in the Mo₅C_0.5 HEA. The strength of C and Mo microalloyed HEAs significantly increased compared to HEAs with no C added. However, the Mo₄C_0.5 HEA exhibited excellent comprehensive mechanical properties, which was superior to a majority of reported HEAs and conventional metal alloys. Its yield strength, tensile strength, and elongation were 757 MPa, 1186 MPa, and 69%, respectively. The strengthening mechanism was a combination of fine grain strengthening, TWIP effect, and solid solution strengthening. Full article

(This article belongs to the Special Issue Advances in High Entropy Alloys and High Entropy Carbides: Microstructural and Mechanical Properties and Modeling)

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10 pages, 6946 KiB

Open AccessArticle

The Microstructures, Mechanical Properties, and Deformation Mechanism of B2-Hardened NbTiAlZr-Based Refractory High-Entropy Alloys

by Guangquan Tang, Xu Shao, Jingyu Pang, Yu Ji, Aimin Wang, Jinguo Li, Haifeng Zhang and Hongwei Zhang

Materials 2023, 16(24), 7592; https://doi.org/10.3390/ma16247592 - 11 Dec 2023

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Abstract

The NbTiAlZrHfTaMoW refractory high-entropy alloy (RHEA) system with the structure of the B2 matrix (antiphase domains) and antiphase domain boundaries was firstly developed. We conducted the mechanical properties of the RHEAs at 298 K, 1023 K, 1123 K, and 1223 K, as well [...] Read more.

The NbTiAlZrHfTaMoW refractory high-entropy alloy (RHEA) system with the structure of the B2 matrix (antiphase domains) and antiphase domain boundaries was firstly developed. We conducted the mechanical properties of the RHEAs at 298 K, 1023 K, 1123 K, and 1223 K, as well as typical deformation characteristics. The RHEAs with low density (7.41~7.51 g/cm³) have excellent compressive-specific yield strength (

σ_{YS}

/

ρ

) at 1023 K (~131 MPa·cm³/g) and 1123 K (~104.2 MPa·cm³/g), respectively, which are far superior to most typical RHEAs. And, they still keep appropriate plastic deformability at room temperature (ε > 0.35). The superior specific yield strengths are mainly attributed to the solid solution strengthening induced by the Zr element. The formation of the dislocation slip bands with [111](10

\overline{1}

) and [111](11

\overline{2}

) directions and their interaction provide considerable plastic deformation capability. Meanwhile, dynamic recrystallization and dislocation annihilation accelerate the continuous softening after yielding at 1123 K. Full article

(This article belongs to the Special Issue Advances in High Entropy Alloys and High Entropy Carbides: Microstructural and Mechanical Properties and Modeling)

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12 pages, 6970 KiB

Open AccessArticle

The Effects of the Al and Zr Contents on the Microstructure Evolution of Light-Weight Al_xNbTiVZr_y High Entropy Alloy

by Hongwei Yan, Rui Liu, Shenglong Li, Yong’an Zhang, Wei Xiao, Boyu Xue, Baiqing Xiong, Xiwu Li and Zhihui Li

Materials 2023, 16(24), 7581; https://doi.org/10.3390/ma16247581 - 09 Dec 2023

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Abstract

To investigate the comprehensive effects of the Al and Zr element contents on the microstructure evolution of the AlNbTiVZr series light-weight refractory high entropy alloys (HEAs), five samples were studied. Samples with different compositions were designated Al_1.5NbTiVZr, Al_1.5NbTiVZr_0.5 [...] Read more.

To investigate the comprehensive effects of the Al and Zr element contents on the microstructure evolution of the AlNbTiVZr series light-weight refractory high entropy alloys (HEAs), five samples were studied. Samples with different compositions were designated Al_1.5NbTiVZr, Al_1.5NbTiVZr_0.5, AlNbTiVZr, AlNbTiVZr_0.5, and Al_0.5NbTiVZr_0.5. The results demonstrated that the actual density of the studied HEA samples ranged from 5.291 to 5.826 g·cm⁻³. The microstructure of these HEAs contains a solid solution phase with a BCC structure and a Laves phase. The Laves phase was further identified as the ZrAlV intermetallic compound by TEM observations. The microstructure of the AlNbTiVZr series HEAs was affected by both the Al and Zr element contents, whereas the Zr element showed a more dominant effect due to Zr atoms occupying the core position of the ZrAlV Laves phase (C14 structure). Therefore, the as-cast Al_0.5NbTiVZr_0.5 sample exhibits the best room temperature compression property with a compression strength (σ_p) of 1783 MPa and an engineering strain of 28.8% due to having the lowest ZrAlV intermetallic compound area fraction (0.7%), as characterized by the EBSD technique. Full article

(This article belongs to the Special Issue Advances in High Entropy Alloys and High Entropy Carbides: Microstructural and Mechanical Properties and Modeling)

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18 pages, 22154 KiB

Open AccessArticle

Effects of Cold Rolling or Precipitation Hardening Treatment on the Microstructure, Mechanical Properties, and Corrosion Resistance of Ti-Rich Metastable Medium-Entropy Alloys

by Hsueh-Chuan Hsu, Ka-Kin Wong, Shih-Ching Wu, Chun-Yu Huang and Wen-Fu Ho

Materials 2023, 16(24), 7561; https://doi.org/10.3390/ma16247561 - 08 Dec 2023

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Abstract

Titanium-rich metastable medium-entropy alloys, designed for low elastic moduli, sacrifice strength. However, enhancing their mechanical strength is crucial for bio-implant applications. This study aims to enhance the mechanical properties and corrosion resistance of a metastable Ti₈₀–Nb₁₀–Mo₅–Sn₅ [...] Read more.

Titanium-rich metastable medium-entropy alloys, designed for low elastic moduli, sacrifice strength. However, enhancing their mechanical strength is crucial for bio-implant applications. This study aims to enhance the mechanical properties and corrosion resistance of a metastable Ti₈₀–Nb₁₀–Mo₅–Sn₅ medium-entropy alloy using various treatments, including cold rolling (at 50% and 75% reduction) and precipitation hardening (at room temperature, 150 °C, 350 °C, 550 °C, and 750 °C). The results showed that the alloy underwent a stress-induced martensitic transformation during the rolling process. Notably, the α phase was precipitated in the β grain boundaries after 30 days of precipitation hardening at room temperature. The yield strengths of the alloy increased by 51% and 281.9% after room-temperature precipitation and 75% cold rolling, respectively. In potentiodynamic corrosion tests conducted in phosphate-buffered saline solution, the pitting potentials of the alloy treated using various conditions were higher than 1.8 V, and no pitting holes were observed on the surface of the alloys. The surface oxide layer of the alloy was primarily composed of TiO₂, Nb₂O₅, MoO₃, and SnO₂, contributing to the alloy’s exceptional corrosion and pitting resistance. The 75% rolled Ti₈₀–Nb₁₀–Mo₅–Sn₅ demonstrates exceptional mechanical properties and high corrosion resistance, positioning it as a promising bio-implant candidate. Full article

(This article belongs to the Special Issue Advances in High Entropy Alloys and High Entropy Carbides: Microstructural and Mechanical Properties and Modeling)

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11 pages, 5629 KiB

Open AccessArticle

Microstructure, Mechanical and Tribological Properties of High-Entropy Carbide (MoNbTaTiV)C₅

by Shubo Zhang, Falian Qin, Maoyuan Gong, Zihao Wu, Meiling Liu, Yuhong Chen and Wanxiu Hai

Materials 2023, 16(11), 4115; https://doi.org/10.3390/ma16114115 - 31 May 2023

Cited by 2 | Viewed by 932

Abstract

High-entropy carbide (NbTaTiV)C₄ (HEC4), (MoNbTaTiV)C₅ (HEC5), and (MoNbTaTiV)C₅-SiC (HEC5S) multiphase ceramics were prepared by spark plasma sintering (SPS) at 1900 to 2100 °C, using metal carbide and silicon carbide (SiC) as raw materials. Their microstructure, and mechanical and tribological [...] Read more.

High-entropy carbide (NbTaTiV)C₄ (HEC4), (MoNbTaTiV)C₅ (HEC5), and (MoNbTaTiV)C₅-SiC (HEC5S) multiphase ceramics were prepared by spark plasma sintering (SPS) at 1900 to 2100 °C, using metal carbide and silicon carbide (SiC) as raw materials. Their microstructure, and mechanical and tribological properties were investigated. The results showed that the (MoNbTaTiV)C₅ synthesized at 1900–2100 °C had a face-centered cubic structure and density higher than 95.6%. The increase in sintering temperature was conducive to the promotion of densification, growth of grains, and diffusion of metal elements. The introduction of SiC helped to promote densification but weakened the strength of the grain boundaries. The average specific wear rates for HEC4 were within an order of magnitude of 10⁻⁵ mm³/N·m, and for HEC5 and HEC5S were within a range of 10⁻⁷ to 10⁻⁶ mm³/N·m. The wear mechanism of HEC4 was abrasion, while that of HEC5 and HEC5S was mainly oxidation wear. Full article

(This article belongs to the Special Issue Advances in High Entropy Alloys and High Entropy Carbides: Microstructural and Mechanical Properties and Modeling)

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10 pages, 11498 KiB

Open AccessArticle

Microstructure and Properties of Ti(C,N)-Based Cermets with Al_xCoCrFeNiTi Binder

by Meiling Liu, Zhen Sun, Peng Liu, Wanxiu Hai and Yuhong Chen

Materials 2023, 16(7), 2894; https://doi.org/10.3390/ma16072894 - 05 Apr 2023

Cited by 2 | Viewed by 879

Abstract

Al_xCoCrFeNiTi (x = 0.1, 0.3, 0.6, 1) powders were prepared via mechanical alloying and were used as binders for SPS-produced Ti(C,N)-based cermets. The effects of AlxCoCrFeNiTi binder on phase composition, morphology, room-temperature mechanical properties, and oxidation resistance of cermets were studied. [...] Read more.

Al_xCoCrFeNiTi (x = 0.1, 0.3, 0.6, 1) powders were prepared via mechanical alloying and were used as binders for SPS-produced Ti(C,N)-based cermets. The effects of AlxCoCrFeNiTi binder on phase composition, morphology, room-temperature mechanical properties, and oxidation resistance of cermets were studied. The research showed that cermets with Al_xCoCrFeNiTi binders exhibited a more homogeneous core–rim structure than cermets with cobalt binders. The Vickers hardness and fracture toughness of cermets with Al_xCoCrFeNiTi binders increased with the aluminum molar ratio due to the grain refinement and solid solution strengthening effect of carbonitrides. After static oxidation at 1000 °C, the mass gain of the cermets with Al_xCoCrFeNiTi binders changed according to a quasi-parabolic law, and the lowest mass gain was obtained in the cermet with Al_0.6CoCrFeNiTi binder. The oxidation kinetics curve of the benchmark cermet with cobalt followed a linear law. The oxidation product of Ti(C,N)-based cermet with cobalt was rich in TiO₂, and the Ti(C,N)-based cermets with Al_xCoCrFeNiTi binders were transformed into complex oxides, such as NiMoO₄, NiWO₄, FeMoO₄, Fe₃Ti₃O₉, and Ni₃TiO₇. The oxide layer on the cermet with Al_0.6CoCrFeNiTi appeared to be dense and protective, which inhibited the diffusion of oxygen into the cermet and improved the oxidation resistance of the final product. Full article

(This article belongs to the Special Issue Advances in High Entropy Alloys and High Entropy Carbides: Microstructural and Mechanical Properties and Modeling)

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9 pages, 50022 KiB

Open AccessArticle

Effect of Si on Microstructure and Mechanical Properties of FeCrNi Medium Entropy Alloys

by Fang Ding, Yuankui Cao, Ao Fu, Jian Wang, Weidong Zhang, Jingwen Qiu and Bin Liu

Materials 2023, 16(7), 2697; https://doi.org/10.3390/ma16072697 - 28 Mar 2023

Cited by 1 | Viewed by 1276

Abstract

FeCrNi medium entropy alloy (MEA) has been widely regarded for its excellent mechanical properties and corrosion resistance. However, insufficient strength limits its industrial application. Intermetallic particle dispersion strengthening is considered to be an effective method to improve strength, which is expected to solve [...] Read more.

FeCrNi medium entropy alloy (MEA) has been widely regarded for its excellent mechanical properties and corrosion resistance. However, insufficient strength limits its industrial application. Intermetallic particle dispersion strengthening is considered to be an effective method to improve strength, which is expected to solve this problem. In this work, microstructural evolution and mechanical behavior of FeCrNi MEA with different Si content were investigated. We found that the precipitation of fine σ particles can be formed in situ by thermomechanical treatment of Si doping FeCrNi MEAs. The FeCrNiSi_0.15 MEA exhibits a good combination of strength and ductility, with yield strength and tensile elongation of 1050 MPa and 7.84%, respectively. The yield strength is almost five times that of the as-cast FeCrNi MEA. The strength enhancement is mainly attributed to the grain-boundary strengthening and precipitation strengthening caused by fine σ particles. Full article

(This article belongs to the Special Issue Advances in High Entropy Alloys and High Entropy Carbides: Microstructural and Mechanical Properties and Modeling)

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16 pages, 27431 KiB

Open AccessArticle

High-Strength Ductility Joining of Multicomponent Alloy to 304 Stainless Steel Using Laser Welding Technique

by Junjie Wang, Fei Peng, Li Zhou, Yajun Luo, Weidong Zhang and Zhenggang Wu

Materials 2023, 16(6), 2374; https://doi.org/10.3390/ma16062374 - 16 Mar 2023

Cited by 3 | Viewed by 1217

Abstract

In this work, a series of multicomponent alloys (CoCrFeNi, CoCrNi, and CoNiV) were laser welded with 304 stainless steel (304ss), and detailed comparisons on microstructural characteristics and mechanical properties were conducted for dissimilar laser welded joints. It is revealed that all of the [...] Read more.

In this work, a series of multicomponent alloys (CoCrFeNi, CoCrNi, and CoNiV) were laser welded with 304 stainless steel (304ss), and detailed comparisons on microstructural characteristics and mechanical properties were conducted for dissimilar laser welded joints. It is revealed that all of the dissimilar laser welded samples possessed defect-free joints and the corresponding fusion zone consisting of fcc single-phase showed homogeneous element distribution accompanied by a narrow element gradient in the vicinity of the fusion zone boundary. After laser welding with identical welding parameters, equiaxed grain was observed on the side of multicomponent alloy, while coarse columnar grain was obtained on the side of 304ss. Especially, the columnar grains of the fusion zone on the side of 304ss disclosed preferential <001> growth direction in the CoCrFeNi/304ss and CoCrNi/304ss welded joints. Furthermore, all of the dissimilar laser welded joints were fractured in the fusion zone, attributing to the drastic loss of strength in the fusion zone with coarsened grain. It is worth noting that a special lamellar structure that merged by dimples was found in the fracture surface of the CoNiV/304ss joint, closely related to the existence of the V-enriched region. Finally, a high strength–ductile synergy can be achieved by laser welding CoNiV alloy to 304ss, which showed a yield strength of 338 MPa, ultimate tensile strength of 686 MPa, and total elongation of 28.9%. These excellent mechanical properties prevailed in the potential of a CoNiV/304ss laser welded joint to be applied as a structural material. Full article

(This article belongs to the Special Issue Advances in High Entropy Alloys and High Entropy Carbides: Microstructural and Mechanical Properties and Modeling)

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11 pages, 5262 KiB

Open AccessArticle

Preparation and Microstructure of High-Activity Spherical TaNbTiZr Refractory High-Entropy Alloy Powders

by Shenghan Gao, Ao Fu, Zhonghao Xie, Tao Liao, Yuankui Cao and Bin Liu

Materials 2023, 16(2), 791; https://doi.org/10.3390/ma16020791 - 13 Jan 2023

Cited by 1 | Viewed by 1222

Abstract

High-activity spherical TaNbTiZr refractory high-entropy alloy (REHA) powders were successfully prepared by electrode induction melting gas atomization (EIGA) and plasma rotating electrode process (PREP) methods. Both the EIGAed and PREPed TaNbTiZr RHEA powders have a single-phase body-centered cubic (BCC) structure and low oxygen [...] Read more.

High-activity spherical TaNbTiZr refractory high-entropy alloy (REHA) powders were successfully prepared by electrode induction melting gas atomization (EIGA) and plasma rotating electrode process (PREP) methods. Both the EIGAed and PREPed TaNbTiZr RHEA powders have a single-phase body-centered cubic (BCC) structure and low oxygen content. Compared with the EIGAed powders, the PREPed powders exhibit higher sphericity and smoother surface, but larger particle size. The average particle sizes of the EIGAed and PREPed powders are 51.8 and 65.9 μm, respectively. In addition, both the coarse EIGAed and PREPed powders have dendritic structure, and the dendrite size of the EIGAed powders is larger than that of the PREPed powders. Theoretical calculation indicates that the cooling rate of the PREPed powders is one order of magnitude higher than that of the EIGAed powders during the solidification process, and the dendritic structure has more time to grow during EIGA, which is the main reason for the coarser dendrite size of the EIGAed powders. Full article

(This article belongs to the Special Issue Advances in High Entropy Alloys and High Entropy Carbides: Microstructural and Mechanical Properties and Modeling)

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