scholarly journals EFFECT OF γ′-PHASE PARTICLES ON THE MECHANICAL BEHAVIOR AND DEFORMATION MECHANISM OF (CoCrFeNi)94Ti2Al4 HIGH ENTROPY ALLOY SINGLE CRYSTALS

2021 ◽  
pp. 84-90
Author(s):  
A. A. Saraeva ◽  
Keyword(s):  
Mechanical Behavior ◽  
Strain Hardening ◽  
Single Crystals ◽  
Yield Point ◽  
Volume Fraction ◽  
High Entropy Alloy ◽  
Strong Temperature Dependence ◽  
Face Centered Cubic ◽  
High Entropy ◽  
Hardening Coefficient

Recently, the interest of researchers has focused on a new FCC class (FCC – face-centered cubic lattice) high-entropy alloys (HEA), due to their unique properties – high values of the strain hardening coefficient, good plasticity, and ductile fracture at low test temperatures. Such a combination of properties in an FCC of HEA is achieved by mixing five or more elements in equal atomic proportions. Due to the strong temperature dependence of stresses at the σ0.1(T) yield point, these alloys have low σ0.1 values at temperatures above room temperature, which hinders their practical application. A precipitation hardening is an effective way to achieve high strength and is successfully used for hardening HEA FCC. The paper studied the influence of ageing at 923 K for 4 hours and at 1073 K for 18 and 30 hours on the mechanical behavior of single crystals of (CoCrFeNi)94Ti2Al4 (at.%) HEA FCC oriented along the [001] direction under tension. Ageing at 923 K for 4 hours and at 1073 K for 18 and 30 hours leads to the precipitation of γ′-phase particles, the size and volume fraction of which depend on the ageing temperature and time. The γ′-phase particles precipitation leads to an increase in stresses at the yield point from 47 MPa (ageing at 923 K, 4 hours) to 226 MPa (ageing at 1073 K, 30 hours) relative to quenched crystals at 296 K. The study identified the dependence of the strain hardening coefficient, plasticity, and the maximum stress level before fracture on heat treatment. The author discussed the reasons for the growth of stresses at the yield point and the strain hardening coefficient upon precipitation of γ′-phase particles.

scholarly journals High-Strength Behavior of the Al0.3CoCrFeNi High-Entropy Alloy Single Crystals

Metals ◽  
2020 ◽  
Vol 10 (9) ◽  
pp. 1149
Author(s):  
Irina V. Kireeva ◽  
Yuriy I. Chumlyakov ◽  
Zinaida V. Pobedennaya ◽  
Anna V. Vyrodova ◽  
Anastasia A. Saraeva
Keyword(s):  
Single Crystals ◽  
Yield Point ◽  
Stress Level ◽  
High Stress ◽  
High Strength ◽  
Orientation Dependence ◽  
Temperature Deformation ◽  
High Entropy Alloy ◽  
Shear Stresses ◽  
High Entropy

The main disadvantage of fcc (face-centred cubic lattice) high-entropy alloys is the low stress level at the yield point (σ0.1) at a test temperature above room temperature. This restricts their practical application at high test temperatures from 773 K to 973 K. In this study, we found that a high stress level was reached at the yield point σ0.1 ≈ G/100–G/160 (G is the shear modulus) of the [001]- and [1¯44]-oriented crystals of the Co23.36Cr23.29Fe23.80Ni21.88Al7.67 (Al0.3CoCrFeNi) high-entropy alloy (HEA) within a wide temperature range of 77–973 K under tension, due to the occurrence, of nanotwins, multipoles, dislocations under plastic deformation at 77 K and the subsequent precipitation of ordered L12 and B2 particles. It was shown that grain boundaries are not formed and the samples remain in a single-crystal state after low-temperature deformation and subsequent ageing at 893 K for 50 h. Achieving a high-strength state in the Al0.3CoCrFeNi HEA single crystals induces the orientation dependence of the critical resolved shear stresses (τcr) at T ≥ 200 K (τcr[1¯44] > τcr[001]), which is absent in the initial single-phase crystals, weakens the temperature dependence of σ0.1 above 573 K, and reduces plasticity to 5–13% in the [1¯44] orientation and 15–20% in the [001] orientation.

scholarly journals Formation and Anisotropic Mechanical Behavior of Stacking Fault Tetrahedron in Ni and CoCrFeNiMn High-Entropy Alloy

2022 ◽  
Vol 8 ◽  
Author(s):  
Sen Hu ◽  
Tao Fu ◽  
Qihao Liang ◽  
Shayuan Weng ◽  
Xiang Chen ◽  
...  
Keyword(s):  
Mechanical Behavior ◽  
Critical Stress ◽  
Three Dimensional ◽  
Stacking Faults ◽  
Stacking Fault ◽  
High Entropy Alloy ◽  
Face Centered Cubic ◽  
High Entropy ◽  
Stacking Fault Tetrahedron ◽  
Dynamics Simulations

Stacking fault tetrahedron (SFT) is a kind of detrimental three-dimensional defect in conventional face-centered cubic (FCC) structural metals; however, its formation and anisotropic mechanical behavior in a CoCrFeNiMn high-entropy alloy (HEA) remain unclear. In this work, we first performed molecular dynamics simulations to verify the applicability of the Silcox-Hirsch mechanism in the CoCrFeNiMn HEA. The mechanical responses of the SFT to shear stress in different directions and that of the pure Ni counterpart were simulated, and the evolutions of the atomic structures of the SFTs during shear were analyzed in detail. Our results revealed that the evolution of the SFT has different patterns, including the annihilation of stacking faults, the formation and expansion of new stacking faults, and insignificant changes in stacking faults. It was found that the effects of SFT on the elastic properties of Ni and HEA are negligible. However, the introduction of SFT would reduce the critical stress, while the critical stress of the CoCrFeNiMn HEA is much less sensitive to SFT than that of Ni.

Friction Stir Welding of the Carbon-Doped Dual-Phase High Entropy Alloy

2021 ◽  
Vol 316 ◽  
pp. 364-368
Author(s):  
Dmitry Shaysultanov ◽  
Kazimzhon Raimov ◽  
Nikita Stepanov
Keyword(s):  
Friction Stir Welding ◽  
Volume Fraction ◽  
Cast Alloy ◽  
High Yield ◽  
High Entropy Alloy ◽  
Induction Melting ◽  
Face Centered Cubic ◽  
High Entropy ◽  
Friction Stir ◽  
Average Grain Size

Fe49Mn30Cr10Co10C1 high entropy alloy (HEA) is produced by induction melting. The as-cast alloy is cold rolled and annealed at 900°C, to produce fine recrystallized structure before friction stir welding (FSW). The structure of the annealed alloy consists of a recrystallized face-centered cubic (fcc, γ) and hexagonal close-packed (hcp, ε) phases with volume fractions of 91% and 5%, respectively, as well as M23C6 carbides with the volume fraction of 4%. Sound weld without visible defects, such as porosity or cracks, are obtained. Friction stir welding results in a decrease in the average grain size from 7.0 to 1.9 μm in the stir zone. The volume fraction of the M23C6 carbides decreases to 1% after FSW. The alloy shows high yield strength and ultimate tensile strength of 475 MPa and 865 MPa, respectively, together with elongation of 70%.

scholarly journals In Situ Development and High Temperature Features of CoCrFeNi-M6Cp High Entropy-Alloy Based Hardmetal

Metals ◽  
2020 ◽  
Vol 10 (3) ◽  
pp. 408
Author(s):  
Huizhong Li ◽  
He Lin ◽  
Xiaopeng Liang ◽  
Weiwei He ◽  
Bin Liu ◽  
...  
Keyword(s):  
Tensile Strength ◽  
Ultimate Tensile Strength ◽  
Yield Strength ◽  
Volume Fraction ◽  
High Entropy Alloy ◽  
Face Centered Cubic ◽  
High Entropy ◽  
Average Grain Size ◽  
Carbide Particles

In this work, an in-situ CoCrFeNi-M6Cp high entropy-alloy (HEA) based hardmetal with a composition of Co25Cr21Fe18Ni23Mo7Nb3WC2 was fabricated by the powder metallurgy (PM) method. Microstructures and mechanical properties of this HEA were characterized and analyzed. The results exhibit that this HEA possesses a two-phase microstructure consisting of the face-centered cubic (FCC) matrix phase and the carbide M6C phase. This HEA has an average grain size of 2.2 μm, and the mean size and volume fraction of carbide particles are 1.2 μm and 20%. The tensile tests show that the alloy has a yield strength of 573 MPa, ultimate tensile strength of 895 MPa and elongation of 5.5% at room temperature. The contributions from different strengthening mechanisms in this HEA were calculated. The grain boundary strengthening is the dominant strengthening mechanism, and the carbide particles are significant for the further enhancement of yield strength by the dislocation strengthening and Orowan strengthening. In addition, with increasing temperatures from 600 °C to 900 °C, the HEA shows a reduced yield strength (YS) from 473 MPa to 142 MPa, a decreased ultimate tensile strength (UTS) from 741 MPa to 165 MPa and an enhanced elongation from 10.5% to 31%.

scholarly journals Welding of High Entropy Alloys—A Review

Entropy ◽  
2019 ◽  
Vol 21 (4) ◽  
pp. 431 ◽  
Author(s):  
Jing Guo ◽  
Cong Tang ◽  
Glynn Rothwell ◽  
Lisa Li ◽  
Yun-Che Wang ◽  
...  
Keyword(s):  
Welded Joints ◽  
Volume Fraction ◽  
Future Application ◽  
Limiting Factor ◽  
High Entropy Alloy ◽  
Face Centered Cubic ◽  
High Entropy ◽  
Friction Stir ◽  
Welded Structure ◽  
Welding Processes

High-entropy alloy (HEA) offers great flexibility in materials design with 3–5 principal elements and a range of unique advantages such as good microstructure stability, mechanical strength over a broad range of temperatures and corrosion resistance, etc. Welding of high entropy alloy, as a key joining method, is an important emerging area with significant potential impact to future application-oriented research and technological developments in HEAs. The selection of feasible welding processes with optimized parameters is essential to enhance the applications of HEAs. However, the structure of the welded joints varies with material systems, welding methods and parameters. A systemic understanding of the structures and properties of the weldment is directly relevant to the application of HEAs as well as managing the effect of welding on situations such as corrosion that are known to be a service life limiting factor of welded structures in conditions such as marine environments. In this paper, key recent work on welding of HEAs is reviewed in detail focusing on the research of main HEA systems when applying different welding techniques. The experimental details including sample preparation, sample size (thickness) and welding conditions reflecting energy input are summarized and key issues are highlighted. The microstructures and properties of different welding zones, in particular the fusion zone (FZ) and the heat affected zones (HAZ), formed with different welding methods are compared and presented in details and the structure-property relationships are discussed. The work shows that the weldability of HEAs varies with the HEA composition groups and the welding method employed. Arc and laser welding of AlCoCrFeNi HEAs results in lower hardness in the FZ and HAZ and reduced overall strength. Friction stir welding results in higher hardness in the FZ and achieves comparable/higher strength of the welded joints in tensile tests. The welded HEAs are capable of maintaining a reasonable proportion of the ductility. The key structure changes including element distribution, the volume fraction of face centered cubic (FCC) and body centered cubic (BCC) phase as well as reported changes in the lattice constants are summarized and analyzed. Detailed mechanisms governing the mechanical properties including the grain size-property/hardness relationship in the form of Hall–Petch (H–P) effect for both bulk and welded structure of HEAs are compared. Finally, future challenges and main areas to research are highlighted.

scholarly journals Magnetic, electrical and mechanical properties of Fe40Mn40Co10Cr10 high entropy alloy

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
M. Egilmez ◽  
W. Abuzaid
Keyword(s):  
Temperature Dependence ◽  
Volume Fraction ◽  
Electron Backscatter Diffraction ◽  
Magnetic Moments ◽  
High Entropy Alloy ◽  
Zero Field ◽  
Face Centered Cubic ◽  
High Entropy ◽  
Phase Volume Fraction ◽  
Crystallographic Slip

AbstractA prototypical, single-phase, and non-equiatomic high entropy alloy Fe40Mn40Co10Cr10 has been mechanically deformed at room and cryogenic temperatures. Plastic deformation was accommodated via crystallographic slip at room temperature while transformation induced plasticity (TRIP) has been observed in samples deformed at 77 K. The stress-induced martensitic transformation occurred from face-centered cubic (FCC) to hexagonal close-packed (HCP) structures. A detailed electron backscatter diffraction analysis was utilized to detect phase change and evaluate the evolution of the HCP phase volume fraction as a function of plastic strain. Physical properties of undeformed and deformed samples were measured to elucidate the effect of deformation-induced phase transitions on the magnetic and electrical properties of Fe40Mn40Co10Cr10 alloy. Relatively small magnetic moments along with non-saturating magnetic field dependencies suggest that the ground state in the considered material is ferrimagnetic ordering with coexisting antiferromagnetic phase. The temperature evolution of the coercive fields has been revealed for all samples. The magnitudes of the coercive fields place the considered system into the semi-hard magnetic alloys category. The temperature dependence of the zero-field cooled (ZFC) and field cooled (FC) magnetization was measured for all samples in the low field regime and the origin of irreversibility in ZFC/FC curves was discussed. Besides, the temperature dependence of the resistivity in all samples was measured and the possible conduction mechanisms were discussed.

Microstructure Refinement in the CoCrFeNiMn High Entropy Alloy under Plastic Straining

2016 ◽  
Vol 879 ◽  
pp. 1853-1858 ◽  
Author(s):  
Nikita Stepanov ◽  
Dmitry Shaysultanov ◽  
Nikita Yurchenko ◽  
Margarita Klimova ◽  
Sergey Zherebtsov ◽  
...  
Keyword(s):  
Yield Strength ◽  
Volume Fraction ◽  
Dominant Role ◽  
Mechanical Twinning ◽  
Cubic Phase ◽  
High Entropy Alloy ◽  
Face Centered Cubic ◽  
Cryogenic Temperatures ◽  
High Entropy ◽  
Average Grain Size

The effect of plastic deformation under various conditions of the equiatomic CoCrFeNiMn alloy with single face-centered cubic phase structure was studied. The alloy was rolled at room and cryogenic temperatures, and uniaxially compressed at room temperature and temperatures of 600-1100°C with different height reductions. In addition, multiaxial forging at 900-1000°C was performed. Scanning and transmission electron microscopy, including EBSD analysis, was widely employed to characterize microstructure of the deformed alloy. At room and cryogenic temperatures, mechanical twinning and shear banding plays play dominant role in microstructure evolution. Extensive refinement of the microstructure occurs as the result of rolling with reduction of 80%. During deformation at 600-1100°C, discontinuous dynamic recrystallization takes place. The recrystallized grains size and their volume fraction increases with increase of deformation temperature. Multiaxial forging at 900-1000°C was used to produce fully recrystallized structure with average grain size of 6.7 μm. The alloy in the initial condition had low yield strength of 160 Mpa but remarkable tensile ductility of 68%. Rolling substantial increases yield strength to 1120-1290 MPa, but results in loss of ductility. After multiaxial forging the alloy has balanced combination of properties – yield strength of 280 MPa and elongation of 56%.

Effect of Aging Temperature on Microstructure and Hardness of CoCrFeNiTi0.5 High Entropy Alloy

2014 ◽  
Vol 789 ◽  
pp. 48-53 ◽  
Author(s):  
Yong Dong ◽  
Qiu Shi Chen ◽  
Yi Ping Lu ◽  
Peng Chao Zhang ◽  
Ting Ju Li
Keyword(s):  
Aging Temperature ◽  
Volume Fraction ◽  
High Entropy Alloy ◽  
Induction Melting ◽  
Face Centered Cubic ◽  
Micro Hardness ◽  
Rich Phase ◽  
Σ Phase ◽  
High Entropy ◽  
Temperature Range

A bulk casting ingot (Ø70 × 150mm) of CoCrFeNiTi0.5 high entropy alloy was prepared by vacuum medium frequency induction melting. The samples from the ingot were aged for 12h in the temperature range of 900-1100°C and then quenched in water to investigate the effect of aging temperature on the microstructure and hardness of CoCrFeNiTi0.5 alloy. The crystalline structure of as-cast CoCrFeNiTi0.5 alloy consisted of the principal face-centered cubic (FCC) dendrite phase plus (Ni, Ti)-rich R phase, (Fe, Cr)-rich σ phase, (Co, Ti)-rich Laves phase within the inter-dendrite area. The dendrite contained approximately equivalent amount of Co, Cr, Fe, Ni and a smaller amount of Ti element. After aging treatment in the temperature range of 900-1000°C, the (Co, Ti)-rich phase disappeared while the amount of (Ni, Ti)-rich phase and (Fe, Cr)-rich phase increased. But the volume fraction of FCC dendrite phase increased and the intermetallic phases decreased after aging at 1100°C. The micro-hardness and the macro-hardness of the as-cast CoCrFeNiTi0.5 alloy were HV616.8 and HRC52, respectively. After heat treatment at 1000°C, the micro-hardness and macro-hardness decreased from HV616.8 to HV386.8 and from HRC52 to HRC42.7, respectively.

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