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.

scholarly journals Generalized Stacking Fault Energy of Al-Doped CrMnFeCoNi High-Entropy Alloy

Nanomaterials ◽  
2019 ◽  
Vol 10 (1) ◽  
pp. 59 ◽  
Author(s):  
Xun Sun ◽  
Hualei Zhang ◽  
Wei Li ◽  
Xiangdong Ding ◽  
Yunzhi Wang ◽  
...  
Keyword(s):  
Interfacial Energy ◽  
Stacking Fault ◽  
Stacking Fault Energy ◽  
High Entropy Alloy ◽  
High Entropy Alloys ◽  
Face Centered Cubic ◽  
High Entropy ◽  
Al Content ◽  
Generalized Stacking Fault ◽  
Generalized Stacking Fault Energy

Using first-principles methods, we investigate the effect of Al on the generalized stacking fault energy of face-centered cubic (fcc) CrMnFeCoNi high-entropy alloy as a function of temperature. Upon Al addition or temperature increase, the intrinsic and extrinsic stacking fault energies increase, whereas the unstable stacking fault and unstable twinning fault energies decrease monotonously. The thermodynamic expression for the intrinsic stacking fault energy in combination with the theoretical Gibbs energy difference between the hexagonal close packed (hcp) and fcc lattices allows one to determine the so-called hcp-fcc interfacial energy. The results show that the interfacial energy is small and only weakly dependent on temperature and Al content. Two parameters are adopted to measure the nano-twinning ability of the present high-entropy alloys (HEAs). Both measures indicate that the twinability decreases with increasing temperature or Al content. The present study provides systematic theoretical plasticity parameters for modeling and designing high entropy alloys with specific mechanical properties.

Ultrastrong Al0.1CoCrFeNi high-entropy alloys at small scales: effects of stacking faults vs. nanotwins

Nanoscale ◽  
2018 ◽  
Vol 10 (28) ◽  
pp. 13329-13334 ◽  
Author(s):  
Xiaobin Feng ◽  
Jinyu Zhang ◽  
Kai Wu ◽  
Xiaoqing Liang ◽  
Gang Liu ◽  
...  
Keyword(s):  
Stacking Faults ◽  
Maximum Strength ◽  
High Entropy Alloy ◽  
High Entropy Alloys ◽  
Face Centered Cubic ◽  
High Entropy ◽  
Small Scales ◽  
Face Centered

The present stacking faulted and nanotwinned Al0.1CoCrFeNi high-entropy alloy pillars achieved the maximum strength among face-centered cubic structured metals.

Molecular dynamics simulation of screw dislocation interaction with stacking fault tetrahedron in face-centered cubic Cu

2007 ◽  
Vol 22 (10) ◽  
pp. 2758-2769 ◽  
Author(s):  
Hyon-Jee Lee ◽  
Jae-Hyeok Shim ◽  
Brian D. Wirth
Keyword(s):  
Molecular Dynamics ◽  
Screw Dislocation ◽  
Stacking Fault ◽  
Dynamics Simulation ◽  
Face Centered Cubic ◽  
Dislocation Interaction ◽  
Complete Absorption ◽  
Stacking Fault Tetrahedron ◽  
Face Centered ◽  
Dynamics Simulations

The interaction of a gliding screw dislocation with stacking fault tetrahedron (SFT) in face-centered cubic (fcc) copper (Cu) was studied using molecular dynamics simulations. Upon intersection, the screw dislocation spontaneously cross slips on the SFT face. One of the cross-slipped Shockley partials glides toward the SFT base, partially absorbing the SFT. At low applied stress, partial absorption produces a superjog, with detachment of the trailing Shockley partial via an Orowan process. This leaves a small perfect SFT and a truncated base behind, which subsequently form a sheared SFT with a pair of opposite sense ledges. At higher applied shear stress, the ledges can self-heal by gliding toward an SFT apex and transform the sheared SFT into a perfect SFT. However, complete absorption or collapse of an SFT (or sheared SFT) by a moving screw dislocation is not observed. These observations provide insights into defect-free channel formation in deformed irradiated Cu.

scholarly journals Tunable stacking fault energies by tailoring local chemical order in CrCoNi medium-entropy alloys

2018 ◽  
Vol 115 (36) ◽  
pp. 8919-8924 ◽  
Author(s):  
Jun Ding ◽  
Qin Yu ◽  
Mark Asta ◽  
Robert O. Ritchie
Keyword(s):  
Mechanical Behavior ◽  
Energy Difference ◽  
Stacking Fault ◽  
Face Centered Cubic ◽  
Structure Property ◽  
Chemical Order ◽  
High Entropy ◽  
Structure Property Relationships ◽  
The Face ◽  
Robust Processing

High-entropy alloys (HEAs) are an intriguing new class of metallic materials due to their unique mechanical behavior. Achieving a detailed understanding of structure–property relationships in these materials has been challenged by the compositional disorder that underlies their unique mechanical behavior. Accordingly, in this work, we employ first-principles calculations to investigate the nature of local chemical order and establish its relationship to the intrinsic and extrinsic stacking fault energy (SFE) in CrCoNi medium-entropy solid-solution alloys, whose combination of strength, ductility, and toughness properties approaches the best on record. We find that the average intrinsic and extrinsic SFE are both highly tunable, with values ranging from −43 to 30 mJ⋅m−2 and from −28 to 66 mJ⋅m−2, respectively, as the degree of local chemical order increases. The state of local ordering also strongly correlates with the energy difference between the face-centered cubic (fcc) and hexagonal close-packed (hcp) phases, which affects the occurrence of transformation-induced plasticity. This theoretical study demonstrates that chemical short-range order is thermodynamically favored in HEAs and can be tuned to affect the mechanical behavior of these alloys. It thus addresses the pressing need to establish robust processing–structure–property relationships to guide the science-based design of new HEAs with targeted mechanical behavior.

scholarly journals Amorphization in extreme deformation of the CrMnFeCoNi high-entropy alloy

2021 ◽  
Vol 7 (5) ◽  
pp. eabb3108
Author(s):  
Shiteng Zhao ◽  
Zezhou Li ◽  
Chaoyi Zhu ◽  
Wen Yang ◽  
Zhouran Zhang ◽  
...  
Keyword(s):  
Defect Density ◽  
Amorphous Material ◽  
Stacking Faults ◽  
High Strength ◽  
High Entropy Alloy ◽  
Face Centered Cubic ◽  
Static Compression ◽  
High Entropy ◽  
High Deformation ◽  
Hexagonal Close Packed Structure

Ever-harsher service conditions in the future will call for materials with increasing ability to undergo deformation without sustaining damage while retaining high strength. Prime candidates for these conditions are certain high-entropy alloys (HEAs), which have extraordinary work-hardening ability and toughness. By subjecting the equiatomic CrMnFeCoNi HEA to severe plastic deformation through swaging followed by either quasi-static compression or dynamic deformation in shear, we observe a dense structure comprising stacking faults, twins, transformation from the face-centered cubic to the hexagonal close-packed structure, and, of particular note, amorphization. The coordinated propagation of stacking faults and twins along {111} planes generates high-deformation regions, which can reorganize into hexagonal packets; when the defect density in these regions reaches a critical level, they generate islands of amorphous material. These regions can have outstanding mechanical properties, which provide additional strengthening and/or toughening mechanisms to enhance the capability of these alloys to withstand extreme loading conditions.

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 Irradiation resistance mechanism of the CoCrFeMnNi equiatomic high-entropy alloy

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Q. Xu ◽  
H. Q. Guan ◽  
Z. H. Zhong ◽  
S. S. Huang ◽  
J. J. Zhao
Keyword(s):  
Binding Energy ◽  
High Speed ◽  
Vacancy Cluster ◽  
High Energy ◽  
Stacking Fault ◽  
High Entropy Alloy ◽  
Face Centered Cubic ◽  
High Entropy ◽  
Vacancy Clusters ◽  
Irradiation Resistance

AbstractWhen face-centered cubic (FCC) metals and alloys with low stacking fault energy (SFE) are irradiated by high-energy particles or deformed at high speed, stacking fault tetrahedra (SFTs), which are a type of vacancy cluster defect, are often formed. Therefore, SFTs were expected to form in the CoCrFeMnNi equiatomic high-entropy alloy (HEA). However, no SFT was observed in the CoCrFeMnNi HEA with high-speed plastic deformation even after annealing at 873 K. To elucidate this mechanism, the binding energy of vacancy clusters in the CoCrFeMnNi HEA was calculated based on first principles. The binding energy of the di-vacancy cluster was positive (average of 0.25 eV), while that of the tri-vacancy cluster was negative (average of − 0.44 eV), suggesting that the possibility of formation of a tri-vacancy cluster was low. The inability to form a cluster containing three vacancies is attributed to the excellent irradiation resistance of the CoCrFeMnNi HEA. However, if an extra vacancy is added to a tri-vacancy cluster (with negative binding energy), the binding energy of the subsequent tetra-vacancy cluster may become positive. This suggests that it is possible to form vacancy clusters in the CoCrFeMnNi HEA when high-energy ion or neutron irradiation causes cascade damage.

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