Computational property predictions of Ta–Nb–Hf–Zr high-entropy alloys

Abstract

Refractory high entropy alloys (R-HEAs) are becoming prominent in recent years because of their properties and uses as high strength and high hardness materials for ambient and high temperature, aerospace and nuclear radiation tolerance applications, orthopedic applications etc. The mechanical properties like yield strength and ductility of TaNbHfZr R-HEA depend on the local nanostructure and chemical ordering, which in term depend on the annealing treatment. In this study we have computationally obtained various properties of the equimolar TaNbHfZr alloy like the role of configurational entropy in the thermodynamic property, rate of evolution of nanostructure morphology in thermally annealed systems, dislocation simulation based quantitative prediction of yield strength, nature of dislocation movement through short range clustering (SRC) and qualitative prediction of ductile to brittle transition behavior. The simulation starts with hybrid Monte Carlo/Molecular Dynamics (MC/MD) based nanostructure evolution of an initial random solid solution alloy structure with BCC lattice structure created with principal axes along [1 1 1], [− 1 1 0] and [− 1 − 1 2] directions suitable for simulation of ½[1 1 1] edge dislocations. Thermodynamic properties are calculated from the change in enthalpy and configurational entropy, which in term is calculated by next-neighbor bond counting statistics. The MC/MD evolved structures mimic the annealing treatment at 1800 °C and the output structures are replicated in periodic directions to make larger 384,000 atom structures used for dislocation simulations. Edge dislocations were utilized to obtain and explain for the critically resolved shear stress (CRSS) for the structures with various degrees of nanostructure evolution by annealing, where extra strengthening was observed because of the formations of SRCs. Lastly the MC/MD evolved structures containing dislocations are subjected to a high shear stress beyond CRSS to investigate the stability of the dislocations and the lattice structures to explain the experimentally observed transition from ductile to brittle behavior for the TaNbHfZr R-HEA.

Atomistic Simulations of Ductile Failure in a b.c.c. High-Entropy Alloy

“…We employed a recently developed model EAM potential for a HfNbTaZr high-entropy alloy [42]. This potential predicts a stable bcc structure for the four-component alloy and it has shown a satisfactory behavior in predicting well-known aspects of dislocations in HEAs, such as the wavy nature of the dislocation core [51]. The elastic behavior of structures with cubic symmetry is described by their elastic constants, C 11 , C 12 , and C 44 [52].…”

Strengthening from dislocation restructuring and local climb at platelet linear complexions in Al-Cu alloys

“…Since the leading and trailing partial dislocations can move at different stress levels (and indeed they always did), both critical events were isolated for each simulation variation. Such stress controlled simulations have been commonly used in literature to measure the critical shear stress for dislocation motion and/or dislocation mobility as a function of applied stress as they provide sufficient time to reach the equilibrium state and do not introduce any new defects artificially [Krasnikov et al 2020;Mishra et al 2021;Yin et al 2021].…”

Predicting Elastic Constants of Refractory Complex Concentrated Alloys Using Machine Learning Approach

“…Compared to typical superalloys, RCCAs have recently attracted increasing interest as a potential choice for high-temperature structural application materials. This is because the appealing qualities of RCCAs which include outstanding high-temperature strength, ductility, high melting temperature, and oxidation resistance [ 2 , 3 , 4 , 5 , 6 ]. The mechanical and thermodynamic properties of alloys are directly linked to their elastic constants.…”