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

TL;DR

This study computationally investigates the properties of Ta-Nb-Hf-Zr high-entropy alloys, focusing on nanostructure evolution, thermodynamics, dislocation behavior, and ductile-brittle transition, providing insights into their mechanical performance.

Contribution

It introduces a hybrid MC/MD simulation approach to predict nanostructure, thermodynamic properties, and dislocation dynamics in Ta-Nb-Hf-Zr R-HEAs, advancing understanding of their mechanical behavior.

Findings

Configurational entropy influences thermodynamic stability.

SRC formations contribute to alloy strengthening.

Dislocation stability relates to ductile-brittle transition.

Abstract

Refractory high entropy alloys (R-HEAs) are having 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. In this study we have computationally obtained various properties of the 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 1/2[1 1 1] edge dislocations. Thermodynamic properties are calculated from the change in enthalpy and the configurational entropy by next-neighbor bond counting statistics. The MC/MD evolved structures mimic the annealing treatment at 1800{\deg}C and the output structures are replicated in periodic directions to make larger 384000 atom structures used for dislocation simulations. Edge dislocations were utilized to obtain and explain for the extra strengthening 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.