Ab-initio tensile tests applied to BCC refractory alloys

TL;DR

This study uses ab-initio tensile simulations to analyze the deformation and ductility of Nb- and Mo-based refractory alloys, revealing how peak stress correlates with valence electron count and physical properties.

Contribution

It introduces direct ab-initio tensile testing for refractory alloys, providing insights into deformation mechanisms and ductility prediction based on electronic structure.

Findings

Peak stress increases with valence electron count.

Deformation involves slip, stacking faults, transformation, and twinning.

Correlations found among physical properties and ductility parameters.

Abstract

Refractory metals exhibit high strength at high temperature, but often lack ductility. Multiprinciple element alloys such as high entropy alloys offer the potential to improve ductility while maintaining strength, but we don't know $a-priori$ what compositions will be suitable. A number of measures have been proposed to predict the ductility of metals, notably the Pugh ratio, the Rice-Thomson D-parameter, among others. Here we examine direct $ab-initio$ simulation of deformation under tensile strain, and we apply this to a variety of Nb- and Mo-based binary alloys and to several quaternary alloy systems. Our results exhibit peak stresses for elastic deformation, beyond which defects such as lattice slip, stacking faults, transformation, and twinning, relieve the stress. The peak stress grows strongly with increasing valence electron count. Correlations are examined among several physical properties, including the above-mentioned ductility parameters.