Entropy and diffuse scattering: comparison of NbTiVZr and CrMoNbV

TL;DR

This study compares diffuse scattering in two high entropy alloys, CrMoNbV and NbTiVZr, using simulations to understand disorder contributions and structural stability.

Contribution

It provides a detailed analysis of diffuse scattering origins and evaluates entropy reduction due to pair correlations in high entropy alloys.

Findings

Chemical disorder causes diffuse scattering in alloys.

Ti and Zr favor HCP structures at low temperature.

NbTiVZr shows reduced local BCC character due to Zr and Ti preferences.

Abstract

The chemical disorder intrinsic to high entropy alloys inevitably creates diffuse scattering in their x-ray or neutron diffraction patterns. Through first principles hybrid Monte Carlo/molecular dynamics simulations of two BCC high entropy alloy forming compounds, CrMoNbV and NbTiVZr, we identify the contributions of chemical disorder, atomic size and thermal fluctuations to the diffuse scattering. As a side benefit, we evaluate the reduction in entropy due to pair correlations within the framework of the cluster variation method. Finally, we note that the preference of Ti and Zr for HCP structures at low temperature leads to a mechanical instability reducing the local BCC character of NbTiVZr, while preserving global BCC symmetry.