Determination of Local Short-Range Order in TiVNbHf(Al)

TL;DR

This study employs advanced microscopy and statistical methods to directly identify and quantify short-range chemical order in TiVNbHf(Al) alloys, revealing significant local order and its enhancement with Al addition.

Contribution

It introduces a novel approach combining aberration corrected STEM and spatial statistics to quantify nanoscale short-range order in complex alloys.

Findings

Deviations from random and fully ordered distributions confirmed.

Local chemical order identified in TiVNbHf alloys.

Al addition enhances short-range order.

Abstract

The presence of short-range chemical order can be a key factor in determining the mechanical behavior of metals, but directly and unambiguously determining its distribution in complex concentrated alloy systems can be challenging. Here, we directly identify and quantify chemical order in the globally single phase BCC-TiVNbHf(Al) system using aberration corrected scanning transmission electron microscopy (STEM) paired with spatial statistics methods. To overcome the difficulties of short-range order (SRO) quantification with STEM when the components of an alloy exhibit large atomic number differences and near equiatomic ratios, 'null hypothesis' tests are used to separate experiment from a random chemical distribution. Experiment is found to deviate from both the case of an ideal random solid solution and a fully ordered structure with statistical significance. We also identify local chemical order in TiVNbHf and confirm and quantify the enhancement of SRO with the addition of Al. These results provide insights into local chemical order in the promising TiVNbHf(Al) refractory alloys while highlighting the utility of spatial statistics in characterizing nanoscale SRO in compositionally complex systems.