Predicting interstitial elements in Refractory Complex Concentrated Alloys

TL;DR

This paper combines experimental and computational methods to understand oxygen interstitial behavior in refractory complex concentrated alloys, aiming to improve their high-temperature mechanical performance.

Contribution

It introduces a combined experimental-computational framework to predict oxygen solubility and behavior in RCCAs, aiding in alloy design for better mechanical properties.

Findings

Oxygen solubility limit identified between 0.8-1.0 atomic percent.

HfO2 formation occurs beyond the oxygen solubility limit.

Machine-learning potentials effectively model oxygen interactions at the atomic scale.

Abstract

Refractory complex concentrated alloys, composed of multiple principal refractory elements, are promising candidates for high-temperature structural applications due to their exceptional thermal stability and high melting points. However, their mechanical performance is often compromised by interstitial impurities, particularly oxygen, nitrogen, and carbon, which segregate to grain boundaries and promote embrittlement. In this study, we investigate the solubility and thermodynamic behavior of oxygen interstitials in a model NbTiHfTa RCCA system. We synthesized NbTiHfTa alloys with varying oxygen contents via plasma arc melting and characterized their phase evolution and microstructure using XRD, SEM, and TEM. Complementary computational modeling was performed using machine-learning interatomic potentials integrated with Monte Carlo simulations to probe oxygen interactions at the atomic scale. Our results reveal a solubility limit for oxygen between 0.8 and 1.0 atomic percentage, beyond which HfO2 formation is energetically favorable. This combined experimental-computational framework provides a predictive approach for managing interstitial behavior in RCCAs, enabling improved alloy design strategies for enhanced mechanical performance.