Rapid Down-Selection of Novel High-Entropy Materials and Insights into their Characteristic Energy Scales from Temperature-Dependent Elastic Properties

High-entropy materials have generated much interest owing to their exceptional performance and high tunability. However, there are significant challenges in optimizing high-entropy compositions for tailored applications, such as in nuclear reactors, stemming from the immense size of the high-entropy design space. There is a pressing need for rapid, quantitative property assessments to identify promising high-entropy candidates, down-select compositions for further study, and provide experimental inputs to facilitate model development. One enticing property to examine in this context is elasticity. Elastic constants describe the extent to which materials resist elastic deformation, providing important information on mechanical performance as well as microscopic details about the nature of bonding and characteristic energy scales in materials. These features mean elastic constants naturally connect experiment and theory, making them prime candidates to serve as a benchmark for materials design, model development, and model validation.<br/><br/>In this talk, I will share elastic constant measurements on a range of refractory high-entropy alloys at ambient conditions to exemplify how elastic constants and ultrasonic attenuation can be used to rapidly identify promising high-entropy compounds for further study. Then, I use elastic constant determination down to 2K to explore the effects of composition on characteristic phonon energy scales (<i>e.g.</i>, Debye temperature), anharmonicity, and mechanical performance. These results are compared with theoretical predictions. Resonant ultrasound spectroscopy (RUS) is used for these experiments because of its ability to non-destructively determine the entire elastic constant tensor from a single measurement with high accuracy and precision. This approach, which entails extracting elastic constants from mechanical resonant frequencies, is amenable to all high-entropy materials, from metals to ceramics, compatible with any amount of crystalline anisotropy or texture, and capable of providing rapid feedback on novel high-entropy materials. As such, elastic constant determination with RUS is ideal to rapidly identify promising high-entropy materials, examine their functional properties, and determine key energy scales to incorporate in predictive models.