Diffusion in High Entropy Alloy Systems – A Review

High entropy alloys (HEAs) represent a class of multicomponent alloys that have garnered significant attention within materials community over the past two decades, largely due to their potential for high-temperature applications. It is essential to comprehend the diffusion behavior within these systems as it forms the foundational basis for designing and developing materials for specific uses, especially in high-temperature applications where the sluggish diffusion effect plays a pivotal role in enhancing material properties. Nevertheless, the existence and extent of the sluggish diffusion effect in these materials have been vigorously debated. Our understanding of this effect in HEAs remains limited, primarily because practical techniques for determining multicomponent diffusion behavior are lacking. This is also the reason that the data on diffusion in quaternary and higher-order systems are scarce in the literature. This review provides an overview of the present state-of-the-art in diffusion studies within the context of HEAs and explores the potential methodologies. Although the existence of sluggish diffusion in HEAs has been a topic of intense debate, there is currently insufficient experimental evidence to support its presence. Consequently, the review explores potential future research directions that aim to fill the gaps in our understanding of this area.