A comprehensive guide to high-entropy alloy subgroups

Despite the fact that numerous equiatomic and nonequiatomic high-entropy alloys (HEAs) have been observed to form a single solid solution (SS), it has also been established that several intermediate phases can emerge, some of which exhibit the structural characteristics of intermetallic compounds (ICs) such as Laves, B2, sigma, L12, and amorphous phases. This phenomenon has been extensively documented by researchers, and it is primarily attributed to a range of competing factors, including the mixing enthalpy, mixing entropy, and disparities in atomic sizes among the constituent elements present in these HEAs. Despite the fact that numerous equiatomic and nonequiatomic HEAs have been observed to form a single SS, it has also been established that several intermediate phases can emerge, some of which exhibit the structural characteristics of ICs such as Laves, B2, sigma, L12, and amorphous phases. This phenomenon has been extensively documented by researchers, and it is primarily attributed to a range of competing factors, including the mixing enthalpy, mixing entropy, and disparities in atomic sizes among the constituent elements present in these HEAs. HEAs have significantly expanded the available composition space for the design and fabrication of alloys. Consequently, it is of great importance to rigorously classify HEAs according to their component constituents. The principal categories encompass transition metal (TM) HEAs, refractory HEAs (RHEAs), lightweight HEAs, and HE-bulk metallic glasses. Among these, the most extensive class of HEAs consists of TMs, and these HEAs display an extensive array of chemical components, microstructures, and properties, allowing for additional subclassification. In contrast, RHEAs are composed of refractory elements with high melting points, primarily designed for use in high-temperature applications. The development of HEAs, such as lightweight HEAs, introduces new challenges, and prospects in the realm of advancing materials for critical applications. As a result, this chapter aims to offer a comprehensive overview of subgroups, intermetallic, and amorphous phases, and the impact of interstitial elements that have been investigated in various types of HEAs. © 2024 Elsevier Inc. All rights are reserved including those for text and data mining AI training and similar technologies.