High-entropy alloys and metallic nanocomposites: Processing challenges, microstructure development and property enhancement

Abstract

Two classes of new materials, i.e. high entropy alloys (HEAs) and metallic nanocomposites offer processing related challenges, while showing significant promise for an array of technological applications requiring wear and irradiation resistance. This review addresses those challenges together with microstructure-property correlations. In particular, the main focus of this review is to demonstrate the efficacy of the superfast densification route, i.e., spark plasma sintering (SPS) as an effective consolidation route for these two classes of materials.To start with, this review will critically analyze the influence of conventional solidification on the microstructure and property of Cu-based bearing alloys. Using nanocrystalline Cu-Pb and Cu-Pb-TiB2, Cu-Pb-cBN (cubic boron nitride) as model systems, various aspect of the microstructure-property correlation and enhancement of the tribological properties will be highlighted. A thorough understanding of the processing related issues and stability of the nanoscale/ultrafine microstructure obtained via SPS will be illustrated.A significant part of this review will further discuss the development of novel nanostructured HEAs and HEA-based composites for wear and irradiation resistance applications. The efficacy of SPS route to prepare bulk HEAs with high sinter density will be demonstrated, together with property enhancement in single phase and two-phase HEAs. HEA-based nanocomposites containing soft metallic dispersoids (Bi, Pb, Ag) and ceramic lubricating phases (MoS2, CaF2/BaF2) for wear resistance application will be highlighted. Finally, oxide dispersed and refractory HEAs via MASPS route for irradiation resistance application will be discussed to elucidate the effective usage of the design and development of HEAs for technologically critical applications.