A nanocrystalline AlCoCuNi medium-entropy alloy with high thermal stability via entropy and boundary engineering

A promising strategy involving the synergetic effects of the high-entropy engineering and interface architectures has been proposed to realize the thermal stability of nanocrystalline alloys. A bulk dual-phase nanocrystalline (DPNC-) AlCoCuNi medium-entropy alloy was prepared by mechanical alloying (MA) and spark plasma sintering (SPS) process. These DPNC structures include Cu-rich and AlCoNi-rich nanocrystallines (NCs) with an average grain size of 46 nm. This DPNC-AlCoCuNi material could maintain the nanostructures as well as a high hardness of about 580 HV even after annealing at 900 °C for 50 h. The extremely high thermal stability has been attributed to the extensive thermal-stabled low-energy phase boundaries, low-angle grain boundaries, the high-entropy and sluggish diffusion effects.