Powder interface modification for synthesis of core-shell structured CoCrFeNiTi high entropy alloy composite

Abstract

Interface design is a critical topic for development of multifunctional materials. In an effort to achieve novel microstructural materials, we synthesized CoCrFeNiTi-TiN high entropy alloy composite with core-shell microstructure using powder metallurgy process. Initially single phase CoCrFeNiTi0.5 powder with BCC crystal structure was obtained using mechanical alloying process. Afterwards alloyed powder was heat treated at 900 °C under partial pressure ratios (PN2/PAr) of 1.00, 0.67, 0.33 and 0.10. During the heat treatment the powders mainly consisted of FCC, CrN and TiN phases. At higher values of PN2/PAr, the CrN and TiN phase was were present throughout the powder. By decreasing the PN2/PAr value, nitride precipitation was confined at the powder interfaces. PN2/PAr = 0.10 was the optimum atmosphere conditions where a distinct core-shell structure was formed. At this condition, TiN made up the shell while rest of the elements formed the core. Finally, core-shell powder was consolidated using spark plasma sintering (SPS) to achieve a bulk with core-shell microstructure. This fabrication method reveals a promising avenue to achieve multifunctional high entropy alloys.