Microstructure and mechanical properties of AlCoCrFeNi high entropy alloys produced by spark plasma sintering

Abstract

AlCoCrFeNi is among one of the most-widely studied alloy systems in the high entropy alloy (HEA) area. It exhibits interesting microstructure and unique mechanical properties. In this study, we assessed the feasibility of producing the AlCoCrFeNi alloy using powder metallurgy technique in which the pre-alloy powders were obtained through gas atomization and sintering was achieved by spark plasma sintering (SPS). Extensive microstructure and mechanical property characterizations were conducted to assist our understanding of the effects of processing conditions (i.e., sintering temperature) on the microstructure and mechanical properties of obtained materials. Current results indicate that powder metallurgy (in this study, gas atomization + SPS) could be used as an alternative for HEA fabrication. The pre-alloy powders exhibit microstructure (BCC + B2) similar to reported as-cast microstructure. Sintered parts with good combination of strength and compression limit (∼2368 MPa, 22.1%) can be achieved by an appropriate selection of sintering temperature (for example, 1100 °C). Similar to previous observations, temperature exerts an important role on microstructural evolution. Fully consolidated part cannot be obtained when the sintering temperature was lower than 900 °C. Sintering at 1100 °C the higher yielded parts with near-fully density can be obtained. With the increasing of sintering temperature, FCC phase depletion with Al and Ni tends to form. The network BCC phase within the B2 phase grows and gathers to the boundary of the B2 phase with the sintering temperature above 1200 °C. Further studies will be conducted to have a full picture of this microstructure behavior.