Processing, microstructure and properties of Ni1.5CoCuFeCr0.5−xVx high entropy alloys with carbon introduced from process control agent

Abstract

Ni1.5CoCuFeCr0.5−xVx (x = 0.25, 0.5 mol) high entropy alloys (HEAs) have been prepared by mechanical alloying (MA) and spark plasma sintering (SPS). During MA, a small amount of carbon has been introduced from the decomposition of process control agent into the HEAs. Phase composition, microstructure and mechanical properties of the alloys were studied systematically. During MA process, FCC and BCC structured supersaturated solid solutions were formed in the HEA powders. After SPS, BCC phase in the MA state disappeared, while two FCC phases (named FCC1 and FCC2) and minor carbides were observed in the bulk HEAs. The carbides in the consolidated Ni1.5CoCuFeCr0.25V0.25 and Ni1.5CoCuFeV0.5 alloys were identified as (V,Cr)7C3 and V2C phases, respectively. Moreover, these carbides with the average grain diameter of about 130 nm were dispersively distributed in the ultra-fine grained FCC structured matrix phase. The as-sintered Ni1.5CoCuFeCr0.25V0.25 and Ni1.5CoCuFeV0.5 alloys exhibited compressive yield strength of 1045 and 1130 MPa, respectively, and they were not fractured under compression. The excellent comprehensive compressive mechanical properties of the bulk HEAs were associated with the appropriate amount of carbon incorporation as well as the combined effect of multiple strengthening mechanisms.