In situ development and high temperature features of CoCrFeNi-M6 Cp high entropy-alloy based hardmetal

Abstract

In this work, an in-situ CoCrFeNi-M6 Cp high entropy-alloy (HEA) based hardmetal with a composition of Co25 Cr21 Fe18 Ni23 Mo7 Nb3 WC2 was fabricated by the powder metallurgy (PM) method. Microstructures and mechanical properties of this HEA were characterized and analyzed. The results exhibit that this HEA possesses a two-phase microstructure consisting of the face-centered cubic (FCC) matrix phase and the carbide M6 C phase. This HEA has an average grain size of 2.2 µm, and the mean size and volume fraction of carbide particles are 1.2 µm and 20%. The tensile tests show that the alloy has a yield strength of 573 MPa, ultimate tensile strength of 895 MPa and elongation of 5.5% at room temperature. The contributions from different strengthening mechanisms in this HEA were calculated. The grain boundary strengthening is the dominant strengthening mechanism, and the carbide particles are significant for the further enhancement of yield strength by the dislocation strengthening and Orowan strengthening. In addition, with increasing temperatures from 600°C to 900° C, the HEA shows a reduced yield strength (YS) from 473 MPa to 142 MPa, a decreased ultimate tensile strength (UTS) from 741 MPa to 165 MPa and an enhanced elongation from 10.5% to 31%.