Phase composition and microstructure of WC–Co alloys obtained by selective laser melting

Abstract

Phase composition and microstructure of initial WC, BK8 (powder alloy 92 wt.% WC–8 wt.% Co), Co powders, ball-milled powders with four different compositions (1) 25 wt.% WC–75 wt.% Co, (2) 30 wt.% BK8–70 wt.% Co, (3) 50 wt.% WC–50 wt.% Co, (4) 94 wt.% WC–6 wt.% Co, and bulk alloys obtained by selective laser melting (SLM) from as-milled powders in as-melted state and after heat treatment were investigated by scanning electron microscopy and X-ray diffraction analysis. Initial and ball-milled powders consist of WC, hexagonal α-Co and face-centered cubic β-Co. The SLM leads to the formation of major new phases W3Co3C, W4Co2C and face-centered cubic β-Co-based solid solution. During the heat treatment, there occurs partial decomposition of the face-centered cubic β-Co-based solid solution with the formation of W2C and hexagonal α-Co solid solution. The microstructure of obtained bulk samples, in general, corresponds to the observed phase composition.