Influence of WC content on microstructure and mechanical properties of Mo2FeB2-based cermets fabricated by multi-step sintering

Abstract

Herein, Mo2FeB2-based cermets, with nominal composition of Mo2FeB2-2.06Fe-2.9Ni-2.5Cr-xWC-0.04C (x = 0, 2.5, 5, 10 wt %), are fabricated by multi-step sintering to investigate influence of tungsten carbide (WC) content on microstructure and mechanical properties. Results reveal that the microstructure of WC-free cermets resembles that of traditional cermets. However, microstructure of WC-containing cermets (x = 2.5 wt %) is composed of fine black core/grey rim Mo2FeB2 grains and coarse white-colored coreless Fe3(W,Mo)3C grains. Furthermore, at x ≥ 5 wt %, most of white coreless Fe3(W,Mo)3C grains are transformed into a white core/black rim structure. From these observations, it can be concluded that growth of nearly round-shaped Mo2FeB2 grains is through diffusion-control, leading to normal grain growth (NGG), whereas the growth of polyhedral Fe3(W,Mo)3C grains is dictated by the interfacial reactions, resulting in 2D nucleation and partially abnormal grain growth (AGG). In addition, grain size distribution of WC-containing cermets exhibits distinct bimodal characteristics, where average grain size is smaller than that of WC-free cermets. More importantly, presence of WC significantly improves the mechanical properties, resulting in superior fracture toughness of 25.1 ± 0.5 MPa m1/2 and hardness of 90.3 ± 0.1 HRA, at x = 5 wt %, without compromising much of transverse rupture strength.