Microstructure and mechanical properties of Mo2FeB2-316SS cermets prepared by vacuum sintering

Abstract

Mo₂FeB₂-316 stainless steel (316SS) cermets with varying Mo₂FeB₂ powder contents (69.5, 75, 80.5, wt%) were prepared. The Mo₂FeB₂ powder was first synthesized at 1000 ℃ for 1 h by reaction between ultrafine Mo powder and FeB powder, and then mixed with 316SS powder to prepare the Mo₂FeB₂-316SS cermets via vacuum sintering at different temperatures. The results revealed that in the cermets, some black near-spherical particles existed at the interface of the Mo₂FeB₂ hard phase and Fe binder phase due to the oxidations of Si and Mn elements introduced through FeB and 316SS powders. The presence of Si-Mn complex oxides reduced the interfacial wettability and thereby increased porosity, which deteriorated the hardness and transverse fracture strength. Whereas, it improved the fracture toughness through crack bridging and pinning effect. The cermet with 80.5 wt% Mo₂FeB₂ power, sintered at 1200 ℃, achieved superior comprehensive properties with Vickers hardness of 1258 HV₃₀, transverse rupture strength (TRS) of 1735.9 MPa and fracture toughness (K_IC) of 17.5 MPa·m^1/2. As the temperature increased, the hardness, fracture toughness and transverse rupture strength decreased. The growth of abnormal grains was the main reason, which was related to a two-dimensional nucleation mechanism.