Microstructure of Laser-Melted Co/Co₃Mo₂Si Wear Resistant Ternary Metal Silicide Alloys

The ternary metal silicide Co₃Mo₂Si is expected to be a promising wear resistant material due to its inherent high hardness, strong anomalous hardness-temperature dependence and covalent-dominated strong atomic bonds. Poor ductility from room to intermediate high temperatures is currently the main obstacle preventing it from practical industrial applications. In order to improve the ductility of Co₃Mo₂Si ternary metal silicide, Co solid solution toughened Co₃Mo₂Si ternary metal silicide alloys were designed and fabricated by the laser melting/deposition process. As-solidification microstructure of the Co/Co₃Mo₂Si metal silicide alloys was characterized by optical microscopy (OM), X-ray diffraction (XRD), energy dispersive spectroscopy (EDS) and Vickers microhardness measurement as a function of Co content. The Co/Co₃Mo₂Si ternary metal silicide alloys have a dense and uniform microstructure consisting of the Co₃Mo₂Si primary dendrites and the interdendritic Co/Co₃Mo₂Si eutectics. Volume fraction of Co₃Mo₂Si primary dendrites (72%~92%) and the average hardness (8000 MPa~ll 000 MPa) of the alloys decrease with the increase of Co content. Compared with the single-phase Co₃Mo₂Si ternary metal silicide, the Co toughened Co₃Mo₂Si alloys have excellent balance of strength and ductility, which was attributed to the effective toughening of ductile cobalt solid solution.