Microstructure development and mechanical properties of nickel matrix/carbide composites

Nickel alloy matrix/dispersed carbide (VC, NbC, WC) composites were prepared by either flame-spray, liquid phase sintering, or solid state sintering. A commerical Ni-B-Si alloy was mixed with 15 vol.% of carbide particles and used to prepare composite coatings by flame-spray, bulk composite materials by solid state sintering ( < 1045 deg C) or liquid phase sintering ( > 1050 deg C). Phase characterization was performed by x-ray diffraction, optical microscopy, scanning electron microscopy and x-ray fluroescence in energy and wavelength dispersive spectroscopy modes. Similar microstructural features were produced by thermal spray and liquid phase sintering: a Ni-rich matrix and a boron-rich intergranular phase. Sintered samples showed higher wear resistance than the coatings obtained by flame spraying. In both cases the wear mechanism is dominated by the plastic flow of the Ni-rich ductile matrix and the fracture of a boron-rich intergranular phase, the latter serving as a retainer. Carbide removal was observed for solid state sintered samples.