Phase characterization in Ni alloy-hard carbide composites for fused coatings

Abstract

Ni-based alloys containing low amounts of boron and silicon, reinforced with hard carbides, are extensively used for wear-resistant coatings. A powdered alloy of NiBSi and two of NiCrBSi (with 10.5 and 15 wt.% Cr, respectively) were mixed with VC and WC in proportions of 15 and 50 vol.% and then processed by either thermal spraying or liquid phase sintering. Phase identification was performed by X-ray diffraction (XRD), scanning and transmission electron microscopy (SEM and TEM), and energy and wavelength dispersion spectroscopy (EDS and WDS). Materials free of Cr and those containing 10.5% Cr were characterized by the presence of a boron-rich net. At 15% Cr, the distribution of the boron-rich phase was sensibly modified. Further, Cr addition produced finely dispersed carbides with variable contents of V or W. Vanadium diffusion in the matrix, as well as metal interchange between vanadium and chromium carbides is, apparently, enhanced by increasing Cr content. Mass transfer processes in carbide-matrix interface seems to be slower when WC is used as reinforcement.