Production of high-density Ni-bonded tungsten carbide coatings using an axially fed DC-plasmatron

Using an axial feed DC-plasmatron, mixtures of fine Ni and WC powder (1–3 μm) were plasma sprayed onto stainless steel substrates. A series of high-density Ni–WC coatings were produces with uniform distribution of WC particles. The small powder sizes coupled with the axial feed system resulted in high vaporization rates of the Ni and significant decomposition of the WC powders. The high vaporization rate of Ni followed by condensation contributes to the high density of the coatings, while the high WC decomposition rate results in low WC content and low hardness values of the coatings. Based on published data and simple energy balance equations, evaporation of as much as 20% of the Ni powder was estimated, and XRD analysis indicates decomposition of as much as 80% of the WC particles.