Surface roughness characterization of thermally sprayed and precision machined WC–Co and Alloy-625 coatings

Surface roughness characterization of thermally sprayed and precision machined WC–Co and Alloy-625 coatings was carried out. The objectives were to demonstrate that such difficult-to-machine coating surfaces could be machined with commercial machines and tools, and to characterize the surface finish of the machined coatings. The coatings were obtained using two thermal spraying processes: arc spraying and high velocity oxy-fuel spraying. Different machining techniques were tried to optimize the surface finishing of the coatings based on surface finish and time required. Machined samples were then examined using stylus roughness testers. Surface roughness parameters Ra and Rq were measured using various cut-off lengths, sampling lengths, and numbers of sampling and cut-off lengths to characterize the scaling behavior of the surfaces. Diamond turning of WC–Co demonstrated the advantage of high material removal rates, and diamond grinding of WC–Co produced good surface finish with relatively high material removal rates. Precision-machined WC–Co and Alloy-625 surfaces could be identified as self-affine fractals in a statistical sense within the correlation length, i.e. within the length scales studied from 0.08 to 8 mm. The surface roughness heights of the machined surfaces were found to be dependent on the scale of cut-off length as a power law.