INFLUENCE OF SUBSTRATE PREPARATION ON THE FLATTENING AND COOLING OF PLASMA-SPRAYED PARTICLES

Impacts of plasma-sprayed molybdenum particles were monitored by detecting thermal radiation emitted by the hot particles when they flatten on the substrate surface. Evolution of the light intensity collected at two different wavelengths was used to obtain information about flattening time, flattening degree, and cooling time of the impinging particles, Variations of these parameters with substrate surface roughness were investigated on glass and molybdenum substrates. The substrate roughness significantly influenced the flattening degree and flattening time of the particles: the smoother the substrate, the larger the surface of the splats and the longer the flattening time, The cooling time, as determined from the decay time of the light signals after impact, was shorter on smooth substrates, In this case, the temperature of the splats was not radially uniform, with a lower cooling rate at the periphery.