C. Moreau, National Research Council Canada (CNRC-NRC), Boucherville,, QC, Canada; A. McDonald, University of Toronto, Toronto, ON, Canada; M. Lamontagne, Industrial Materials Institute, National Research Council Canada, Boucherville, QC, Canada; S. Chandra, Centre for Advanced Coating Technology, University of Toronto, Toronto, ON, Canada
Plasma-sprayed, molten nickel particles (60 µm diameter) were photographed during impact on 304L stainless steel surfaces that were maintained at room temperature or at elevated temperatures to promote growth of an oxide layer. Droplets approaching the surface were sensed using a photodetector and after a known delay, a fast CCD camera was triggered to capture integrated images of the spreading splat from the substrate front surface. A rapid two-color pyrometer was used to collect the thermal radiation from the impacting particles to follow the evolution of their temperature after impact.
Molten nickel particles impacting on surfaces at room temperature fragmented, after achieving a maximum diameter larger than 300 µm. Impact on stainless steel heated for short time intervals produced splats with smaller maximum diameters and with disk-like morphologies. Splats on surfaces exposed to prolonged heating were small and had pancake-like morphologies, with finger-like splash projections at the periphery. The oxide layers on these surfaces were also significantly larger. The cooling rate of splats on the oxidized surfaces was larger than that of splats on non-heated steel, suggesting that the splat-substrate contact was improved and played a role in the occurrence of splashing.
Summary: Plasma-sprayed nickel particles were photographed during impact on stainless steel surfaces that were maintained at room temperature or at elevated temperatures to promote growth of an oxide layer. The molten particles impacting on surfaces at room temperature fragmented, after achieving a maximum diameter larger than 300 µm. Impact on stainless steel heated for short time intervals produced splats with smaller maximum diameters and with disk-like morphologies. Splats on surfaces exposed to prolonged heating were small and had pancake-like morphologies, with finger-like splash projections at the periphery. The oxide layers on these surfaces were also significantly larger. The cooling rate of splats on the oxidized surfaces was larger than that of splats on non-heated steel, suggesting that the splat-substrate contact was improved and played a role in the occurrence of splashing.
