Plasma-sprayed nickel and molybdenum particles (∼55 μm diameter) were photographed during spreading on silicon wafers that
were patterned with micron-sized columns to make a textured rough surface. Impact on grit-blasted glass was also studied.
The surfaces were maintained at either room temperature or at 350 °C. As the droplets approached the surface they were sensed
by a photodetector and, after a known delay, a fast charge-coupled device (CCD) camera was triggered to capture time-integrated
images of the spreading splat. A rapid two-color pyrometer was used to collect the thermal radiation from the spreading particles
to record the evolution of their temperature and calculate splat cooling rates. It was found that micron-sized columns on
the textured surfaces impeded fluid flow during spreading of splats, promoting splashing. When the column height was on the
order of the splat thickness, increasing the space between each column increased the splat cooling rate as the columns penetrated
into the liquid splat, providing a larger surface area for heat transfer. On the grit-blasted glass surfaces it was found
that as the surface roughness increased, the maximum spread diameters of the molten droplets decreased, while the splat cooling
rates increased. Impact on non-heated and heated roughened glass with similar roughness values produced splats with approximately
the same maximum spread diameters, skewed morphologies, and cooling rates. On smooth glass, the splat morphologies were circular,
with large maximum spread diameters and smaller cooling rates on non-heated smooth glass. An established model was used to
estimate the splat-substrate thermal contact resistances. On highly roughened glass, the thermal contact resistance decreased
as the glass roughness increased, suggesting that splat-substrate contact was improved as the molten metal penetrated the
spaces between the large asperities.