Effect of substrate temperature and roughness on the solidification of copper plasma sprayed droplets

Flattening of an individual thermal sprayed particle on the substrate is a fundamental process for the coating formation. Coating properties such as porosity and adhesion depend strongly from the splats morphology. Also, the microstructure of the coating depends on the nucleation and the grain growth during splats solidification. The influence of the substrate temperature and roughness on the microstructure of copper splats was examined in the present study. Copper (−90 + 45 μm) was plasma sprayed under atmospheric conditions on mirror polished (Ra ∼ 0.02 μm) and on grit-blasted (Ra ∼ 1.33 μm) stainless steel substrates (AISI 304L). The substrates were preheated at three different temperatures: 200 °C, 250 °C and 300 °C. A Schottky field emission scanning electron microscope (SFE-SEM) was used in order to study the splats microstructure. In order to measure the grain size of the splats, image analysis software was used, while the chemical composition of the splats was studied by an electron probe microanalysis (EPMA). It was found that the splats cooling velocity is decreased with the increase of substrate temperature above the transition temperature. Also a further decrease of splats cooling velocity was provoked by increasing the mean substrate roughness.