Study of the splat formation for plasma sprayed NiCr on aluminum substrate as a function of substrate condition

The study of splat formation, splat-substrate interactions and the influence of the substrate surface conditions on splat behavior is a key step in understanding and improving the plasma spray process. In the present work, NiCr particles were plasma sprayed onto aluminum substrates to form single splats, and their microstructure, along with the splat-substrate interface, was studied using a range of microscopy techniques (SEM, FIB, TEM and AFM). From the observations made, a model summarizing the splat formation process has been proposed. Substrates with various surface conditions, induced by heating and/or boiling treatment prior to spraying, were used. It was observed that on the non-boiled specimens, the contact between splat and substrate was poor, possibly due to the desorption of adsorbates/condensates present on the substrate surface, and no splats were formed on the boiled specimens, due to the presence of a thick hydroxide layer.