In this work, a mechanically clad NiCr powder feedstock was deposited on alumina substrates by atmospheric plasma arc spraying. The resultant splats were analyzed for features such as interfacial bonding, splat classification and, critically, Cr distribution. Using a slice-and-view sectioning technique in a dual-beam FIB-SEM system, a representative splat exhibiting discrete Ni and Cr regions was physically deconstructed then reconstructed with visualization software to analyze individual layers with the splat. Although the powder feedstock contained Ni particles clad with clusters of Cr, the splats solidified into distinct layers of Ni and Cr with no signs of interaction between them. A model formulated based on this observation shows that the distribution of Cr cladding on the Ni particulates influences the amount and location of Cr around the solidified Ni splats.

NiCr was plasma sprayed at room temperature on aluminum and stainless steel substrates that had been hydrothermally treated in deionized water for 30 minutes. A major difference was observed in that splat formation occurred only on the stainless steel. A numerical model was developed to simulate the impact of molten nickel splats on the treated substrates. The simulation closely matched experimental results in terms of splat morphology, porosity, delamination, and specific locations of substrate melting. Moreover, it confirmed that splat morphology is influenced, not by oxide thickness, but rather by water release from the dehydration of oxyhydroxide at the outermost surface. The insulating layer of released water inhibits heat transfer from the splat to the substrate, which reduces solidification rates, resulting in further spreading and thinning of splats. These findings shed light on splat spreading and solidification and provide insights on the effect of substrate surface chemistry on thermal spray splat morphology.