The Role of Substrate Surface Chemistry on Splat Formation during Plasma Spray Deposition by Experiments and Simulations

Abstract

Abstract 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.