HVOF Fuel Chemistry Effects on Particle Parameters and Coating Attribute Implications

Understanding the complex, in-flight dynamics of thermally sprayed particles is fundamental to determine resultant coating properties. Specifically, the in-flight oxidation states of metallic and cermet materials play a key role in all facets of the coating itself, and this has been a topic of rigorous study for the past several decades. While much work has been done regarding the in-flight oxidation of HVOF powders, the exploration of this phenomenon’s effect at various standoff distances and oxygen-to-fuel ratios is of interest. This paper attempts to relate process diagnostics at common standoff distances with changes in oxidation. This relationship is then used to theorize the various mechanisms occurring in the complex dynamics that occur during particle flight. Using in-flight process diagnostic tools, an analysis of spray distance and oxygen-to-fuel ratios on the oxidation state of a variety of thermal spray powders was conducted. Examples of this study for tungsten carbide and chromium carbide powders will be presented, along with MCrAlY and nickel alloy powders.