Characterization of High-Velocity Oxygen Fuel and Shrouded Plasma Sprayed Cr3C2-CoNiCrAlY Coatings: Feedstock, As-Sprayed, and Equilibrium Heat-Treated Coatings

This research examines the combination of a corrosion-resistant CoNiCrAlY binder with Cr3C2 carbide particles. The powder was applied using two contrasting thermal conditions: low-energy HVOF and high-energy shrouded plasma spraying. This approach created a wide range of carbide dissolution and peritectic decomposition outcomes. The study includes detailed characterization of the feedstock powder composition to explain the phase formation during sintering compared to the original powder components.

Conventionally, Cr3C2 based composite thermal spray coatings have been applied with a NiCr binder. This work investigates the use of a more corrosion resistant CoNiCrAlY binder phase with Cr3C2 carbide particles. The powder was sprayed under low, and extremely high, thermal input conditions using HVOF and shrouded plasma spraying respectively, to generate a broad distribution in the extent of carbide dissolution and peritectic decomposition. In this work the feedstock powder composition is characterised in detail to justify the phases formed during sintering, relative to those of the starting individual powder components. The phase transitions generated under low and high thermal input spraying conditions are characterised in the as-sprayed coatings, with the mechanisms of formation discussed. These compositions are then contrasted with those formed following high temperature heat treatment, which was assumed to enable the composition to reach equilibrium, to assess the effect of in-flight carbon loss on the steady state coating composition.