The Influence of Diamond Addition to Ni-Al Powder on Oxidation Behavior of Ni-Al During Plasma Spraying for High Performance Ni-Al Intermetallic Coating

Although Ni-Al intermetallics are of excellent corrosion and oxidation resistance, their oxidation during thermal spraying limits the applications as thermal spray coating. Thus, controlling the oxidation is a necessary approach to improve their performances as the coatings. In this study, a novel approach is proposed to exclude oxide of in-flight Ni-Al droplets by introducing diamond as a deoxidizer in Ni/Al powder during plasma spraying. Ni-Al coatings were deposited with Ni/Al/diamond composite powder prepared by mechanical alloying by atmospheric plasma spraying at different spray conditions to study the effect of the diamond addition on the oxidation behavior of in-flight droplets. The phase composition, microstructure, porosity and microhardness of the coatings were characterized by X-ray diffraction, scanning electron microscopy, image analyzing and hardness test, respectively. The oxygen content of the coatings was measured quantitatively. The results show that APS Ni-Al coating prepared by Ni/Al/diamond powder presents significantly lower oxygen content. The measurement yields particle temperatures higher than 2300^oC. The low oxygen content in the coating is attributed to the in-situ deoxidizing effect of ultra-high temperature contained droplets. Moreover, the oxide-free droplets promote the deposition of Ni-Al coatings with lower oxygen content and porosity than the conventional Ni-Al coatings.