The influence of diamond addition to Ni-Al powder on oxidation behavior of NiAl during plasma spraying for high performance oxide-free Ni-Al intermetallic coating

Although Ni-Al intermetalics are the excellent corrosion and oxidation resistant materials, their oxidation during thermal spraying has limited the applications as coatings. 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 within plasma-sprayed Ni-Al coatings by introducing diamond as deoxidation source in Ni-Al composite powder during plasma spraying. Ni-Al coatings were plasma-sprayed with Ni-Al-Diamond composite powders 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 adhesion strength of the coatings were characterized by X-ray diffraction, scanning electron microscopy, image analyzing and tensile test. The oxygen content of the coatings was measureed quantitatively. The results show that APS Ni-Al coating with Ni-Al-diamond powders presents significantly lower oxygen content less than 0.5 wt%. The measurement yields particle temperatures higher than 2300^oC. The low oxygen content in the coating is attributed to the in-situ deoxidation effect of ultra-high temperature carbon-contained droplets. Moreover, the Ni-Al coatings are also featured with less porosity and higher tensile strength than the conventional Ni-Al coatings.