Effect of Particle Size Distribution on Isothermal Oxidation Characteristics of Plasma Sprayed CoNi- and CoCrAlY Coatings

The effect of particle size distribution on the degradation behavior of plasma sprayed CoNi- and CoCrAlY coatings during isothermal oxidation was investigated, in terms of the oxygen content, porosity, surface roughness, and oxide scale formation. The results show that the degradation of both coatings was considerably influenced by the starting particle size distribution. It also shows that in the as-sprayed vacuum plasma spray (VPS) coatings the oxygen content on the coating surface increased significantly with decreased average particle size. But after thermal exposure, the difference of the oxygen contents between the coatings with different particle size was decreased. The powder with various particle size resulted in low porosity inside the coatings during the deposition process. The surface roughness of the coatings increased with increased particle size. The small particles produced a relatively smooth surface, and the oxide growth in the coating deposited by small particle was slower than that in the large particle coating. This article is an invited paper selected from presentations at the 2007 International Thermal Spray Conference and has been expanded from the original presentation. It is simultaneously published in Global Coating Solutions, Proceedings of the 2007 International Thermal Spray Conference, Beijing, China, May 14-16, 2007, Basil R. Marple, Margaret M. Hyland, Yuk-Chiu Lau, Chang-Jiu Li, Rogerio S. Lima, and Ghislain Montavon, Ed., ASM International, Materials Park, OH, 2007.