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플라즈마 제트에서의 분말 용융특성에 따른 Y<sub>2</sub>O<sub>3</sub> 코팅층의 미세조직 형성거동
강상운,백경호,Kang, Sang-Woon,Baik, Kyeong-Ho 한국재료학회 2016 한국재료학회지 Vol.26 No.5
In this study, the degree of particle melting in $Y_2O_3$ plasma spraying and its effects on coating characteristics have been investigated in terms of microstructural features, microhardness and scratch resistance. Plasma sprayed $Y_2O_3$ coatings were formed using two different powder feeding systems: a system in which the powder is fed inside the plasma gun and a system in which the powder is fed externally. The internal powder spraying method generated a well-defined lamellae structure that was characterized by a thin porous layer at the splat boundary and microcracks within individual splats. Such micro-defects were generated by the large thermal contraction of splats from fully-molten droplets. The external powder spraying method formed a relatively dense coating with a particulate deposition mode, and the deposition of a higher fraction of partially-melted droplets led to a much reduced number of inter-splat pores and intra-splat microcracks. The microhardness and scratch resistance of the $Y_2O_3$ coatings were improved by external powder spraying; this result was mainly attributed to the reduced number of micro-defects.