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J. Korean Ceram. Soc. > Volume 52(6); 2015 > Article
Journal of the Korean Ceramic Society 2015;52(6): 410.
doi: https://doi.org/10.4191/kcers.2015.52.6.410
Residual Stress and Elastic Modulus of Y2O3 Coating Deposited by EB-PVD and its Effects on Surface Crack Formation
Dae-Min Kim, Yoon-Soo Han, Seongwon Kim, Yoon-Suk Oh, Dae-Soon Lim1, Hyung-Tae Kim, Sung-Min Lee
Engineering Ceramic Team, Korea Institute of Ceramic Engineering and Technology
1Department of Materials Science and Engineering, Korea University
Recently, a new $Y_2O_3$ coating deposited using the EB-PVD method has been developed for erosion resistant applications in fluorocarbon plasma environments. In this study, surface crack formation in the $Y_2O_3$ coating has been analyzed in terms of residual stress and elastic modulus. The coating, deposited on silicon substrate at temperatures higher than $600^{circ}C$, showed itself to be sound, without surface cracks. When the residual stress of the coating was measured using the Stoney formula, it was found to be considerably lower than the value calculated using the elastic modulus and thermal expansion coefficient of bulk $Y_2O_3$. In addition, amorphous $SiO_2$ and crystalline $Al_2O_3$ coatings were similarly prepared and their residual stresses were compared to the calculated values. From nano-indentation measurement, the elastic modulus of the $Y_2O_3$ coating in the direction parallel to the coating surface was found to be lower than that in the normal direction. The lower modulus in the parallel direction was confirmed independently using the load-deflection curves of a micro-cantilever made of $Y_2O_3$ coating and from the average residual stress-temperature curve of the coated sample. The elastic modulus in these experiments was around 33 ~ 35 GPa, which is much lower than that of a sintered bulk sample. Thus, this low elastic modulus, which may come from the columnar feather-like structure of the coating, contributed to decreasing the average residual tensile stress. Finally, in terms of toughness and thermal cycling stability, the implications of the lowered elastic modulus are discussed.
Key words: Yttrium oxide, Residual stress, Elastic modulus, Nano indentation
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