M. Arai, Central Research Institute of Electric Power Industry, Tokyo, AL, Japan; E. Wada, K. Kishimoto, Tokyo Institute of Technology, Tokyo, Japan; N. Ohno, Plasma Giken Co. Ltd., Toda City, Saitama, Japan
It is known that thermal spray condition affects on coating properties such as elastic modulus, coefficient of thermal expansion, coating fracture strength and coating cohesive strength. Therefore, residual stress formed in thermal barrier coating and coating stress generated during in-service is dramatically changed with the thermal spray condition. In this study, we examined about effect of several kinds of thermal spray conditions on those properties of the coating. Typical thermal barrier coating system composed of zirconia top coating (its chemical composition is 8wt%Y2O3-ZrO2) and CoNiCrAlY bond coating was selected here. Thermal spray condition was changed with flight particle velocity, flight particle temperature and pre-heated substrate temperature. Elastic modulus, coefficient of thermal expansion (CTE), Vickers hardness, fracture toughness of splat boundary, pore fraction and then coating residual stress as the coating properties were examined systematically. As obtained results from those measurements, it was found that each spray condition did not affect on elastic modulus and CTE of ceramic coating. However, fracture toughness of splat boundary and Vickers hardness were larger changed with particle velocity and were not also changed with pre-heated substrate temperature. Residual stress in the coating was estimated by considering those coating properties obtained in this study and the shear-lag model proposed by us for representing thermal spraying process.
Summary: It is known that thermal spray condition affects on coating properties such as elastic modulus, coefficient of thermal expansion, coating fracture strength and coating cohesive strength. Therefore, residual stress formed in thermal barrier coating and coating stress generated during in-service is dramatically changed with the thermal spray condition. In this study, we examined about effect of several kinds of thermal spray conditions on those properties of the coating. Typical thermal barrier coating system composed of zirconia top coating (its chemical composition is 8wt%Y2O3-ZrO2) and CoNiCrAlY bond coating was selected here. Thermal spray condition was changed with flight particle velocity, flight particle temperature and pre-heated substrate temperature. Elastic modulus, coefficient of thermal expansion (CTE), Vickers hardness, fracture toughness of splat boundary, pore fraction and then coating residual stress as the coating properties were examined systematically. As obtained results from those measurements, it was found that each spray condition did not affect on elastic modulus and CTE of ceramic coating. However, fracture toughness of splat boundary and Vickers hardness were larger changed with particle velocity and were not also changed with pre-heated substrate temperature. Residual stress in the coating was estimated by considering those coating properties obtained in this study and the shear-lag model proposed by us for representing thermal spraying process.
