Optimum Design of Ceramic Spray Coating Evaluated in Terms of Intensity of Singular Stress Field

Abstract

Hearth rolls are the most important tools in continuous annealing line to produce thin steel sheet. Usually, the roll surface is coated by ceramics using thermal spraying. However, material mismatch and temperature change may cause thermal stress leading to the failure of the coating and deteriorating high adhesive strength and wears resistance. Therefore, it is very important to improve the debonding strength by optimizing the design of spray coating. The traditional method of evaluating the debonding strength of spray coating is prescribed as JIS H8304 thermal test. This paper focuses on the intensity of singular stress field (ISSF) at the end of interface since few research is available in terms of ISSF. Previously, the authors considered the JIS specimen assuming a plane strain. However, since the hearth roll is cylindrical and axi-symmetric, the difference between plane strain and axi-symmetric models should be clarified. Thus, in this paper, the axi-symmetric model is newly considered and the optimum design is discussed by varying the coating material and the coating thickness. Also the present results are compared with the previous results of JIS specimen so that the difference between actual model and JIS specimen can be clarified to contribute the design and evaluation of the real rolls.