Evaluating Residual Stress And Interfacial Bonding Strength Of Ceramic Coatings By Relative Method

With the rapid development of science and technology,the working conditions of equipments and components are increasing demanding,consequently traditional material cannot fulfill the needs.Ceramic coatings have developed rapidly due to its excellent resistance of high temperature,corrosion and oxidation.For ceramic coatings,accurate evaluation of residual stress and interficial bonding stress is the premise of safety and reliability of the structure and vital to the process and service.However,the evaluation method of residual stress and interficial bonding stress exist mant defects.For residual stress,ceramic coatings are diveded into two kinds according to the preparation temperature of coating and substrate: the isothermal coatings which is at same preparation temperature,for instance the CVD coating,and the heterothermal coatings which is at different preparation temperature,for instance the thermal spraying coating.On the other hand,the interficial bonding stress of coating has evaluated by improving the cross-donded method,while the interface failure mode has analysised by relative method.1.For the evaluation of residual stress in isothermal ceramic coatings,residual stress evaluation equation is established based on the uniform strain model,using the relative method,by measuring elasticity modulus,thermal expansion coefficient,cross-sectional area of coating and substrate.2.For the evaluation of residual stress in the hetero-thermal ceramic coating,the single-sided coatings with measurable bending deformation,which can be analysised by Stoney method,are defined as Stoney coating,while others are defined as un-Stoney coating,while the coating components in engineering practice are almost un-Stoney coating.In this study,the analytic relation of residual stress between Stoney coating and un-Stoney coating is established by relative method,thus,the residual stress in un-Stoney coating can be caculated using the residual stress in Stoney coating which can be evualuated by Stoney method.3.For the bond strength of ceramic coating,in the improved cross-bonded shear test,interface is subjected to a single shear force,while test is no longer limited to the strength of adhesives;the improved cross-bonded method has avoid the effect of the friction between the fixture and sample in tensile bond strength test,improving the accuracy of results.