Evaluation of adhesion and properties of sprayed coating by ultrasonic testing method

It is well known that the adhesion of thermal sprayed coating is relatively low and it tends to delaminate from substrate during practical use. Therefore, some testing methods to evaluate the adhesion of coating are proposed and used practically. However, these methods used destructive method and can not be applied for products. Recently some of the authors have proposed a non-destructive method using ultrasonic wave and shown the effectiveness of the method on the evaluation of the adhesion of coating. However, the method is very simple and the measurement is not always precise. On the other hand, the porosity in the coating affects the properties of the coating and some methods to evaluate porosity are proposed. However, every method is not simple and sometimes special equipments are necessary. Therefore simple and precise method has been required In this study, a new method to evaluate simultaneously the adhesion and properties of thermal sprayed coating is proposed The method uses ultrasonic testing method and the properties are surmised by the impedance of coating detected by ultrasonic surface echo method In this case, since the bottom echo is affected by impedance of the coating, in the calculation of transmittance coefficient the impedance is taken into consideration and adhesion is surmised by the transmission coefficient. As the result of the experimental investigation, it is confirmed that the method proposed is effective to the evaluation of adhesion and properties of sprayed coating.