Rayleigh velocities for the evaluation of coating hardness

The Rayleigh or surface wave velocity in a metallic coating electro-deposited on steel was measured and an experimental correlation was found between the velocity and the hardness of the coating. Since qualitative coating properties are commonly inferred from hardness tests, this result suggests the utilization of nondestructive surface ultrasonic velocity measurements to evaluate the coating hardness over regions which are inaccessible to conventional hardness tests, or where it is not possible to allow a hardness indentation. Here we propose a nondestructive ultrasonic technique to evaluate the hardness of electrodeposited chromium coatings, based on the empirical relationship we have relating hardness and Rayleigh velocity. In view of available experimental evidence of relationship between surface hardness and Rayleigh velocity in other bulk metals this relationship should be investigated in other coatings as well