Comparison of coating failure induced by indentation and bending test

When applying a coating on to a substrate for any use, a fundamental consideration is its mechanical stability. Generally this is assessed by a scratch test, but owing to the complex stress field involved and the numerous parameters acting on the acoustic emission, with this test even intersample comparison is unreliable. Silicon–carbon films, applied by CVD on to a steel substrate in a microwave device, were tested by Vickers and Rockwell indentation and a three point bending test to initiate damage. The damage induced is described and discussed and the qualitative results are compared. It is shown that features related to the strength and adhesion of the deposit can be deduced from knowledge of the values of the external forces applied in the tests.