Assessment of adhesion of Ti(Y)N and Ti(La)N coatings by an in situ SEM constant-rate tensile test

A so-called constant-rate tensile test technique is proposed to assess the adhesion performance of ion-plated hard coatings to the substrate, in which the coated sample is elongated at a constant-rate in a scanning electron microscope, while the changes in the coating surface are observed and recorded. Critical elongation of the sample, which corresponds to the start of detachment of the coating from the substrate, has proved to be suitable for adhesion assessment. A comparative study shows that the proposed technique gives the same ranking for a number of coating/substrate systems as the classical scratch test does. It is shown that enhancement of the adhesion performance for the TiN coatings can be achieved by adding rare-earth elements such as Y and La and by introducing nitriding sublayers to the system. These beneficial effects are discussed in terms of the alteration of the microstructure of the transition zones in the systems.