An Evaluation of the Adhesive Strength of the Interface between a Coating and Substrate

Abstract

Scratch tests were carried out on TiC and TiN coatings which had been deposited by PVD (Physical Vapor Deposition) and CVD (Chemical Vapor Deposition) techniques. The critical load L c was detected by the acoustic emission method (AE) and also by the frictional force curve. The critical load corresponded to the load at which local delamination of coating was observed on the scratch track. A study the scratch tracks induced in a coating during the scratch test revealed that fine cracks, which propagated parallel to the scratch track, were created before local delamination occurred. Other cracks, which propagated perpendicular to the scratch direction, were observed to form in the scratch track at the critical load. Localized delamination also occurred at the edge of scratch track at L c . The stress distribution at the interface was estimated by FEM (Finite Element Method) analysis. From both the experimental and analytical results, it was found that local delamination occurred at a critical shear stress at the interface between coating and substrate. Since the shear stress at the interface decreased with decreasing tangential force, the critical load L c increased with decreasing of tangential force. Indentation tests without tangential force was also carried out. The critical load was higher in the indentation test compared to that in scratch test. However, the critical shear stresses at the interface for both scratch and indentation tests coincided with each other. It was concluded that the adhesive strength between coating and substrate is a function of the critical interfacial shear stress.