Investigation of adhesion of PVD coatings using various approaches

Three different coatings (TiN, CrN and AlCrN layers) were deposited on an AISI 52000 steel substrate with the physical vapour deposition technique. Adhesion of the coatings was investigated by microindentation, scratch testing and cyclic impact testing. In the microindentation tests, circumferential cracks were observed around the indentations on each coating. The scratch tests revealed the critical forces that accompanied the various types of degradation imposed by scratching. The TiN coating demonstrated the lowest critical force of adhesion, whereas the CrN coating had the highest and AlCrN had an intermediate critical force of adhesion. According to the results from impact testing, all coatings displayed circumferential and radial cracks that degenerated in varying manners during the cycles. Indeed, the cyclic impact introduced crazing on the TiN coating as a broad halo around the imprint, while for AlCrN, an intensive delamination was observed. The CrN coating was found to crack, but did not delaminate.