Substrate-induced changes of TiN and (Ti, Al)N coatings due to plasma nitriding

Abstract

Some properties of TiN and (Ti, Al)N coatings deposited on plasma-nitrided samples made of steel grades AISI M2 and AISI H11 were analyzed. In all composite plasma-nitrided/hard-coating layer structures the coating-to-substrate adhesion was enhanced compared with the adhesion of the coatings deposited on non-nitrided specimens. The mechanism of a coating failure during the scratch test is influenced by plasma nitriding of the substrate prior to coating deposition, and the compressive stresses in both TiN and (Ti, Al)N coatings are increased. Substrate-induced preferred orientation growth of both coatings is also influenced by the plasma nitriding, but (111) preferred orientation was found in all cases. All coating structures are found to be columnar and very dense, the coating density being increased due to plasma nitriding of steel substrates. An increase of the coating surface roughness is also due to plasma nitriding of the substrates.