Hardness and scratch response of PVD multilayer coatings

Abstract

In the present investigation, novel Cr/CrN, CrN/CrAlN and Cr/CrN/CrAlN multilayered coatings thin films have been developed by dual RF magnetron sputtering. They consist of superposing Cr, CrN and CrAlN layers of 50–500nm thick, up to a total thickness of 0.45–1μm. These coatings were grown on AISI4140 steel samples. The mechanical properties of these coatings were studied by scratch-tests and nano-indentation measurements. The hardness of the films reaches 15.8 GPa for a Cr/CrN multilayered coating sputtered at a bias voltage of -900V. High peak load tests were used to estimate the film adhesion on steel substrates; critical loads (Lc2) of 11N showed weak adhesion properties of the film. Moreover, an inventory of the major scratch-tests failure modes was established, which were classified into plastic deformation and different forms of cracking, spallation and coating perforation events. No evidence of interfacial failure(s) of the sub-layers was observed after the adhesion and nanoindentation tests.