Synthesis of AlaCraOaN thin films in corundum and f.c.c. structure by reactive r.f. magnetron sputtering

Advanced PVD coatings for metal cutting applications must exhibit a multifunctional property profile including high hardness, chemical inertness and high temperature stability. Recently, ternary AlaCraO thin films with mechanical properties similar or superior to conventional aluminium oxide thin films have been suggested as potential materials meeting such demands. These coatings can be deposited at moderate temperatures in PVD processes. In this work, new quaternary AlaCraOaN coatings are suggested as alternative for offering thin film materials of high strength, hardness and even toughness. A combinatorial approach to the synthesis of AlaCraOaN thin films by means of reactive r.f. magnetron sputtering is presented. A thorough phase analysis of deposited coatings covering a wide range of elemental compositions revealed a well-defined phase transition from a corundum-type I--(Al1ax,Crx)2+I'(O1ay,Ny)3 structure to a CrN-type f.c.c.-(Al1ax,Crx)1+I,(O1ay,Ny) structure as a function of the Al/Cr ratio and the nitrogen gas flow ratio. Detailed results on the coatings composition, constitution and microstructure are discussed compared to ternary AlaCraO thin films deposited by reactive r.f. magnetron sputtering under nearly identical conditions.