Scratch resistance and wear of CrNx coatings

Hard CrNx coatings of 3.3–4.1 μm in thickness were deposited by means of reactive sputter deposition in an industrial PVD coater. The coatings were deposited under various N2 flows on high-speed steel (HSS) and hot work tool steel (HWTS). For all coatings, the hardness, reduced modulus and density were approximately 30 GPa, 240 GPa and 6400 kg/m3, respectively. The composition, however, varied with the N2 flow from CrN0.6 to CrN1.0.The coatings were subjected to scratch testing with a diamond Rockwell stylus under a progressive load. From the scratch tests, the critical load for the onset of chipping and/or spalling for each coating was determined. The tribological properties of the coatings were characterised by pin-on-disk testing employing an Al2O3 ball as counter part. The wear track depth profile measured with a laser scanning confocal microscope was used to obtain the wear area. From the wear area, the specific wear rate was determined.The CrN1.0 coatings outperform the CrN0.6 coatings with respect to specific wear rate and critical load. For the CrN0.6 coating, similar failure was observed in both the wear test and the scratch tests. The similarity of failure in both tests is discussed.