Impact wear and abrasion resistance of CrN, AlCrN and AlTiN PVD coatings

The properties of CrN, AlCrN and AlTiN coatings deposited on cemented carbide substrates by a multiple-arc Physical Vapour Deposition (PVD) technique were evaluated by cyclic impact wear and micro-scale abrasion testing. In the impact wear test, a 6 mm diameter tungsten carbide ball was used as the impacting body and the impact frequency (f) was set at 10 Hz. In the micro-scale abrasion test, a micro-blasted 25 mm diameter hardened steel ball was used as the counterface and a suspension of SiC particles (mean size of 4–5 μm) in distilled water as the abrasive slurry. After these wear tests, the wear craters were studied by stylus profilometry, SEM and EDX, to investigate wear behaviour. It is shown that the CrN coating suffered much more severe impact deformation as compared to the two ternary coatings, and exhibited a non-linear increase of the maximum wear depth with increasing number of impact cycles. The impact wear mechanisms of the CrN coating were mainly plastic deformation and micro-delamination. The AlTiN coating exhibited the worst impact wear resistance among the three coatings, mainly due to adhesive wear; in contrast, the AlCrN coating exhibited a lower tendency for the coating to pick-up the ball counterface material, and accordingly demonstrated good impact wear resistance. The AlCrN coating exhibited both the best impact wear performance and the best abrasion resistance amongst the three coatings. The CrN coating exhibited the worst abrasive wear resistance due to its comparatively low hardness. The abrasive wear mechanisms of the CrN coating were a combination of plastic deformation, fine micro-cracking and micro-spallation. The AlTiN coating suffered more severe abrasive wear compared to the AlCrN coating, although both coatings had similar hardnesses.