Combined filtered cathodic arc etching pretreatment–magnetron sputter deposition of highly adherent CrN films

CrN films were prepared on steel substrates by a hybrid method utilizing filtered cathodic arc for Cr ion pretreatment and magnetron sputtering for coating deposition. During pretreatment the substrates were biased to −1200V and exposed to filtered chromium plasma. The substrate-coating interface formed during the pretreatment contained a Cr-enriched modified layer with composition that was strongly influenced by the temperature of the substrate as observed by scanning transmission electron microscopy—energy dispersive spectroscopy. The modified layer had a nanocrystalline morphology and thickness of 15nm. The path of formation of the layer is linked to the combined action of implantation, diffusion, and resputtering. The resulting adhesion of 3μm thick CrN films was very high with scratch test critical load values of 83N. The morphology of the films was smooth without large scale defects and the microstructure was columnar. The coatings behaved well in dry sliding tests with very low wear coefficients of 2.3×10−16m3N−1m−1, which can be linked to the high adhesion and defect-free microstructure. The smooth coatings also had a high resistance to corrosion as demonstrated by potentiodynamic tests with particularly high pitting potentials of +800mV.