Co,Ni-base alloy thin films deposited by r.f. magnetron sputtering in Ar/N2 atmosphere

Phase composition and microstructure of CoNiCrAlY thin films deposited by r.f. Magnetron Sputtering in reactive Ar/N2 atmosphere were determined by X-ray Diffraction. Three basic phases were observed, for increasing nitrogen partial pressure: (a) a nanocrystalline supersaturated solid solution of the alloy elements with fcc structure and interstitial nitrogen (up to 10–15%), with a sharp [111] fibre texture turning into a broad [200] component for increasing N2 content; (b) an amorphous phase with nominal composition M2N (with M as the alloy elements); and (c) a nanocrystalline nitride approaching the nominal composition MN. Nanocomposite coatings made of nanocrystalline fcc metal phase embedded in an amorphous matrix can be formed in a relatively narrow N2 partial pressure range, whereas at high nitrogen content the thin films tend to form an increasing fraction of a nanocrystalline nitride in addition to the amorphous matrix. Scratch test results are different for the various systems: thin films made of (a) behave as typical plastic metals, with an increased scratch test resistance for increasing N2 content; amorphous (b) films show a very good scratch test behaviour and tend to fail in a plastic mode, with optimal properties for systems made of fcc metal nanocrystalline/amorphous nanocomposites; thin films with a high N2 content tend to behave in a brittle way for increasing content of the nanocrystalline nitride phase.