A formation mechanism for the macroparticles in are ion-plated TiN films

Characterization of macroparticles in TiN films prepared by an are ion-plating method on AISI 304 stainless steel was carried out by energy filtering transmission electron microscopy. The results show that most of the macroparticles have the shape of a bud, which has the equiaxial polycrystalline Ti metal located at the bottom center. The outerlayer consists of TiN0.26, alpha -TiN0.3 and Ti2N, in addition to TiN, identified by selected area diffraction. On the basis of the analysis, a model describing the formation of macroparticles in the are ion-plated TiN is proposed. Once emitted from the cathode, the liquid Ti droplets react with nitrogen during their migration to the substrate and form a thin layer of titanium nitrides on the surface of the droplets, resulting in a core-shell structure. As a result of the high-melting outshell, flattened torus voids are produced, upon impact on the substrate, beneath each particle which causes shadowing of the ion flux during deposition. Subsequent growth of TiN follows the orientation of the titanium nitride nuclei in the outshell to form a radial type structure, until coalescence with the regular TiN columns grown perpendicular to the substrate surface occurs. (C) 2001 Elsevier Science B.V. All rights reserved.