Characterisation of chromium nitride films prepared by ion-beam-assisted deposition

Chromium nitride films are a promising alternative to both electroplated hard chromium and TiN coatings prepared by physical vapour deposition (PVD). Deposition of the former still mostly requires highly toxic Cr(VI) solutions, causing environmental problems. Titanium nitride is an excellent hard coating but cannot efficiently protect the substrate from corrosion. Recently, some groups have obtained interesting results about PVD CrxN deposited by magnetron sputtering. In this work CrxN deposition was realised by ion-beam-assisted deposition (IBAD), evaporating chromium under irradiation with nitrogen ions. The arrival ratio of nitrogen ions to chromium atoms (I/A) was kept constant at 0.5, as this was known to be the best region for chromium nitride synthesis. However, the IBAD process allows many other deposition parameters to be varied and detailed investigations of IBAD CrxN are rare. In this study, the influence of ion energy and ion angle of incidence on film formation and properties was investigated. CrxN-coated steel samples were analysed by atomic force microscopy to gather information about morphology changes. In addition, they were investigated with respect to mechanical and corrosion behaviour. The results are discussed in terms of the effect of the ion-induced microscopic changes on the macroscopic properties. It was found that higher ion energy as well as higher ion incidence angle resulted in distinct improvements in corrosion behaviour. Better corrosion behaviour is combined with lower hardness improvements. (C) 1999 Elsevier Science S.A. All rights reserved.