Characterisation of chromium nitride films produced by PVD techniques

Abstract

Chromium nitride thin films have been deposited on stainless steel substrates by r.f. reactive magnetron sputtering. The influence of process parameters such as substrate bias and partial pressure of reactive gas have been investigated. The characterisation of the coatings was performed by X-ray diffraction (XRD), Raman Spectroscopy (RS) and nano-indentation experiments. These studies allow to analyse the influence of deposition parameters in crystal phases, crystal orientationytexture and crystallite size. The relationship between structural defects and their characteristics with deposition conditions will also be taken into account. The presence of oxygen on the coatings surface, due to atmospheric contamination, is analysed by means of Raman spectroscopy. This optical technique can be used for the characterisation of the surface oxides at different stages of oxidation. The changes observed in Raman spectra can be correlated with process parameters. Coatings produced with an unbiased substrate showed higher tendency to surface oxidation. Increasing the nitrogen partial pressure in the working atmosphere produces changes from a hexagonal Cr N to cubic CrN microstructure. The strain in CrN crystals increases with nitrogen content in 2 working atmosphere. When the Cr N phase is dominant the hardness has a relative maximum (42.2 GPa), but the highest hardness 2 was obtained for a coating with dominant CrN phase produced with highest nitrogen flow (44.9 GPa).