Thermal stability of Cr_(1-x)Al_xSi_yN coatings with medium to high aluminium content prepared by arc evaporation

摘要

The thermal stability of Cr_(1-x)Al_xN and Cr_(1-x)Al_xSi_yN nanocomposite coatings with different composition x, Si content, and phase structure has been investigated. The coatings were deposited in an industrial unit by the cathodic arc evaporation method, using rotating cylindrical cathodes. Further sets of coated WC/Co plates were subjected to an annealing step in a forming gas (92% N_2 / 8% H_2) atmosphere for several hours at a constant temperature (maximum 1000°C). Chemical composition, microstructure and mechanical properties of the coatings were investigated by the RBS, XRD, TEM, SEM, XPS and nanoindentation techniques. As-deposited Cr_(1-x)Al_xSi_yN coatings with Al contents x in the range of 0.4 ≤ x ≤ 0.6 showed a single-phase cubic CrAlN structure and a maximum hardness of 38 GPa. With increasing the Al content to x = 0.95 - 0.96, two-phase films consisting of hexagonal AlN and cubic CrAlN structure with hardness of about 31 GPa were obtained. The hardness of Cr_(1-x)Al_xSi_yN coatings increases during annealing at temperatures in the range of 800 - 1000°C by about 1 - 4 GPa, even though the residual compressive stress in the coatings was found to relax considerably during this procedure. The addition of Si into Cr_(1-x)Al_xN delays the appearance of hcp-AlN and thereby improves the thermal stability of the coatings.