Recent progress in the study of physically vapour-deposited coatings produced by means of highly ionized plasmas

Abstract

To the existing data on the effects of substrate temperature, bias voltage, substrate current density, and deposition rate on the microstructure of hard physically vapour-deposited coatings, this paper adds new results on these phenomena, obtained by means of X-ray diffraction in Field-Merchant reflection mode for physically vapour-deposited TiN on AISI 304 and AISI H13 substrates. It could be shown that there is a combined effect on the preferential orientation of the coating of the nature of the substrate surface (metallurgical composition and preferential orientation) on the one hand and of the energy deposition per condensing atom on the other hand. Although the substrate surfaces of both materials are preferential orientation free, the coating starts to grow on AISI H13 without any preferential orientation independent of the applied voltage V= V b- V p ( V b is the bias voltage, and V p the plasma potential) in the range [−60 V, −160 V], as could be expected, whereas on AISI 304 a (200) orientation develops. At larger thickness (about 1.5 μm) a (220)−(111) texture is observed for both substrate materials with a mosaic spread of about 8−10° for both orientations, except for the − 60 V case for AISI H13, where a mosaic spread of about 34° is observed for the (111) orientation, and for the − 60 V case for AISI 304 where the initial (200) texture has survived with a small increase in mosaic spread to about 9°. Data on the internal macroscopic residual stresses for TiN on AISI H13 show that they are compressive and that they decrease with decreasing energy deposition. Because in this case a larger mosaic spread of the preferential orientation is observed at lower energy depositions, this indicates the effect that mosaic spread may have on internal stresses. It is also observed, on samples of ASP 23, that properties such as hardness and conformai cracking in a scratch test are changing with the amount of compressive stress in such a way that real functional properties, such as wear resistance, might deteriorate with decreasing compressive stress. Finally, the analysis of ( d hki , sin 2 ψ)curves, which is made in order to determine the amount of stress in the coating, has shown that the observed ψ +− ψ −splitting can, in the present case, largely be explained on the basis of the observed preferential orientation.