Influence of ion bombardment on structure and properties of unbalanced magnetron grown CrNx coatings

The structures and properties of reactive unbalanced magnetron sputtered CrNx can be influenced by variation of the substrate bias voltage and substrate bias current density. At floating potential (U-f = -25 V) the lattice parameter coincides with that of the bulk value for CrN and the compressive stress approaches almost 0 GPa. Increasing the negative bias voltage to -200 V results in a steep increase of the lattice parameter together with an observed increase in the intrinsic stress to 1GPa mu m(-1) at U-b = -200 V. In parallel a change in the texture was observed. At bias voltages below U-b = -50 V the (111) orientation is dominating. whereas at higher bias voltages (220) becomes the major texture. Increasing the bias current density leads also to an increase in the lattice parameter and internal stress from zero at a bias current density of 0.9 mA cm(-2) to 1.1 GPa mu m(-1) at a bias current density of 4.4 mA cm (-2), Increasing ion bombardment densifies the coatings as can be observed from the hardness increase of HV2120 at 0.9 mA cm(-2) to HV2440 at 4.4. mA cm (-2) at a bias voltage level of U-b = - 100 V. The ion energy (bias voltage) obviously influences the hardness more than does the ion flux (bias current density): At U-b = 0 V a hardness value of HV1300 was observed in contrast to HV2200 at U-b = -200 V. In parallel the composition declines to lower nitrogen contents with increasing bias voltage levels, but is more or less independent of the bias current density. (C) 1999 Elsevier Science S.A. All rights reserved.