The effects of bias voltage and annealing on the microstructure and residual stress of arc-evaporated Cr-N coatings

Cr-N coatings were grown by are evaporation on high-speed steel substrates. Coatings were grown by using a nitrogen partial pressure of 8 Pa and different negative substrate bias voltages, V-S, ranging between 20 and 400 V. The coatings consisted of cubic CrN and chromium phases for all biases except at 400 V, where the hexagonal beta-Cr2N phase was also detected. The overall coating composition was substoichiometric, with N/Cr equal to 0.8+/-0.08 for all coatings. The residual stress in the coatings was always compressive and showed a bias dependence similar to that reported for other are-evaporated coatings of transition metal nitrides. The thermal stability of these coatings was examined by annealing samples grown at V-S=50 and 300 V, which had the same level of initial residual stress. The residual stress was found to be thermally stable up to the (bias-dependent) deposition temperatures, but to decrease rather rapidly at higher temperatures. These results are discussed, together with the bias-dependent stress observations, in terms of defect diffusion together with defect generation and annihilation in the collision cascade. (C) 1999 Elsevier Science S.A. All rights reserved.