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

Abstract

Cr–N coatings were grown by arc 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 β-Cr 2 N 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 arc-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.