Annealing Ni nanocrystalline on WC–Co

The effects of annealing temperature on nanocrystalline sputter-deposited Ni thin films (500 nm) deposited on WC–Co (4 wt.%) were investigated. Special attention was focused on quantitative evaluation of residual stress and Ni diffusion into the WC–Co, after heat treatment, from 873 to 1273 K. The estimated level of residual stress, as measured by X-ray diffraction, is around −1.3 ± 0.1 GPa for the as-deposited film, whereas after annealing at 1273 K it decreases significantly. Atomic force microscopy shows that high annealing temperature results into an exponential increase of the roughness. An intermixing between the nanocrystalline Ni and the Co from WC substrate occurs, as it is revealed by quantitative depth-resolved Rutherford backscattering spectrometry analysis and also supported by X-ray photoelectron spectroscopy. We ascribe a significant stress relief with the increasing annealing temperature to the diffusion process. The understanding of this process is particularly important in WC–Co parts with the surface treated with Ni in order to improve the maximum surface service temperature.