Residual stress development in UMS TiN coatings

TiN coatings produced by the unbalanced magnetron sputtering (UMS) technique were used to study the relationship between the most relevant deposition parameters, such as substrate bias and working gas pressure, and the residual stress level. The coatings were deposited on 300 μm thick silicon and steel substrates to allow residual stress measurements using the surface curvature method. In addition to residual stress magnitude, the UMS TiN coatings were also evaluated for microstructure and hardness. It was found that the properties of TiN coatings could be linked to residual stress magnitude, which was also strongly affected by the deposition conditions and substrate properties. Significantly higher stresses were observed for coatings deposited on steel substrates. The role of intrinsic and thermal stresses in the coating–substrate system was evaluated. In the experimental program, coatings were subjected to thermal cycles exceeding the maximum deposition temperature to produce stress–temperature correlation plots. These relationships were used to evaluate the possibility of post-deposition annealing to relax the residual stress. The correlations between residual stress, coating hardness, and deposition conditions are discussed in this paper.