The smoothness, hardness and stress in titanium nitride following argon gas cluster ion beam treatment

The surface smoothing of TiN coatings, deposited by CVD or PVD methods, by argon ion clusters comprising a few hundred to a few hundred thousand atoms and carrying a single positive charge has been confirmed. In addition, the present work has shown that there was no change in the mechanical condition, nanohardness or residual stress, of the PVD coatings after treatment. In contrast, the nanohardness in the near-surface region of the CVD TiN coating was increased but, remarkably, there was no concomitant increase in residual stress. A comparison is made with the established effects of classical single ion implantation on the near-surface properties of TiN where a high compressive residual stress is developed if the ion energy lies beyond a threshold value. It was concluded that only a fraction of the atoms in the cluster impact the surface and the vast majority of argon atoms move sideways. It appears to be generic that the smaller clusters are responsible for the increase in hardness as well as the well-known lateral sputtering effects associated with the technology. Larger clusters do not carry enough energy per atom to cause such effects and their energy is dissipated in the substrate as heat.