The Effects of Annealing Treatment on the Nano-Mechanical Properties and Nano-Tribological Behaviors of Nitrogen-Doped Diamond-Like Carbon (DLC) Coatings

Diamond-like carbon (DLC) coatings doped with different nitrogen contents were prepared by an ECWR-CVD deposition technique and vacuum-annealed at different temperatures. The structures, nano-mechanical properties and nano-tribological behaviors of the annealed coatings were characterized using Laser Raman Spectroscopic technique and Hysitron Triboindenter, respectively. The annealing temperature promotes the increase in the sp2 ratio and decreases evidently the nano-mechanical properties, including nano-hardness and reduced modulus. For the as-deposited DLC coatings with different nitrogen contents, the frictional coefficients (L_F /N_F) deduced from nano-scratch testing at same loads are similar, and, therefore, seem to be independent of the added nitrogen content. However, Annealing treatment has a significant effect on the frictional coefficient for the N-doped DLC coatings. In addition, the increasing extent of the frictional coefficient with the annealing temperature for the annealed N-doped DLC coatings varies depending on the nitrogen content in the coatings.