Abstract
CrCuAgN PVD nanocomposite coatings were produced using pulsed DC unbalanced magnetron sputtering. This investigation focuses on the effects of post-coat annealing on the surface morphology, phase composition and nanostructure of such coatings. In coatings with nitrogen contents up to 16 at.%, chromium exists as metallic Cr with N in supersaturated solid solution, even after 300 oC and 500 oC post-coat annealing. Annealing at 300 oC did not obviously change the phase composition of both nitrogen-free and nitrogen-containing coatings; however, 500 oC annealing resulted in significant transformation of the nitrogen-containing coatings. The formation of Ag aggregates relates to the (Cu+Ag)/Cr atomic ratio (threshold around 0.2), whereas the formation of Cu aggregates relates to the (Cu+Ag+N)/Cr atomic ratio (threshold around 0.5). The primary annealing-induced changes were reduced solubility of Cu, Ag and N in Cr, and the composition altering from a mixed ultra-fine nanocrystalline and partly amorphous phase constitution to a coarser, but still largely nanocrystalline structure. It was also found that, with sufficient Cu content (> 12 at.%), annealing at a moderately high temperature (e.g. 500 oC) leads to transportation of both Cu and Ag (even at relatively low concentrations of Ag, ≤ 3 at.%) from inside the coating to the coating surface, which resulted in significant reductions in friction coefficient, by over 50% compared to that of the substrate (from 0.31 to 0.14 with a hemispherical diamond indenter, and from 0.83 to 0.40 with an alumina ball counterface, respectively). Results indicate that the addition of both Cu and Ag (in appropriate concentrations) to nitrogen-containing chromium is a viable strategy for the development of ‘self-replenishing’ silver-containing thin film architectures for temperature-dependent solid lubrication requirements or antimicrobial coating applications.
Original language | English |
---|---|
Pages (from-to) | 732-746 |
Number of pages | 15 |
Journal | Applied Surface Science |
Volume | 392 |
Early online date | 13 Sept 2016 |
DOIs | |
Publication status | Published - 15 Jan 2017 |
Keywords
- Nanocomposite; PVD coatings; Annealing; Transportation; Phase transformation; Nanostructure