Superhard nanocomposite Ti-Si-N coatings

r.f. reactive magnetron sputtering technique was used to deposit Ti-Si-N films with Si contents in the range 0-20 at. %. X-ray diffraction (XRD) patterns and Transmission Electron Microscopy (TEM) analyses revealed the nanocrystalline nature of these coatings. XRD patterns of sputtered films revealed the presence of 2 crystalline phases, where phase I (lattice parameter of about 0.429 nm) can be assigned to a cubic Bl NaCl structure, typical for TiN, and phase 2 is also a fee type structure, but with a smaller lattice parameter (similar to 0.418 nm). The mixture of the two phases in some samples indicates that, in general, the segregation of TiN and SiNx phases is not complete, leading to a possible mixture of TiN grains and regions constituted by a so-called solid solution. Optimum hardness values were found for Si contents in the range 6-13 at. %, with a maximum of 54 GPa being recorded. However these results are very much dependent on deposition conditions, where the main factors are the substrate temperature and the ion bombardment during deposition. The correlation between mechanical and structural properties is outlined in this paper.