Mechanical properties and oxidation resistance of nanocomposite TiN–SiNx physical-vapor-deposited thin films

Abstract

Abstract Thin films of TiN–SiN x have been prepared by reactive unbalanced magnetron sputtering from two opposite Ti and Si targets. The silicon concentration in the deposited coatings is varied between 0 and 16 at.%. The deposited films are composed of TiN nanocrystallites embedded in an amorphous SiN x matrix. These nanocomposite coatings exhibit improved mechanical properties in comparison with TiN deposited under the same conditions. Whereas the hardness measured by nanoindentation is about 27 GPa for TiN, it reaches 38 GPa in TiN–SiN x films containing 5 at.% Si and decreases to the values of amorphous SiN x at silicon concentrations above 15 at.%. Besides higher hardness values and improved wear resistance, these composite coatings are superior to TiN in their resistance against oxidation. The oxidation resistance is gradually enhanced by increasing the silicon concentration in the films. At 800°C in air, TiN–SiN x films with an Si content as low as 5 at.% exhibit a one order of magnitude lower oxidation rate compared with that of TiN. This oxidation resistance improvement is explained by the presence of the amorphous SiN x phase at the TiN grain boundaries, which limits the oxidation in these high diffusion paths and prevents recrystallization of TiO 2 .