TEM study of the oxidation resistance and diffusion processes in a multilayered TiSiN/TiN(Ag) coating designed for tribological applications

Abstract

This work investigates the structure evolution of a multilayered TiSiN/TiN(Ag) coating with heating, oxide scale growth, diffusion processes occurring during oxidation, and changes in the structure and chemical composition of the non-oxidized zone. The coatings have a multilayered structure with a bilayer periodic thickness of ∼40 nm. The TiN(Ag) layer consists of fcc TiN and Ag crystalline phases, where Ag nanocrystallites are homogenously distributed at the TiN grain boundaries. The TiSiN layer consists of fcc TiSiN solid solution grains and an amorphous a-SiNx phase which segregates at the TiSiN grain boundaries. In-situ hot-XRD analysis shows that the first signs of oxidation occur at 800 °C, when rutile-TiO2 starts to form. The oxidized part of the coating is Ag depleted, except the top layer terminating the structure, which contains some 1–3 nm Ag clusters. Ag diffuses towards the surface from oxidized zones. The cross-sectional analysis also shows no signs of recrystallization and structural changes, except for stress relaxation in the non-oxidized part after annealing at 800 °C. No Ag redistribution or diffusion is found in the non-oxidized part, even close to the interface with the oxide layer, which suggest effectiveness of the multilayered design to mitigate uncontrolled Ag migration towards the surface.