Lubricious zinc titanate coatings for high temperature applications

Abstract

Processing–structure–tribological property interrelationships are reported for as-deposited and ex situ annealed atomic layer deposition (ALD) nanocrystalline zinc titanate (ZnxTiyOz) coatings. Annealed coatings at 550°C exhibited improved friction (steady-state friction coefficient of ~0.12) and wear rate (1×10−7mm3/N·m) compared to the as-deposited coatings. The ilmenite structure ZnTiO3 (104) texture, which is present at temperatures up to 550°C, was responsible for improved friction and wear compared to other phases/structures, e.g., Zn2TiO4 cubic spinel structure, annealed at T>550°C. Nanoscale sliding-induced plastic deformation was possible when TEM observed ZnTiO3 (104) stacking faults were sheared parallel to the sliding direction resulting in an intrafilm shear velocity accommodation mode. This subsurface aided in shear accommodation and prevented brittle fracture. Since there is predominately (104) slip, i.e., no interacting slip systems that lead to localized hardening and resistance to shear, this further translated to low friction and wear. Thus, it is feasible to generate high temperature lubricious oxides through nanostructural control of coating growth texture and defects.