Fatigue and mechanical properties of nanostructured and conventional titania (TiO2) thermal spray coatings

Nanostructured and conventional titania (TiO2) coatings were thermally sprayed using air plasma spray (APS) and high velocity oxy-fuel (HVOF) processes. The fatigue and mechanical properties of these coatings were investigated. A previous study characterized these coatings by scanning electron microscopy (SEM) to investigate the microstructural features and Vickers indentation to determine the hardness and crack propagation resistance. This current complementary SEM work examined fracture surfaces of fatigue-tested samples to assess crack nucleation and to study mechanisms of deformations. The fatigue strength of coatings deposited onto low-carbon steel (AISI 1018) showed that the nanostructured titania coated specimens exhibited significantly higher fatigue strength compared to the conventionally sprayed titania. The strain–time curve of AISI 1018 coated with TiO2 indicated that the strain amplitude of the HVOF-sprayed nanostructured TiO2 coating was much lower than the corresponding data of APS conventional TiO2. SEM analysis of fracture surfaces revealed valuable information regarding the influence of these coatings on the performance of the coated component. This investigation gives new understanding to the nature of fatigue and deformation of the nanostructured and conventional titania (TiO2) coatings.