Microstructure and mechanical properties of plasma sprayed nanostructured TiO2–Al composite coatings

TiO2 and TiO2–Al composite coatings were prepared by plasma spraying using a reconstituted nanosized feedstock via a spray drying method. Effects of various spray conditions on the microstructure, porosity, microhardness and wear resistance related to the mechanical performance of coatings were evaluated. The coatings sprayed using relatively low plasma power were composed of two distinct microstructures of well defined lamellar structure, similar to microstructure of conventional plasma sprayed coatings generated by fully melted particles, and embedded nano or sub-micron particles generated by partial/non-molten particles of feedstock materials. The fraction of partial/non-molten particles in coating layers was increased by Al additive. Such a characteristic of blended microstructure of coatings was clearly confirmed from a bimodal distribution of microhardness described by Weibull plots. The optimized addition of Al into TiO2 increased the spraying efficiency, and also, improved mechanical properties such as microhardness and wear resistance.