Influence of composite powders’ microstructure on the microstructure and properties of Al2O3–TiO2 coatings fabricated by plasma spraying

Abstract

Three kinds of alumina–titania composite powders with different microstructure were plasma sprayed to prepare alumina–titania coatings. The influence of composite powders’ microstructure on the microstructure and properties of alumina–titania coatings was investigated. There was typical lamellar structure and columnar grains formed in the conventional micro-composite coating, which were derived from the coarse-grained microstructure and segregated composition of the micro-composite powder feedstock. Comparing with the micro-composite coating, there was not typical lamellar structure and columnar grains in the coatings prepared from nanocomposite powders, which was mainly attributed to the fine-grained microstructure and homogeneous distribution of chemical composition in the nanocomposite powders. There were two types of microstructures formed in the two coatings prepared from nanocomposite powders. Fully-melted regions with splat structure consisting of γ-Al2O3 dissolved with titania and amorphous phase in two nanocomposite coatings were formed by the fully melted nanocomposite powders during plasma spraying. Partially-melted regions with particulate structure consisting of α-Al2O3 and amorphous phase in the nanocomposite coating was formed by the partially melted or unmelted nanocomposite powder with particulate structure, and partially-melted regions with three-dimensional network structure consisting of amorphous intergranular network thin film rich in Ti, Zr and Ce surrounding the α-Al2O3 colonies in the nanocomposite coating were formed by the partially melted or unmelted nanocomposite powder with three-dimensional network structure. The microhardness, crack growth resistance and sliding wear resistance of the coatings prepared from the nanocomposite powders, especially the nanocomposite coating prepared from the nanocomposite powder with three-dimensional network structure, were enhanced comparing with that of the conventional micro-composite coating. The superior properties of the nanocomposite coatings were attributed to the uniform composition distribution in their nanocomposite powders.