Abstract:Commercial nanosized alumina and titania particles were selected as raw materials to prepare the blended slurry with composition of Al₂O₃-13%TiO₂ (mass fraction), which were reconstituted into micrometer-sized granules by spray drying, subsequently sintering at different temperatures to form nanostructured feedstock for thermal spraying, and then Al₂O₃-13%TiO₂ nanocoatings were deposited by plasma spraying. The evolution of morphology, microstructure, and phase transformation of the agglomerated powder and as-sprayed coatings were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results show that Al₂O₃ retains the same α phase as the raw material during sintering, while TiO₂ changes from anatase to rutile. During plasma spraying, some α-Al₂O₃ phases solidify to form metastable γ-Al₂O₃, and the volume fraction of α-Al₂O₃ decreases as CPSP increases. However, peaks of the TiO₂ phase are not observed from the as-sprayed coatings except for the coatings sprayed at the lower CPSP. As the CPSP increases, nanostructured TiO₂ is dissolved easily in γ-Al₂O₃ or χ-Al₂O₃·TiO₂ phase. After heat treatment, γ-Al₂O₃ in the coatings transforms to α-Al₂O₃, and rutile is precipitated.

Key words: Al₂O₃-13%TiO₂; nanocrystalline powder; nanocoatings; phase evolution