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In this work, five different concentrations of a mixture of TiO 2 /Al 2 O 3 nanopowders in an alcoholic suspension at 10wt.% solid content were sprayed by Suspension Plasma Spraying on steel discs. The influence of the presence of TiO 2 at 0, 13, 40 and 75wt.% in Al 2 O 3 was analysed by studying the properties of the sprayed coatings. Microscopy analysis of the projected coatings revealed a homogeneously distributed microstructure, where the densification of the coating increases with TiO 2 content, while the original nanostructure is maintained. A nanoindentation study revealed an increment of nanohardness and elastic modulus due to the densifying effect of TiO 2 . The addition of significant amounts of TiO 2 has been revealed as necessary in order to favour the fusion of Al 2 O 3 in the SPS process. [ABSTRACT FROM AUTHOR]

Al2O3-13%TiO2 coatings were deposited on stainless steel substrates from conventional and nanostructured powders using atmospheric plasma spraying (APS). A complete characterization of the feedstock confirmed its nanostructured nature. Coating microstructures and phase compositions were characterized using SEM, TEM, and XRD techniques. The microstructure comprised two clearly differentiated regions. One region, completely fused, consisted mainly of nanometer-sized grains of γ-Al2O3 with dissolved Ti+4. The other region, partly fused, retained the microstructure of the starting powder and was principally made up of submicrometer-sized grains of α-Al2O3, as confirmed by TEM. Coating microhardness as well as tribological behavior were determined. Vickers microhardness values of conventional coatings were in average slightly lower than the values for nanostructured coating. The wear resistance of conventional coatings was shown to be lower than that of nanostructured coatings as a consequence of Ti segregation. A correlation between the final properties, the coating microstructure, and the feedstock characteristics is given. [ABSTRACT FROM AUTHOR]

Abstract: Al2O3–TiO2 coatings were deposited on austenitic stainless steel coupons from nanostructured powders by atmospheric plasma spraying (APS). Commercial suspensions of nanosized Al2O3 and TiO2 particles were used as starting materials. Mixtures of these suspensions and of more concentrated suspensions of Al2O3 and TiO2 were then agglomerated into plasma sprayable feedstock. Agglomeration was performed by spray drying, followed by consolidation thermal treatment. These powders were successfully deposited, yielding coatings that were well bonded to the substrates. The coating microstructure thus consisted of semi-molten feedstock agglomerates surrounded by fully molten particles that acted as binders. Agglomerates from suspensions with higher solids contents yielded coatings with lower porosity and fewer semi-molten areas. [ABSTRACT FROM AUTHOR]