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Al2O3+13wt%TiO2 (AT13) particles were doped with 5%～30% nanoparticles and prefabricating powders were prepared by renewed granulation. AT13 coatings were prepared on the surface of steel 45# by air plasma spraying technique with the prefabricating powders. The microstructures of the AT13 prefabricating powders and the resulting coatings were investigated by SEM and EDS and XRD. The samples were undergone corrosion in the medium of 10% H2SO4 aqueous solution at temperature 80℃. The results indicate that the blistering time of coatings in the corrosive medium was increased with the increase of doped nanoparticle concentration while the time from blistering to spalling is independent of nanoparticle concentration. The results revealed that the structure of prefabricating powders was a twisted micrometer grade particle with dimension of 40-60μm, encapsulated by nanoparticles. The homogeneity of element distribution in coatings was improved and porosity was reduced. The phases of (Al2O3) 5.333 and orthorhombic Al2TiO5 were identified . The fracture analysis confirmed that there is a large amount of vermiculate whiskers with diameter of 10nm and length of 100～200 nm in coatings and the fracture type of coatings was the ductile trans-granular fracture.