Optimization of Alumina Slurry Properties and Drying Conditions in the Spray Drying Process and Characterization of Corresponding Coating Fabricated by Atmospheric Plasma Spray

Abstract

In this paper, alumina (Al2O3) slurry properties and spraying drying conditions were optimized by orthogonal experiment for preparing the dense and spherical alumina feedstock. The feedstock was carried in a moving gas stream and deposited on the stainless substrate by atmospheric plasma spray (APS).The phase composition and microstructure of feedstock and as-sprayed coatings were studied by XRD, SEM and TEM. In addition, the porosity, surface roughness and micro hardness of as-sprayed coatings were also investigated. The results showed that Al2O3 powder content in slurry was the most influential factor for the particle size and morphology of feedstock and most of α-Al2O3 existing in the starting feedstock transformed into γ-Al2O3 during APS. Moreover, it was found that, using the feedstock prepared by optimized parameters, the as-sprayed coating had an average grain size of about 250 nm, with lower porosity of about 4 %, surface roughness Ra of about 1.94 μm, micro hardness HV0.3 of about 1000 under applied load 300 g.