Microstructure and properties of Al2O3-3wt% TiO2 plasma sprayed coating affected by powder manufacturing methods
Conference poster, 2011
Plasma sprayed Al2O3-TiO2 ceramic coatings are widely used as protective coatings for promoting component performance with respect to wear, corrosion, and thermal insulation. In addition, Al2O3-TiO2 is an interesting matrix material for thermally sprayed composite coatings owing to its excellent chemical stability and thermal properties. With regard to dispersion of additives, the improvement of the microstructure homogeneity of conventional thermally sprayed coatings becomes an important aspect of the materials design and manufacturing process. The current study is aiming at controlling the microstructure of plasma sprayed Al2O3-3 wt%TiO2 coatings in terms of developing the feedstock powder manufacturing method. Two Al2O3+3wt% TiO2 powders produced by freeze granulation and different thermal treatment processes were plasma sprayed. The resulting coatings were investigated on microstructure, porosity, phase content, microhardness and crack growth resistance. The phase transformations occurring during thermal spraying are different to the one observed in commercial Al2O3-3 wt%TiO2 powder manufactured with a cladding process. In contrast to the conventional lamellar structure, a high degree of mixing of Al2O3 and TiO2 in the granulated powders results in a more uniform microstructure. Compared with the coating made from the commercial Al2O3-3 wt%TiO2 powder, the improved microstructure leads to a substantial increase of the crack growth resistance parallel to the coating plane without critically deteriorating microhardness of the coatings.