Formation of nanocrystalline FeAl 2 O 4 matrix coating by plasma spraying

Abstract

Al–Fe₂O₃ composite powders were deposited onto steel substrate by plasma spraying. The state (temperature and velocity) of the Al–Fe₂O₃ composite powders in plasma flame and the formation mechanism of the nanostructured coating were investigated and analysed. The maximum temperature and velocity of the composite particles in plasma flame were 3274·5°C and 179 m s⁻¹ respectively. FeAl₂O₄, Fe and Al₂O₃ multiphase composite coatings were formed, which presented a microstructure with a number of spherical Fe and Al₂O₃ nanosized grains embedded within the equiaxed and columnar FeAl₂O₄ nanograin matrix. The formation process of the nanocrystalline composite coating prepared by plasma spraying can be described as follows. When smaller size droplets spread on the substrate, they were quickly chilled to form nanosized equiaxed grains. Nanosized equiaxed and columnar grains were formed in the larger size spreading droplets due to the high chilling, large undercooling and non-equilibrium directional solidification of the ceramic melt.