Sliding wear behaviour of alumina coatings prepared from mechanically milled powders

There is a need for coatings to resist not only wear but also chemical attack and excessive heat. Alumina coatings were applied to type 304 stainless steel using the detonation gun method with high energy ball milled powder having an 83 nm average crystallite size. Coatings with varying amounts of partially melted (PM) and re-solidified (RS) alumina were obtained by adjusting the heat input and the gun-substrate distance. Deposition conditions which enhance the formation of thinner splats and nano-particulate alumina were found to improve the sliding wear resistance of the coatings when mated with an alumina ball under reciprocating test conditions. The observed lower wear rate of the coatings was due to the absence of brittle deformation of the layers and a lower friction coefficient. The deformation mechanism of the coatings was correlated with their microstructures and with hardness data from polished cross-sections.