Erosion of aluminium-based claddings on steel by sand in water

This paper describes the slurry erosion of a range of HVOF deposited aluminium-based claddings on steel by sand in water. Coatings, approximately 300 μm thick, of commercially pure aluminium, eutectic aluminium/silicon alloy (12%) and of a novel composite incorporating alumina in this alloy have been tested, both as sprayed and as ground to remove surface roughness as far as possible. Angular silica sand of mean diameter 235 μm was used at a concentration of 2.5% in tapwater at impingement angles of 90° and 30° and a jet velocity of 27 m/s. Mass loss data and surface structure, as shown by electron microscopy and profilometry, are related to the test conditions, initial surface topography, material hardness and microstructure, especially porosity. They are discussed in terms of the mechanisms of erosion that occur in the different materials, with reference to microcutting and plastic deformation of the surface and to the effects of the alumina inclusions. The consequences of poor flow-out, leading to significant residual porosity of the composite cladding are discussed.