A critical study of the erosion of an aluminium alloy by solid spherical particles at normal impingement

Abstract

Detailed observations of the mechanism of material removal in aluminium alloys eroded at normal incidence by spherical particles are reported in this paper. Eroded specimens were examined by scanning electron microscopy and were sectioned for metallographic examination. Important features observed included surface ripples of uniform wavelength and the formation of platelets on the surface. Beneath each surface examined was a layer, clearly delineated from the bulk material, with approximately four times the hardness of the bulk. This layer had a laminar structure and contained numerous embedded fragments of erodent particles. The layer was of relatively uniform thickness and was perforated in places by bulk material penetrating to the surface. Markers were placed beneath the surface of the specimens; after the specimens had been sectioned at different stages of erosion, the movement and distortion of the markers enabled the following mechanism of erosion to be identified. In the early stages of erosion, before a linear erosion rate is established, the subsurface microstructure is developed. Then, by a process akin to backward extrusion, bulk material is forced to the surface through fissures in the hard layer. The breaks in the layer coincide with peaks in the surface topography. The softer material is beaten into platelets by subsequent particle impacts, and wear results from the detachment of these platelets.