Effect of grain size on wear behaviour of alumina cutting tools

Abstract

Pure alumina inserts with grain sizes of 0.83, 2.94 and 6.33 μm were produced by slip casting and pressureless sintering. They were used to turn medium carbon steel in dry, continuous cutting conditions, at a cutting speed of 450 m min -1. Examination of the flank face showed that the flank wear land was characterized by long and parallel ridges at short machining times, with the ridges becoming wavier as the grain size of the insert increased. The initial volume flank wear rate increased with increasing grain size of the insert and is consistent with grain spallation being the primary wear mechanism, although the wear rate was moderated by the subsequent smearing of spalled grains onto the tool surface by single glide. After the attainment of a critical width of flank wear land, a transition in wear feature to a two-zone wear feature with spikes nearer the cutting edge and ridges further away occurred; shortly after which the volume flank wear rate decreased appreciably. A similar two-zone wear feature was also observed on the crater of the tool even with short machining times. Although the size of the spikes observed in the crater varied with the grain size of the insert, crater wear rate, expressed as time rate of change of the maximum crater depth, is grain-size independent. This is because the maximum depth of the crater occurred in the region covered with spikes, where material loss is controlled by plastic deformation-induced necking of asperities, a process known to be grain-size independent.