SCALE OF MICROSTRUCTURE EFFECTS ON THE IMPACT RESISTANCE OF AL2O3

The impact resistance of alumina (Al2O3) is being investigated by indentation and single-particle-impact tests at the US Bureau of Mines. The primary aim of this research is to gain a better understanding of the mechanisms of material removal as a result of changes in the scale of damage relative to the scale of the microstructure. Preliminary spherical single-particle-impact and quasi-static indentation tests have focused on alumina with grain sizes of approximately 3, 7 and 13 mum, and results to date have shown that, although the crater diameter is not significantly affected by grain size, the deepest craters are produced on the aluminas with the larger grain size. The type, number and extent of crack formation are influenced by grain size. The fine-grained alumina yielded the shortest cracks for both impact and quasi-static indentations. No difference in the relative ranking of materials has been detected for different crack sizes, suggesting that the evolution of impact or indentation produced cracks is not influenced by R curve behaviour for the aluminas tested. Radial crack lengths produced by quasi-static indentation and impacts are similar in length for equivalent crater diameters. The impact crater diameters have been successfully described by an analytical expression.