J. Am. Ceram. Soc., 78
Effect of glass additions on the indentation-strength
behavior of alumina
Heather L. O'Donnell,
Motorcoils
Manufacturing Co,
Desiderio Kovar and
Michael J. Readey
Department of Materials
Science and Engineering,
ABSTRACT
The impact of small calcium aluminosilicate (CAS) glass additions on the microstructure and flow tolerance of alumina ceramics was examined, and the findings compared to a high-purity alumina. The high-purity alumina specimens were dense with microstructures comprising of a uniform grain size distribution and equiaxed grain morphology. Adding only 1 wt% glass phase led to a bimodal grain size distribution having large, elongated grains within a fine-grain matrix. Indentation-strength tests suggested improved flaw tolerance with the bimodal microstructure, although both materials had nominally identical average grain size. Observations of crack paths exhibited a greater propensity for bridging in the glass-containing alumina because of the presence of coarse, elongated grains and perhaps a lower grain boundary toughness. Nevertheless, crack extensions take place transgranularly when the size of the coarsest grains become too large. This indicated that an optimum in flow tolerance will be obtained with an elongated grain morphology and intermediate grain size.