Lateral Cracks and Microstructural Effects in the Indentation Fracture of Yttria

Abstract

The fracture properties of three polycrystalline Y2O3 materials: one fully cubic phase, one containing an Al2O3 grain‐boundary phase, and one containing hexagonal phase, were examined by indentation over a wide range of contact loads. The two former microstructures displayed tendencies at large indentation loads to radial crack lengths shorter than those extrapolated from the ideal response at low loads. The deviations correlated with the development of lateral cracks at the larger contacts, rather than with any observable change in the interaction between the cracks and the microstructure. After taking the lateral crack influence into account, the toughness of all three materials was estimated to be constant over the range of crack lengths studied, in contrast to the phenomena observed in similar grain size noncubic materials and inferred from earlier fractographic studies. The toughness of the partially hexagonal material was estimated to be 50% greater than the cubic materials. The general phenomenon of partitioning energy into lateral cracks at the expense of radial cracks at large indentation loads has been characterized by a lateral crack development parameter, LD, which varies from 0 to 1 as lateral cracks progressively develop and remove material. Copyright © 1990, Wiley Blackwell. All rights reserved