Indentation fracture toughness of high purity submicron alumina

Abstract

High purity (99.99%) fine-grained alumina samples were prepared by colloidal techniques and sintered at temperatures varying from 1310 to 1550°C, yielding a final grain size ranging between 0.5 and 4.5 μm. Fracture toughness, KIC of the fine-grained alumina so prepared was determined by means of indentation test method. The KIC was found to increase with decreasing grain size. Scanning electron microscopy showed that the fracture mode in the submicron-grained samples was intergranular throughout whereas the coarser-grained samples displayed a mixture of inter- and trans-granular fracture mode. It is concluded that for brittle solids that fracture by cleavage, a way to improve its toughness is to decrease the grain size sufficiently to effect intergranular fracture. In the present study, a 25% increase in fracture toughness was obtained by such a technique. © 1998 Acta Metallurgica Inc.