On the fracture behaviour of niobium-alumina castables

The present study addresses the characterisation of niobium-alumina composites in terms of their fracture behaviour. Fine-grained Nb-Al2O3 composites with a niobium content of 60 vol% and produced from different alumina sources (tabular alumina or white fused alumina) were prepared by castable technique. The sintered castables were tested for their sensitivity towards subcritical crack advance, their R-curve behaviour, and the work of fracture. All properties were derived from slow, cyclic four-point flexure tests at room temperature, which allowed for the initialisation and the manual and automatic control of a stable growing crack. Overall, the investigated composites showed measurable R-curve behaviour and were more sensitive towards subcritical crack damage than pure alumina.