The influence of unshielded small cracks in the fracture toughness of yttria and of ceria stabilised zirconia

Abstract

The fracture toughness, Ric of two 3Y-ZrO2 with different grain size (177 and 330 nm) and 12Ce-ZrO2 were determined from a sharp micro-machined notch by Ultra-Short Pulsed Laser Ablation (UPLA) where a micro-cracked zone and non-transformed is generated in front of the notch. The notch plus the damage behaved as an unshielded edge surface crack. The fracture stress, sigma(f) of both 330 nm-3Y-ZrO2 and 12Ce-ZrO2 with similar short crack sizes were found to be comparable in despite of their different published R-curves. The results of K-IC were discussed in terms of the type of cracks induced and by using a simple R-curve model. It was concluded that for the development of high strength composites with 12Ce-ZrO2 as the matrix, the relevant K-IC that controls the sigma(f) with surface unshielded short cracks is much closer to the intrinsic K-IC than to the indentation K-IC or to the plateau K-IC of long cracks. (C) 2015 Elsevier Ltd. All rights reserved.