Available online at www.sciencedirect.com ScienceDirect Journal of the European Ceramic Society 34 (2014) 3373–3378 Fracture behaviour of alumina-YAG particulate composites Radoslaw Lach ∗ , Kamil Wojteczko, Agnieszka Dudek, Zbigniew P˛ edzich AGH – University of Science and Technology, Faculty of Materials Science and Ceramics, Department of Ceramics and Refractory Materials, Kraków, al. Mickiewicza 30, 30-059 Krakow, Poland Available online 13 May 2014 Abstract Particulate composites of the Al 2 O 3 –YAG system were produced by precipitation of the yttrium oxide precursor in the aluminium oxide suspension. The solid state reaction took place during thermal treatment of the resulting powder and led to the creation of the YAG phase. This method allowed fine and homogenously distributed YAG inclusions within the alumina matrix to be obtained. The performed investigations involved determining of the critical stress intensity factor (K IC ), Vickers hardness and bending strength of the materials. The composites showed higher hardness (HV) than -Al 2 O 3 . The presence of YAG inclusion in the amount higher than 7.5 vol.% improved also fracture toughness when compared to polycrystalline alumina. In the case of the material with the best mechanical properties measurements of subcritical cracking were conducted and the threshold value of K IC (K I0 ) was determined. © 2014 Published by Elsevier Ltd. Keywords: Ceramic matrix composites; Alumina; YAG 1. Introduction Fracture toughness is usually characterized by measuring the critical stress intensity factor (K IC ). This factor describes frac- ture subjected to catastrophic crack propagation. However, slow crack propagation is one of the major reasons of a material destruction occurring under constant or cyclic load conditions. The course of the phenomenon of sub-critical crack growth (SCCG) depends on the stress level and also on the environment conditions (humidity). Parameters describing SCCG can be determined by different procedures. 1–6 Different experimental techniques can be applied to determine slow crack propaga- tion; Double-Torsion (DT), Double-Cantilever-Beam (DCB) and bending test with notched specimens. 7 In the available literature no investigations of the SCCG concerning Al 2 O 3 –YAG composites were presented. The only studies concern other composites with the -Al 2 O 3 matrix. 8 Aluminium oxide is one of the most abundant ceramic mate- rials, but relatively low fracture toughness limits its application. Thus, alumina is commonly reinforced with the second phase, ∗ Corresponding author. Tel.: +48 0 12 617 24 80. E-mail address: radek.lach@poczta.fm (R. Lach). and the aluminium–yttrium garnet (YAG) seems to be a seri- ous candidate for the role of such a reinforcing inclusion. Amongst three existing yttrium aluminates, YAG (Y 3 Al 5 O 12 ) contains the highest amount of aluminium and for that reason it is a thermodynamically stable phase in contact with Al 2 O 3 grains. The effective reinforcement with the isolated second phase particles could be achieved when these particles are evenly dis- tributed in the matrix. Such a distribution could be assured when crystallization of eutectic in the Al 2 O 3 –YAG system from the melt. This method was developed in the previous investigations by different authors. 9–16 Due to the complex nature of the crys- tallization process as well as high temperatures at which it takes place this method is expensive and rather not suitable for practi- cal applications. The sintering technique seems to be better from this point of view. The properties of such composites concern materials con- taining 2.5 wt.%, 17 or 5 and 25 vol.% 18,19 of YAG. Palmero et al. 19–21 who have been presented so far, prepared the compos- ite containing 5 vol.% of YAG by addition of yttrium chloride to the aluminium oxide suspension and its subsequent drying in a spray drier. In this work aluminium oxides, such as TM-DAR (Taimei Chemical Co., Japan) with 150 nm particle diameter and CR1 (Baikowski, France) with 0.6 m diameter, were used. The http://dx.doi.org/10.1016/j.jeurceramsoc.2014.04.020 0955-2219/© 2014 Published by Elsevier Ltd.