Fracture energy and crack growth in surface treated Yttria stabilized Zirconia for SOFC applications

The solid oxide fuel cell (SOFC) electrolyte, 8 mol% cubic phase yttria stabilized zirconia (YSZ), is coated and co-sintered with different electrode coatings. The fracture toughness and stable crack growth behavior of the treated YSZ are investigated and compared with that of pure YSZ. Two energy release rate (G) values, corresponding to crack initiation (Gi) and crack arrest (Ga) are used to characterize the cracking behavior. An improvement in the fracture resistance behavior by around 30–50% as compared with untreated YSZ is observed due to coating effects. Crack growth rate, da/dt, as a function of applied G is represented by a power law of the form da/dt=A (G)n, where A and n are the fitting constants. Interdiffusion of both Mn and Ni from coatings into the YSZ lattice during sintering appears to introduce residual stresses leading to an improvement in the fracture energy. The cracking mode for all the surface treated ceramics is identified to be predominantly transgranular in nature. Crack bridging appears to contribute for improved fracture toughness values in surface treated YSZ.