Fracture toughness and slow crack growth behaviour of metal-proton conducting ceramic composites

The fracture toughness and slow crack growth behaviour of two load-bearing metal ceramic components adopted in negatrode-supported electrochemical devices, namely Ni-BCZY27 and Ni-BCZY442, are investigated via double torsion technique.

The investigation showed that the two metal-ceramic composites are considerably less sensitive to slow crack growth when compared to oxide ceramics such as stabilized zirconia and alumina, with 𝐾_𝐼0/𝐾_𝐼𝐶 equal to approximately 0.8. On the other hand, they also showed lower fracture toughness than Ni-3YSZ, with Ni-BCZY442 and Ni-BCZY27 having a fracture toughness of respectively 1.74 and 3.04 MPa*m^1/2 for porosities equal to 25.8 % and 19.1 % respectively, compared to Ni-3YSZ reported in previous work with similar Ni content and porosity of approximately 30 % having a fracture toughness equal to 3.4 MPa*m^1/2. Furthermore, the analysis of samples presenting extensive barium depletion indicated fast fracture propagation upon application of loads significantly lower than the critical fracture load.