Influences of Ni content and porosity on mechanical properties of Ni–YSZ composites under solid oxide fuel cell operating conditions

Mechanical properties of nickel and yttria-stabilized zirconia (Ni–YSZ) anodes of solid oxide fuel cells undergo changes not only because of extrinsic conditions but also because of Ni, YSZ and pore proportions. In this study, elastic modulus and fracture behavior of Ni(NiO)–YSZ composites are investigated with changing Ni and pore volume fractions as the main parameters. NiO–YSZ composite stiffness at 800 °C monotonically increases with increasing NiO. However, the reduced form of Ni–YSZ shows drastic changes in elastic modulus and strength around 30 vol% Ni where the deformation behavior and fracture made transition from brittle-like to ductile. Both stiffness and strength show linear decreases with porosity, of which the degree of deterioration at 800 °C was duller than at room temperature. The influences of Ni content and porosity on elasticity are quantified using multiple-linear regression analysis. Pore volume fraction shows large negative effects on elasticity at room temperature in air. However, at 800 °C, Ni volume shows larger negative effects than pore volume under reducing atmospheres.