Influence of Porosity on R-Curve Behaviour of Tetragonal Stabilized Zirconia

Y2O3 at 3% mol partially stabilized Zr2O3 (3YSZ) porous specimens with variable open porosity, from fully dense up to similar to 47%, and their potential use as anode supports for new solid oxide cell designs were fabricated by tape casting. The stiffness, strength and fracture properties were measured to investigate the influence of porosity on mechanical properties. The evolution of Young's modulus and characteristic strength was evaluated by ball-on-ring tests. The variation of critical plane stress Mode I stress intensity factor with porosity has also been investigated and modelled from the results obtained from fracture mechanics testing. R-curve behaviour was observed in dense 3YSZ specimens and in porous 3YSZ compositions. The width of the transformation zone after fracture mechanics testing and the variation with porosity were investigated. The phases existing in the fracture zone were determined and quantified by Raman spectroscopy. It was found that the width of the transformation zone increased with increasing porosity. A new general R-curve model for 3YSZ based on the McMeeking-Evans equation is presented, which can be used to predict the behaviour of the R-curve as a function of porosity, simply by knowing the properties of the dense material and introducing in this equation porosity-dependent laws on the key properties that affect fracture toughness.