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

Ceramics 2022, 5, 533–549.

Y2O3 at 3% mol partially stabilized Zr2O3 (3YSZ) porous specimens with variable open
porosity, from fully dense up 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.