Fracture resistance of 8 mol% yttria stabilized zirconia

Abstract

Anin situ technique for the assessment of fracture resistance employing double cantilever beam (DCB) specimens was developed in the present study. The side-grooved DCB specimens were loaded with pure bending moments in a specially designed and fabricated test fixture which went inside the specimen chamber of a scanning electron microscope. The study as conducted on a 8 mol% fully stabilized cubic phase yttria (Y₂O₃) stabilized zirconia (YSZ) ceramic. The powder processed sheets were sintered at 1600°C for 2 h in a zirconia tube furnace. The mode I applied energy release rate, G_I was determined for both pure YSZ and treated YSZ. Two sets of experiments were conducted for the complete characterization of the ceramics. Three fracture toughness values were determined for the pure and treated ceramics, viz. (i) at the onset of the crack initiation,G _ic, (ii) at the arrest of a subcritical crack, G_ia and (iii) at the onset of the fast fracture,G _if. Two analyses of the experimental data were carried out, viz. method of extrapolation and statistical analysis. In case of the pure YSZ, a transgranular mode of the stable crack growth was identified to be predominant. The porous coating treatment appeared to have positive effects as the crack initiation resistance increased due to electrode layers. The stable crack growth behaviours of the ceramics were investigated by monitoring the crack growth velocity as a function of appliedG values. The results obtained were of direct significance in designing and fabrication of SOFC stacks.