Fracture Strength and Behavior of Pore-Free 3 mol% Y2O3:ZrO2 Ceramics

Hot isostatic pressing (HIP) was employed to fabricate 3 mol% Y2O3-stabilized ZrO2 ceramics with nearly pore-free microstructures. Zirconia ceramics containing residual pores (size: ~0.3 μm, <0.1%) exhibited a four-point bending strength of 1.11 GPa. In contrast, pore-free specimens achieved significantly higher strengths of 1.74 GPa for samples containing a small fraction of cubic grains and 2.29 GPa for specimens composed solely of the tetragonal phase. At the moment of fracture in the high-strength specimens, intense electrical discharges (visible sparks) were observed near the fracture origin. Post-fracture observations revealed that zirconia containing residual pores fractured into two pieces with relatively smooth fracture surfaces, whereas pore-free zirconia exhibited extensive fragmentation, producing highly irregular fracture surfaces. This behavior is likely associated with extensive rupture of Zr–O bonds within the crystal lattice during catastrophic fracture. These results demonstrate that the elimination of residual pores by HIP markedly enhances the attainable strength of zirconia ceramics and significantly alters their fracture behavior.