Exploring the consistency of fracture toughness in stabilised zirconia ceramics with progressive dopant concentrations

This work presents a systematic study of the trend and relationship between indentation toughness and dopant concentrations in stabilised zirconia ceramics (calcia, yttria, and ceria stabilized). Influence of dopant concentrations on the mechanical properties of zirconia ceramics, focusing on optimizing fracture toughness through phase stabilization and grain size control has been discussed. Three dopant systems, e.g., yttria (2–4 mol.%), calcia (3.25–4.5 mol.%), and ceria (10–12 mol.%) were explored. Fracture toughness (K_IC) was determined using the Vickers Indentation Fracture (VIF) method and calculated through the Niihara equation for Palmqvist cracks. Elastic modulus values of 210 GPa for yttria-stabilized (YSZ) and calcia-stabilized (CaSZ) zirconia, and 190 GPa for ceria-stabilized tetragonal zirconia polycrystal (Ce-TZP) ceramics were considered. Studies with CaSZ ceramics revealed that toughness values remained unchanged across doping concentrations of 3.25, 3.5, and 3.75 mol.%, in contrast to traditional trends of toughness data in zirconia ceramics. The YSZ and Ce-TZP stabilized zirconia ceramics showed significant reductions in tetragonality and toughness with increasing doping levels, while CaSZ retained the tetragonal phase with minimal structural distortion. Additionally, 10.5 mol% Ce-TZP exhibited exceptional fracture toughness of ∼19 MPa√m, surpassing conventional benchmarks. CaSZ ceramic displayed a very fine microstructure with grain size in the range of 100 nm. The degradation of toughness values with doping concentration was correlated to numerous factors, e.g., grain size, reduction in tetragonality, appearance of a softer t’ phase etc.