Influence of nanopowder sintering technology on crack resistance of tetragonal zirconium dioxide

The effect of various technological conditions of the preparation of samples from ZrO2 ceramics stabilized by various additives of yttrium oxide Y2O3 on the fracture toughness of the material has been investigated. Various modes of sintering of samples obtained by the method of co-deposition of nanopowders of zirconium dioxide ZrO2 and yttrium oxide Y2O3 were performed. An original technique for calculating the critical stress intensity factor from the test data of double cantilever beam specimens with a chevron notch by the wedging method is described. A characteristic feature of the loading diagrams for ceramics based on zirconium dioxide stabilized by additives of yttrium oxide is the presence of a stage of inelastic deformation, which develops without cracking. The mechanism of inelastic deformation is based on the phase transition of the tetragonal modification to the monoclinic modification of the crystal structure. For each mode, the values of fracture toughness characteristics are determined. Ceramics with the composition ZrO2 + 3 mol% Y2O3 (KIc = 6.86 MPa ∙ m1/2) exhibit the maximum crack resistance at a sintering temperature Tsint =1500°C for an hour. Deviation from the composition of 3 mol% Y2O3 reduces the fracture toughness. The increase in fracture toughness is favored by the grinding of the powder in a planetary mill. It is generally accepted that mechanical stresses arising at the top of a growing microcrack cause all round compression stresses, since the phase transformation is accompanied by an increase in the unit cell volume by 4%. This stabilizes the microcrack, slowing down its growth. This point of view was confirmed due to the well-known fact that when zirconium dioxide is cooled from 950°C to room temperature during the t → m transition, microcracks are intensively formed in the bulk of the material. However, when wedging a two-cantilever specimen with a chevron notch, the probability of the formation of compression stresses is small. This is also evidenced by the absence of cracking throughout the inelastic stage of material deformation. In the fine-crystalline structure of zirconium ceramics under loading, favorable conditions arise for the relaxation of shear stresses through the t → m transition.

1. Institute of Strength Physics and Materials Science SB RAS, 634055, Tomsk, Russia - Project № FWRW-2021-0009
2. the Volkswagen Foundation (VW) Research Funding Program “Trilateral Partnership between Ukraine, Russia and Germany” - Project a.z. 90355-1