From porosity-controlled to phase-controlled mechanics: Sintering-driven microstructural and fracture evolution in commercial dental 3Y-TZP

Three-mol% yttria-stabilized zirconia (3Y-TZP) is among the most extensively utilized materials in dental CAD/CAM systems, and its mechanical performance is directly governed by the final sintering conditions. In the present study, a commercial dental zirconia (Ceramill Zi) was sintered over the temperature range of 1200–1600 °C in 50 °C increments, and its densification behavior, phase evolution, microstructural development, and mechanical properties were systematically and concurrently evaluated. The results demonstrate that increasing the sintering temperature leads to progressive densification, with the relative density exceeding 99% at approximately 1400 °C. Beyond this temperature, the influence of open porosity on the mechanical response becomes markedly reduced, and the mechanical behavior is increasingly governed by grain-size evolution and phase constitution. Hardness and elastic modulus progressively approach saturation with further temperature increase, whereas indentation-derived fracture toughness exhibits a non-monotonic response, decreasing from approximately 5.42 MPa·√m at 1400 °C to about 4.72 MPa·√m at 1450 °C and subsequently increasing to approximately 5.44 MPa·√m at 1600 °C. This behavior is interpreted as the result of competing microstructural and phase-related effects, including grain growth, increasing cubic-phase fraction, and changes in the transformability of the tetragonal phase. Based on the integrated microstructural and mechanical analysis, the 1500–1550 °C range is proposed as a balanced processing interval for Ceramill Zi under the present experimental conditions, providing a favorable compromise among densification, phase constitution, grain-size evolution, hardness, elastic modulus, flexural strength, and indentation-derived fracture toughness.