Unraveling the intrinsic phase evolution mechanisms behind strength and toughness improvements in Y-TZP

Abstract

The simultaneous achievement of high strength and toughness in ceramics remains a pivotal challenge in materials science. This study employs yttria-stabilized tetragonal zirconia polycrystals (Y-TZP) as a model system to unravel a novel synergistic strengthening-toughening mechanism governed by a multi-stage phase transition (T→O→M→M∗ superstructure). We demonstrate that this phase transition pathway enables stepwise strain energy release via an intermediate orthorhombic (O) phase and a resulting superstructure (M∗) through multiscale mechanical characterization methods and theoretical calculations. Remarkably, the material achieves a compressive strength of 4.5 GPa, alongside average flexural strength and fracture toughness of 784 ± 57 MPa and 9.5 ± 0.5 MPa m^1/2, respectively. First-principle calculations confirm the thermodynamic metastability of the O phase; thus, shear sliding along the [100]_O planes triggers monoclinic (M) twinning. Meanwhile, residual stress-driven atomic ordering culminates in M∗ superstructure formation. This strain-modulated phase transition mechanism enhances damage tolerance through self-regulated zigzag microstructural coordination and external stress redistribution. Our findings establish a new paradigm for designing advanced ceramics with low volumetric strain coordination, harmonizing ultrahigh strength and toughness at room temperature.