Densification mechanism and microstructure evolution of large-sized Al₂O₃/YAG/ZrO₂ eutectic ceramics by hot-pressing sintering based on micro-nano eutectic-structured powders

This study resolved the long-standing trade-off between densification and microstructural coarsening in large oxide eutectic ceramics by fabricating bulk Al₂O₃/YAG/ZrO₂ ceramics (120 mm × 10 mm) with an ultra-high density (99.83 %) and retained submicron eutectic structure (spacing 0.408 µm). This achievement was enabled by an integrated innovative approach combining ultrafine micro-nano powders synthesized via laser floating zone melting at 300 µm/s (spacing 0.141 µm), ultrasonic wet sieving for interfacial purification, and low-temperature hot-pressing sintering at 1550 °C (150 °C below conventional temperatures), full densification within 45 min under 60 MPa pressure is enabled through a plasticity-dominated mechanism synergistically assisted by short-range interfacial diffusion. This plasticity-driven process, activated at 1200–1550 °C yielded ultrathin reconnected interfaces (0.7 µm thickness) while avoiding grain coarsening. The sintered ceramics exhibited exceptional properties: Vickers hardness 16.25 ± 0.46 GPa, fracture toughness 4.57 ± 0.81 MPa m^1/2, and flexural strength 516.3 ± 34.6 MPa at room temperature, significantly surpassing conventional sintered eutectic counterparts. High-temperature strength was retained at 290.1 ± 33.6 MPa at 1200 °C through suppressed lattice expansion and micro-nano plasticity. Remarkably, after 500 h exposure at 1400 °C, constrained microstructural coarsening (eutectic spacing evolved from 0.408 to 1.097 µm; Al₂O₃/ZrO₂/YAG phases limited to 0.651/0.406/0.434 µm) resulted in enhanced hardness (16.74 ± 0.37 GPa) and serviceable fracture toughness (3.09 ± 0.17 MPa m^1/2), demonstrating superior thermal stability via interface pinning effects. This work establishes a scalable plasticity-enabled low-temperature sintering strategy for manufacturing large-sized structural components with high performance in extreme environments.