Enhancing thermal transport and mechanical reliability in AlN ceramics through Y₂O₃-mediated optimization of 3YSZ co-additive effects

Pressureless-sintered AlN ceramics often suffer from a trade-off between high thermal conductivity and mechanical reliability due to oxygen impurities and grain-boundary phases. In this work, the effects of incremental Y₂O₃ addition (5–7 wt%) at a fixed 1 wt% 3YSZ on the phase evolution, oxygen chemistry, microstructure, and properties of AlN ceramics were systematically investigated. Increasing Y₂O₃ enhances oxygen scavenging from the AlN lattice and modifies Y–Al–O phase assemblages, while in-situ nitridation of ZrO₂ to ZrN suppresses excessive grain growth and promotes crack deflection. Thermal conductivity and mechanical strength are governed by the balance between oxygen removal, grain-boundary density, and secondary-phase distribution. An optimized composition, 6Y1Z, exhibits a high thermal conductivity of 193.7 W·m⁻ 1 ·K⁻ 1 together with a flexural strength of 465 MPa and a fracture toughness of 3.28 MPa·m 1 ᐟ 2 . Performance-map analysis indicates that this composition approaches a near-optimal balance among pressureless-sintered AlN ceramics, demonstrating an industrially viable route to high-performance AlN substrates.