Mechanical Reliability and Thermophysical Performance of Transparent LiAlON Ceramics

ABSTRACT

Transparent lithium aluminum oxynitride (LiAlON) ceramics have attracted increasing attention because Li incorporation improves aqueous processability while modifying the crystal chemistry and microstructural evolution of conventional AlON. In this work, the mechanical reliability and thermophysical behavior of highly transparent Li _0.07 Al _2.76 O _3.64 N _0.36 ceramics were systematically investigated. Room‐temperature fracture behavior was systematically evaluated using Weibull statistics, subcritical crack growth (SCG) analysis, and strength–probability–time prediction. Thermophysical properties, including thermal expansion coefficient, specific heat capacity, thermal diffusivity, thermal conductivity, and temperature‐dependent Young's modulus, were measured over a wide temperature range. High‐temperature fracture strength and thermal shock resistance were further estimated using experimentally determined thermophysical parameters. The LiAlON ceramics exhibited a characteristic flexural strength of 254 MPa with a Weibull modulus of 4.33. Quantitative defect analysis indicated that surface machining damage, rather than residual porosity, dominated fracture initiation, suggesting a surface‐flaw‐controlled fracture behavior in the coarse‐grained microstructure. The SCG exponent was approximately 11, indicating moderate susceptibility to environmentally assisted crack propagation. Thermal conductivity remained slightly higher than that of conventional AlON despite Li incorporation, which is attributed primarily to reduced grain‐boundary phonon scattering associated with the coarse‐grained microstructure. Young's modulus decreased nearly linearly with temperature, and the predicted fracture strength remained approximately 190 MPa at 800°C. The present results suggest that the coarse‐grained microstructure simultaneously influences mechanical reliability and thermophysical performance through different microstructural pathways, highlighting the importance of balancing surface‐flaw tolerance and grain‐boundary scattering in the microstructural design of transparent structural ceramics for optical and high‐temperature applications.