Compatibility of the mechanical properties and thermal conductivity by the formation of a secondary phase in AlN ceramics: Application of multifractal analysis for the microstructure evaluation
Runa Miyata, Taito Ogiya, Yoshihiro Sato, Ryota Kobayashi, Fumio Munakata
Abstract
Aluminum nitride (AlN) ceramics exhibiting different secondary phase morphologies were fabricated using pressureless sintering at varying temperatures ranging from 1700 to 1850 °C, with a 5 mass% Y 2 O 3 sintering additive. Although the thermal conductivity of the AlN ceramics increased as the sintering temperature increased, the bending strength increased below 1800 °C and decreased above 1800 °C. The morphology of the secondary phase in the AlN ceramics demonstrated granular, reticulate, and linear forms in that order of the low sintering temperature. The value of generalized dimensions D q obtained by multifractal analysis increased below 1800 °C and decreased above 1800 °C. Higher values of D q indicated more complex morphology and higher dispersion, corresponding to the observed morphological changes in secondary phase and the increase or decrease in the value of D q . The sample sintered at 1800 °C had the highest D q value and the reticulate secondary phase, with a thermal conductivity of 160 W m −1 K −1 and a maximum bending strength of 324 MPa. These results suggest that the morphology of the secondary phase affects the bending strength of AlN ceramics and that the value of D q may be an indicator of the microstructure that achieves both thermal conductivity and mechanical properties.