Young׳s modulus, hardness and thermal expansion of sintered Al2W3O12 with different porosity fractions

Abstract Owing to their unusual thermal expansion properties ceramic phases from A 2 M 3 O 12 family have potential for applications as thermal expansion controlling fillers inside soft matrices or as materials with high thermal shock resistance when prepared in monolithic forms. In spite of this, the consolidation routes for achieving bulk forms with adequate microstructure and their mechanical and thermal properties are scarcely known and rarely studied. A prelaminar study on sinterability of Al 2 W 3 O 12 , a low thermal expansion phase, was accomplished for the temperature range between 850 °C and 1000 °C. Sintered samples with the porosity fraction between 0.1 and 0.25 were produced and their Young׳s moduli, hardness and thermal expansion studied through nanoidentation and dilatometry. Acoustic emission was employed for studying of microcrack formation during heating and cooling of sintered samples. Sintering study showed that the temperatures higher than 1150 °C may lead to the decomposition of tungstate due to WO 3 evaporation, while the sintering at the temperature of 850 °C provokes only small changes over grain size distribution. Hardness and Young׳s modulus decrease linearly in porosity range between 0.1 and 0.25. Young׳s modulus for fully dense Al 2 W 3 O 12 was calculated to be 70 GPa, illustrating that the phases from A 2 M 3 O 12 family are considerable softer than traditional ceramics. Microcrack formation was observed on cooling and heating, as well, causing the discrepancy between the intrinsic coefficient of thermal expansion (CTE), measured in powder form, and the CTE measured in bulk form. The key feature for future development of A 2 M 3 O 12 phases for thermal shock resistance applications is the better understanding of sintering processes in order to improve microstructure and reduce influence of microcracks over mechanical and thermal properties.