Effect of thermal exposure at 1200 °C and 1400 °C on microstructure and mechanical properties of reactive hot-pressed LaMgAl11O19 ceramics

The effects of thermal exposure on the microstructure and the mechanical properties were examined in the two reactively hot-pressed LaMgAl 11 O 19 (LMA) ceramics exposed to air at 1200 °C and 1400 °C for up to 100 h. After thermal exposure, neither phase decomposition nor transformation was observed, whereas the platelet-like grains broken into the finer equiaxed grains. The elastic properties were almost the same before and after thermal exposure. The hardness varied with exposure temperature and time at temperature. The flexural strengths of the two ceramics were nearly the same before thermal exposure, they significantly degraded after thermal exposure, however. For the sintered LMA ceramic at 1550 °C, the strength loss after 50 h and 100 h of exposure at 1200 °C was ∼23 % and ∼19 % respectively; while the loss after 50 h and 100 h of exposure at 1400 °C was ∼28 % and ∼21 % respectively. For the sintered LMA ceramic at 1600 °C, the strength loss after 100 h of exposure at 1200 °C and 1400 °C was ∼26 % and ∼30 %, respectively.