Mechanism of grain refinement and growth for the continuous alumina fibers by MgO addition

Maintaining high mechanical properties and thermal stability of alumina fibers is a contradictory problem. In order to solve this problem, the effects of MgO addition on the microstructure evolution and properties of alumina fibers prepared by sol-gel were studied. The addition of MgO inhibited the formation of α-Al2O3 and the 2 wt% MgO addition was conducive to grain refinement, reducing the grain size from 227 nm to 162 nm and increasing the Weibull strength by 66%, up to 2.03 GPa with a peak value of 2.60 GPa. The grain growth exponent increased from 4 to 7.2 during the long-term holding at 1100 °C, indicating the better thermal stability of alumina fibers with 2 wt% MgO as well. The mechanism of MgO addition to the phase transition and grain growth of alumina fibers was further discussed.