Grain boundary pinning of polycrystalline Al2O3 by Mo inclusions

Nano- to submicron-sized Mo particulates were deposited on porous Al2O3 disks in gradient concentration. The disks were laminated and sintered in inert atmosphere, revealing Mo inclusions in various contents and pining phenomena of matrix Al2O3 grains. Detail quantification of the microstructure of Mo and Al2O3 grains was conducted with special emphasis on the effects of the ultrafine Mo grains. The results show that the contents (5 vol% and 16 vol%) and the size of Mo inclusion are the critical quantities for the formation of intergranular/intragranular Mo inclusions. The microstructural development of the Al2O3 composites is greatly influenced by the states of the inclusions. A discussion on the topological and two other models of microstructural development is presented.