Influence of alumina powder size on mechanical properties of in-situ coated alumina fiber-reinforced alumina composites

Continuous alumina fiber-reinforced alumina-matrix composites were fabricated by hot-pressing. Fibers were coated by La-monazite, and matrix was prepared using the mean size of 7 nm and/or 180 nm alumina raw powders. It was observed that the powder size of matrix affected the properties of the composites. Composites using the nano-sized powder (7 nm) as matrix showed higher pseudo-ductility, but lower maximum strength and density than those of the composite using the submicron-sized powder (180 nm) as matrix, regardless of the sintering temperature. Woody-type fracture due to fiber pull-out from matrix could be observed for all composites regardless of the size of powder for matrix after sintering at relatively lower temperatures. Nano-sized powder supplies a looser matrix than submicron powder, therefore, it should be corresponded to higher pseudo-ductility of the composites. Combination of the nano-sized and submicron-sized powder as matrix gives composites with highest strength as well as enough ductility.