Novel calcium hexaluminate/spinel-alumina composites with graded microstructures and mechanical properties.

Calcium hexaluminate (CA₆) was incorporated into the matrix of magnesio aluminate spinel-alumina (MA-A) via infiltration of a porous preform fabricated from α-Al₂O₃ and MgO powders with a saturated calcium acetate solution and subsequent firing, forming CA₆/(MA-A) functionally composites with graded fracture toughness. Actually, the porous preform was partially and perpendicularly immersed (1/4 of its length) in the solution. Owing to the capillary action, the calcium acetate solution was absorbed into the porous preform, and the different absorption distance led to the graded solution concentration in the height direction of the porous preform. The in-situ formation of CA₆ conferred graded microstructures, as well as improved mechanical properties on the resultant composites. The CA₆ content decreased gradually along the solution absorption direction, i.e., from one end [CA₆/(MA-A) region] immersed in solution to the other end [MA-A region], reducing evidently the formation of layered structure along the direction, while increasing gradually the formation of spherical alumina particles. The CA₆/(MA-A) region had a better toughness that could prevent the crack propagation and improve the spalling resistance. Meanwhile, the MA-A region could provide structural support, because of the higher Vickers hardness and density. [ABSTRACT FROM AUTHOR]