Alumina-based core containing yttria

A ceramic core for use in the investment casting of metals consisting essentially of, prior to sintering, about 80 w/o to about 86 w/o of a ceramic filler material and about 14 to about 20 w/o of a binder material, said filler material consisting essentially of about 85 w/o Al.sub.2 O.sub.3 particles, at least about 1 w/o of said filler material consists essentially of Al.sub.2 O.sub.3 particles having an average particle size of about 0.75 to about 3 microns, about 7 w/o Y.sub.2 O.sub.3 particles, about 2 w/o of a grain growth inhibiting agent, and the balance a carbon-bearing fugitive filler material, said ceramic core, subsequent to sintering, having a microstructure characterized by the presence of substantially unreacted Al.sub.2 O.sub.3 particles having a polycrystalline composition consisting essentially of 3Y.sub.2 O.sub.3.5Al.sub.2 O.sub.3 on the surfaces of said Al.sub.2 O.sub.3 particles.

A sintered ceramic core consisting essentially of substantially unreacted coarse Al.sub.2 O.sub.3 particles having a polycrystalline composition consisting essentially of 3Y.sub.2 O.sub.3.5Al.sub.2 O.sub.3 on the surfaces of said Al.sub.2 O.sub.3 particles.

A sintered ceramic core for use in the investment casting of superalloy materials containing a reactive metal, said core consisting essentially of substantially unreacted Al.sub.2 O.sub.3 particles having a polycrystalline composition consisting essentially of 3Y.sub.2 O.sub.3.5Al.sub.2 O.sub.3 on the surfaces of said Al.sub.2 O.sub.3 particles.