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Abstract

Ceramic composites containing weak interfacial boundaries included for the purposes of providing avenues for crack deflection with a resulting toughening of a ceramic body. Weak interfacial boundaries are created between constituents of the composite, such as matrix phases and any continuous and/or particulate reinforcements, and tungstate, molybdate, tantalate, and niobate compounds of the general formula ABO.sub.4. For tungstate and molybdate compounds of the general formula ABO.sub.4, B represents tungsten or molybdenum, and A represents a divalent cation. For tantalate and niobate compounds of the general formula ABO.sub.4, B represents tantalum or niobium, and A represents a trivalent lanthanide series cation. The ABO.sub.4 tungstate, molybdate, tantalate, and niobate compounds may exist as barrier phases between the matrix and the reinforcements of the composite, or the ceramic body may contain discrete particulates, laminae, fibers, or whiskers of the ABO.sub.4 tungstate, molybdate, tantalate, and niobate compounds. In a preferred embodiment, the reinforcing phases of the composite is a continuous single or polycrystalline fiber; however, particulate or whisker reinforcements will also benefit by being separated from the matrix phases by an interphase of an ABO.sub.4 tungstate, molybdate, tantalate, or niobate. A non-brittle material may also be fabricated by creating multilayer laminar composites containing alternating lamina of the ABO.sub.4 compound and a second phase.

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