Novel reaction-based processing of co-continuous ceramic-metal composites

Various ceramic-metal composites have been manufactured by either reaction sintering compacts of intensively milled powder mixtures or by reaction infiltration of porous oxide precursor bodies containing Fe2O3, ZrO2, TiO2, NiO, Nb2O5, etc. During the carefully controlled heating cycle in vacuum, the oxide reduction by Al to form the respective aluminide or metal aluminide alloys proceeds at relativeley low temperatures. By adding Al2O3 to the starting mixture, the final composition of such Al2O3-aluminide alloys (3A) can be adjusted in a nide compositional range. At metal or intermetallic volume fractions > 20 %, both phases are continuous, hence exhibiting an interpenetrating network similar to that of products of directed molten metal oxidation or reactive metal penetration processes. In this paper, systems based on TiAl, FeAl and NbAl3 are emphasized, though other 3A composites have also been investigated. Preliminary 4-point bend strengths of similar to 700 MPa in the Al2O3-FeAl system and similar to 500 in the Al2O3-TiAl system have been obtained. The most attractive aspects of 3A composites are their low-cost manufacturability, low specific weight, refractoriness as well as excellent oxidation and corrosion resistance.