CREEP-BEHAVIOR OF DUAL-PHASE INTERMETALLICS BASED ON (TI,NB)3(AL,SI) AND (TI,NB)5(SI,AL)3

The creep properties of two dual-phase intermetallic alloys based on (Ti,Nb)3(Al,Si) and (Ti,Nb)5(Si,Al)3 with eutectic and hypoeutectic microstructures have been studied at 850 and 1000-degrees-C. The effects of selected microstructures on these properties have been also investigated. The creep results can be described in terms of classical power law creep. The creep stress exponents obtained lie between 3.4 and 4 and are within the range predicted for dislocation-controlled creep. The creep properties are completely determined by the (Ti,Nb)3(Al,Si) matrix. In the hypoeutectic alloys, precipitation strengthening of the matrix by fine secondary silicide precipitates occurs during creep and starting microstructures have only a marginal effect on the creep properties. In the eutectic alloys, where no precipitation strengthening of the matrix was observed, a microstructure consisting of fine and well aligned (Ti,Nb)3(Al,Si) laths with finely dispersed retained ordered beta-(B2) at the lath boundaries was found to be an optimum microstructure for creep resistance of these alloys.