Microstructures, Defects and Deformation Mechanisms in Vanadium Modified Nb3Al

A transmission electron microscope study of the microstructure and defect structure in vanadium modified Nb3Al and its deformation mechanisms is presented. Two alloys are examined in which 20 and 40 atomic % V is substituted for Nb. The former alloy exhibits a microstructure containing a stable A15 phase and a metastable B2 phase which transforms to A15 upon heat treatment. The A15 grains contain defects similar to those observed previously in binary Nb3Al: i.e. large growth faults with R=1/4<012> and dissociated dislocations with a separation of =15nm and b=1/2<001> bounding a stacking fault with R=1/2<001>. The alloy containing 40 atomic % V consists only of an equilibrium B2 phase and exhibits greatly enhanced ductility. Slip occurs by the glide of dislocations with b=<111> on {011}.