EFFECT OF POST-FORGING HEAT-TREATMENT ON THE MICROSTRUCTURE AND ROOM-TEMPERATURE TENSILE PROPERTIES IN TI-25AL-10NB-3V-1MO (SUPER ALPHA-2)

The room temperature tensile and fracture behaviour of super alpha 2 h ave been assessed as a function of a range of thermomechanical treatme nts. It has been shown that the best properties are obtained in sample s which have been forged in the beta phase field using cool dies, foll owed by aging at 800 degrees C for 2 h. These property measurements ha ve been correlated with the microstructural changes caused by the vari ous heat treatments. It has been found that the highest strength is as sociated with a two-phase structure of transformed beta phase containi ng about 17% primary alpha 2 and that improved fracture behaviour is a ssociated with a transformed fine Windmanstatten structure. It is conc luded that the room temperature tensile ductility improved by aging at 800 degrees C for 2 h, which reduces the dislocation density and the stress concentration caused by the heavy forging deformation within th e alpha 2 and B2 grains. Grain boundary alpha 2 films and the high Nb interface alpha 2 phases at primary alpha 2 and B2 matrix interfaces f orm after high temperature solution treatments. Also, these two kinds of alpha 2 phase result in low room temperature tensile ductility. Gra in boundary strengthening plays a dominant role in super alpha 2, and transgranular fracture is the main failure feature of this alloy.