THE COMPRESSION BEHAVIOR OF NIOBIUM ALLOYED GAMMA-TITANIUM ALUMINIDES

The underlying mechanisms behind the reported high strength of titaniu m aluminide alloys containing a large addition of niobium has been inv estigated by determining the flow stresses and activation parameters o f plastic deformation. It has been found that alloys such as Ti-45Al-1 0Nb (at.%) and Ti-45Al-5Nb have 1.25% flow stress values in compressio n of >800 MPa at room temperature and > 500 MPa at 1173 K. When compar ed with values from a more conventional alloy, Ti-47Al-2Cr-0.2Si, they represent a considerable increase in strength. However, the activatio n volumes after 1.25% deformation are very similar to those of convent ional alloys, particularly up to 973 K. This suggests that athermal di slocation mechanisms are responsible for the increased flow stress of the niobium containing alloys. By comparing the properties of the niob ium containing alloys with different binary alloys it has been shown t hat the high strength is solely a result of the reduced aluminium cont ent and that niobium plays no role in strengthening or work hardening. (C) 1998 Acta Metallurgica Inc.