DEFORMATION MECHANISMS IN A BINARY TI-48 AT.PERCENT-AL ALLOY WITH LAMELLAR MICROSTRUCTURE

The deformation mechanisms active in the gamma- and alpha(2)-lamellae of a Ti-48 at.%Al alloy during room-temperature and 800 degrees C tens ile loading have been determined by transmission electron microscopy. A marked change in the plastic behaviour of the alpha(2)-phase has bee n detected between room and elevated temperature, whereas the deformat ion mechanisms active in the gamma-phase remained the same at both tem peratures. At room temperature, plasticity in the alpha(2)-phase occur red only locally by prism plane slip of dislocations with Burgers vect ors parallel to [<11(2)over bar 0>] where cross-lamellar twins in the gamma-plane impinged on the (gamma/alpha(2))-interface. At 800 degrees C more homogeneous plastic behaviour of the alpha(2)-phase resulted f rom slip and climb activity of dislocations with Burgers vector compon ents parallel to [<11(2)over bar 0>] and parallel to both [<11(2)over bar 0>] and [0001]. The increased contribution to strain accommodation at 800 degrees C by the alpha(2)-lamellae coincided with a change in predominant fracture mode.