DEFORMATION MECHANISMS IN AN (ALPHA+ALPHA-2) 2-PHASE TI-15 AT PERCENT AL-ALLOY AT ELEVATED-TEMPERATURES

Deformation characteristics of a two-phase Ti - 15 at.% Al alloy consisting of alpha-Ti (hcp) and alpha-2 (DO-19, Ti3Al) phases have been investigated at several temperatures between 300 K and 1173 K by means of compression tests and transmission electron microscopy. The two-phase samples were composed of homogeneously distributed ellipsoidal coherent precipitates of alpha-2 with a volume fraction of about 0.45. The 0.2 % offset yield stress was increased by about 1.5 times as high as that for the solution-treated samples below 873 K, but decreased gradually with increasing temperature. The deformation modes were classified into three types depending on the deformation temperature: the cutting mechanism operates up to 873 K, both cutting and climbing mechanism occur at a temperature between 873 K and 1073 K, and viscous glide of dislocations is preferred above 1183 K.