Mechanisms of plasticity and fracture of partially lamellar titanium aluminum

The deformation and fracture mechanisms active in the gamma- and alpha(2)-p hases of a binary Ti-48 at% Al intermetallic compound during tensile loadin g at room temperature and 800 degrees C have been determined by scanning an d transmission electron microscopy. A change of the dominant fracture mode from transgranular at room temperature to mostly intergranular at 800 degre es C has been observed. At both room and elevated temperature the gamma-pha se accommodated most of the strain by activation of essentially the same mo des of dislocation slip and ordered twinning, whereas a profound change in the plastic behavior of the alpha(2)-phase has been detected. At room tempe rature the alpha(2)-phase exhibited inhomogeneous slip of < a > dislocation s, b = < a > = 1/3 <11 (2) over bar 0>, on both {1 (1) over bar 00} and {(2 ) over bar 201}, whereas < c >-component dislocations, e.g. b= < 2c+a > = 1 /3 < 11 (2) over bar 6 >, have not been observed. After straining at 800 de grees C the a2-phase contained more uniform, denser populations of < a > di slocations, and notably also < c >-component dislocations. Climb occurred i n both phases during tensile tests at 800 degrees C. Tt has been proposed t hat the observed change in fracture mode may in part be related to the redu ction in the plastic incompatibility between the two phases due to the incr eased level of plasticity exhibited by the alpha(2)-phase at 800 degrees C. (C) 2000 Elsevier Science Ltd. All rights reserved.