Anin situstudy of twin propagation in TiAl

Anin-situobservation of mechanical twin nucleation and propagation in TiAl

“…N o fundamental investigations o n mechanical twin nucleation and propagation in TiAl have been carried out until the very recent work done b y Farenc, Coujou and Couret (1993) on twin propagation in TiAl. Farenc et ul.…”

Deformation twinning in TiAl: Effects of defect clustering

“…To the author's knowledge, there has been no direct experimental confirmation of the pole mechanism operating in the bcc or the fcc structure. Using an in situ straining TEM technique, Couret et al [30,41] observed direct evidence of a "polar twin source" in Ti-54A1 at 298 K. That is, a partial dislocation is pinned at a perfect forest dislocation and turns around emitting partial dislocation loops. Though indexing of Burgers vectors from the three series of micrographs was not possible, it was reported that the forest dislocation was most probably a screw superdislocation of Burgers vector of [101] type [30], not the pole dislocation of [110]/2 type [42].…”

“…A number of possible mechanisms for twin formation in 7-TiA1 have been suggested on the basis of dislocation dissociations or transformations in core structure [35]. These may be divided into the following three types: (a) expansion of a superlattice intrinsic stacking fault (SISF) loop splitting from a <101] superdislocation [34], (b) composite dissociation of <112]/2 superdislocation [38][39][40], (c) a pole mechanism anchored by a <110]/2 ordinary dislocation [41,42]. Since the two types of superdislocations also glide on the (111) plane at ambient temperatures, twinning partial dislocation of bt=[l12]/6 as a dissociation product may expand to form a twin embryo.…”

TEM observations of twin intersections in a Ti–47Al–2Cr–2Nb–0.1Y alloy compressed at room temperature

“…Deformation twinning and twin intersections play important roles in the plastic deformation of TiAl with the L1 0 structure [1][2][3][4][5]. Extensive efforts were devoted to studying their effects and formation mechanism [6][7][8].…”