Titanium aluminum intermetallic compound is a possible candidate for a high-temperature structural material, except for a problem of lack of room-temperature ductility. Recently, this problem was found to be overcome possibly by the addition of Mn, but this mechanism has not been fully understood yet. In order to understand the fundamental mechanism of the ductility improvement by Mn addition, microanalyses have been carried out. The results are as follows. Twin structures in a TiAl intermetallic compound in the as-cast state can be eliminated by high-temperature annealing, while those in Mn-added TiAl are thermally more stable and exist even after annealing for 86.4 ks at 1273 K. The reason for this thermal stabilization of twin structures is considered to be due to the pinning effect of twin dislocations by Mn addition. The enhancement of twin deformation in TiAl by Mn addition is regarded to be caused by two factors. One is the stabilization of twin partial dislocations, becoming the nucleation sites for twin formation. The other is the decrease in stacking fault energy, which makes twin deformation energetically easier.
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