Dislocation microstructures in the individual domains of a 45º <¯321>-oriented polysynthetically twinned TiAl crystal were characterized after deformation in compression, at a strain rate of 3000/s, at 800C. Ordinary dislocation slip was found to be the predominant deformation mode for the deformation of domains [II], [V] and [VI], where the transmission electron microscopic foil normals were close to [0¯11], [01¯1] and [¯101], respectively. Mechanical twinning and super-dislocation slip were found to be complementary deformation modes which accommodated the deformation of these domains. Domain [I], where the transmission electron microscopic normals were close to [¯110], was observed to be only minimally deformed under the imposed deformation conditions. Although mechanical twinning dominated the deformation of domains [III] and [IV], where the transmission electron microscopic foil normals were close to [10¯1] and [1¯10], respectively, dislocation slip was also observed within non-twinned matrices. Most of the dislocations which were observed in domains [III] and [IV] were ordinary ½<110] dislocations. A correlation between the predominant deformation mode in an individual domain, and the mechanical response of the crystal, suggested that the yield stress of Ti-rich alloys was governed by ordinary dislocation slip or mechanical twinning or both; depending upon the sample orientation.

Deformation of a 45º <¯321> Oriented Polysynthetically Twinned TiAl Crystal at High Strain Rate and High Temperature. Z.Jin, G.T.Gray, M.Yamaguchi: Philosophical Magazine A, 2000, 80[1], 49-68