Formation of deformation twins in TiAl Original Research Article

Mechanisms have been proposed for the formation of fault-pairs in the L10 structure that involve both ordinary and super glide dislocations having co-planar Burgers vectors. These fault-pairs could serve as two-layer embryonic twins and twin thickening may occur by the coalescence of fault-pairs located at different levels within a slip band. The crystallographies of deformation twins are examined in as-processed TiAl by transmission electron microscopy and are correlated with that of slip required for the formation of fault-pairs. The correlations are consistent with the suggestion that fault-pairs maybe involved in the formation of deformation twins. Slip is observed ahead of a twin terminating within a crystal. Arguments are developed to rationalize this observation.