Dislocation dissociation and locking in intermetallics

Abstract

The recent observation that glide of coupled partial dislocations of b = ⅙⟨116⟩ in Ti₃Al appears to give rise to extended regions of antiphase boundaries on {111} suggests that there is a pinning mechanism which can result in the two identical ⅙⟨116⟩ partials responding differently to applied stress. The various modes of dissociation of superdislocations in intermetallic compounds, some of which give rise neither to stacking fault nor to antiphase boundary, are considered as methods of dislocation locking. It is suggested that for the specific cases considered, the relative lack of mobility of individual ⅙⟨116) dislocations in Ti₃Al and the lack of mobility of certain orientation dislocations in TiAl and Ti₃Al, could be influenced by such dissociations. In addition it is argued that the pinning required for the formation of extrinsically faulted dipoles on {111} in TiAl could also occur through the formation of these dislocation locks.