Deformation twinning intersections in a γ-TiAl-based Ti-50 at.% Al-2 at.% Mn-1 at.% Nb alloy deformed at room temperature

Abstract

Two types of deformation twinning intersections (which type depends on the orientation of the intersection line) have been observed by transmission electron microscopy in Ti-50 at.% Al-2 at.% Mn-1 at.% Nb alloy deformed at room temperature. It is found that the two types of intersection can be accomplished by basal or cubic plane slips or by shearing on the mirror plane in a barrier twin. For a type-I intersection, with the intersection line parallel to TB basal plane slip in the barrier twin, emitting M slip in the matrix. Another mechanism, namely straight penetration, is also suggested on the basis of experimental evidence. For a type-II intersection, with the intersection line parallel to TB cubic plane slip in the barrier twin. Possible dislocation reactions responsible for the observed features created by the deformation twinning intersections are proposed. The simple geometrical analysis can define well the intersection geometrically but cannot predict the reaction which actually occurs. It is suggested that a detailed calculation, taking account of effects of the external load and the stress built up by arriving Shockley partials is necessary in order to determine the conditions under which a reaction that actually occurs can be predicted.