Study on the deformation mechanism of the martensitic Ti–16Nb high temperature shape memory alloy

Deformation mechanism of the martensitic Ti–16Nb shape memory alloy (SMA) with the non-conventional deformation response is investigated systematically by TEM. Such an alloy deforms mainly by twinning of the {111} type I, the 〈211〉 type II and the minor (011) compound twins. The deformation twins formed in Ti–16Nb SMA are responsible for the recovery strain upon heating, which are distinct from plastic twins observed to be formed in previous studies done in other SMAs. A few {111} and (002) stacking faults, either along or having an angle with the junction plane are formed near the boundary zone to accommodate strain and improve coherence of the twin boundary. In parallel, the {111} stacking fault led by Shockley partial dislocation plays an important role in the formation of such deformation twins. The {111} type I twin forms by continuous glide of the Shockley partial dislocation on the {111} lattice plane for 5 atomic layer, while the 〈211〉 type II twin forms by tiny modification of the matrix assisted by stacking faults.