Crystallography Study on the Internal Twinning of Ti–Nb‐Based Shape Memory Alloys

Abstract Internal twinning structure of several Ti–Nb‐based alloys is studied by coupling transmission electron microscopy (TEM) characterization and theoretical calculation based on the phenomenological theory of martensite crystallography (PTMC) and the theory of deformation twinning. The TEM study accords well with the theoretical calculations. Possible candidates that can serve as internal twins were predicted by the PTMC analysis, more specifically, (011) compound twinning for the Ti–16Nb–6Zr–1.2Mg alloy, while (011) compound and {111} type I twinning for the other alloys of the present study. The critical resolved shear stress for the {111} type I twinning is lower than that for the (011) compound twinning, because the magnitude of Burgers vector for the {111} type I twinning is more than six times as high as that for the (011) compound twinning. Thus, the internal twins observed preferably belong to the {111} type I twinning when both of the two twinning systems meet the criterion of PTMC.