Interface mobility in Ni49.8Ti42.2Hf8 shape memory alloy

Abstract The ternary Ni49.8Ti42.2Hf8 shape memory alloy shows mechanical peculiarities compared with NiTi alloy. These are linked to (i) the distortion of the habit plane of the ternary alloy and (ii) the observed (001) mechanical twinning, which helps to accommodate plastic deformation in Ni49.8Ti42.2Hf8 and not in NiTi alloy. The distortion of the habit plane limits its mobility, evidence of which being brought here by internal friction. The (001) mechanical twinning causes the appearance of a very thin microstructure in martensite laths deformed by tension. A model is proposed as a possible mechanism giving birth to this supplementary mechanical twinning: repeated slips by a/2 on (001) planes would create translative (001) micro-twins coherent with the observed microstructure. These micro-twins may be produced by the dissociation of dislocations with the Burgers vector a.