Large-strain Lüders-type deformation of B19' martensite in Ni₄₇Ti₄₉Nb₂Fe₂ alloy

In this study, a Lüders-type deformation with ∼40% strain of B19' martensite phase was observed in a Ni₄₇Ti₄₉Nb₂Fe₂ alloy at −50 °C. Such phenomenon was attributed to the nearly equal critical stresses of both dislocation slip and twinning, which result in the two deformation mechanisms co-operate concurrently. The large-strain Lüders-type deformation disappeared when the deformation temperature was away from −50 °C. This was probably due to the different temperature dependence of the critical stresses of dislocation slip and twinning. Owing to the huge Lüders-type deformation, the alloy exhibited a combination of high yield strength of 1105 MPa and large elongation of 55%, which was superb than those deformed at other temperatures.