The microstructure and thermomechanical behavior of Ti₅₀Ni₄₇Fe_2.5Nd_0.5 shape memory alloys

This work presents a study of a novel Ti₅₀Ni₄₇Fe_2.5Nd_0.5 shape memory alloy by EPMA, E-R analysis and tensile tests. Structural characterization shows the alloy consists of TiNiFe matrix, Nd₃Ni and Ti₂Ni intermetallic compounds with Fe solute. The latter two phases are well distributed in the matrix. Compared with Ti₅₀Ni_47.5Fe_2.5 alloys without rare earth Nd, the novel alloy does not change the two-stage martensitic transformation behavior, however, characteristic temperatures increase rapidly. The critical stress needed for inducing martensitic transformation is near linear relationship with the increasing of the testing temperature above M_s, which is in good agreement with Clausius-Clapeyron equation. The novel alloy exhibits an improved shape memory effect as a consequence of precipitation strengthening and the maximum recoverable strain attains to 7.8%.