Determination of stress dependence of elastic and dissipative energy terms of martensitic phase transformations in a NiTi shape memory alloy

Abstract

It is illustrated, that our method [1-3] (developed for the separation of pressure dependence of the elastic and dissipative energy terms) can also be applied for the determination of stress-dependence of the non-chemical (elastic and dissipative) free energy contributions to the martensitic phase transformations. For this the results of Tanaka et al. [4], on the effect of constant applied tensile stress on martensitic phase transformations, in Ti-51at%Ni shape memory alloys (up to 400 MPa) have been used. Supposing that the volume derivatives of the elastic energies differ from zero at the martensite start (and austenite finish) as well as at the martensite finish (and austenite start) temperatures, it was shown that the dissipative energy terms were approximately zero for the B2-R transformation. For the R-B19' transition these energies are not negligible and are of the order of 1 x 10 7 J/m 3 . The stress dependence of the elastic energy terms of the B2-R and R-B19' transitions have also been determined from the original data. The results are consistent with the effect of hydrostatic pressure on the martensitic transformation measured in a similar alloy [21.