Anelastic contributions and transformed volume fraction during thermoelastic martensitic transformations

Abstract

The internal-friction spectra of a thermoelastic martensitic transformation are usually obtained as a function of temperature with $\mathrm{T\ifmmode \dot{}\else \.{}\fi{}}\ensuremath{\ne}0$ and show three---phase transition, transitory, and intrinsic---contributions. This paper proposes a systematic method to analyze these internal-friction spectra. Indeed, two different procedures are derived. The first one, with the support of an isothermal spectrum $(\mathrm{T\ifmmode \dot{}\else \.{}\fi{}}=0),$ allows one to decompose the internal-friction spectrum into its three contributions and in addition to calculate the volume fraction of transformed material. The second one is based on an iterative process, and allows one to separate the intrinsic term from the other two contributions directly related to the martensitic transformation, and to calculate the volume fraction of transformed material, without the aid of an isothermal measurement. This method is successfully applied to a thermoelastic Cu-Al-Ni shape-memory alloy. Then, the dependence of the phase transition term on the volume fraction of transformed material is found. This allows us to reject the models proposed to explain this term that do not take into account this dependence.