Thermodynamic Modeling of plasticity-driven shifts in transformation temperatures of high-temperature shape memory alloys

Plasticity introduced by pre-straining in thermo-mechanical processes, like cold working, can result in significant changes in the transformation temperatures (TTs) of High-temperature shape memory alloys (HTSMAs). Modeling the shifts of the transformation temperatures is then a crucial stake for potential industrial applications. A continuum thermodynamics approach is proposed to model the shifts due to plasticity. The proposed model, derived from previous studies, estimates the new transformation temperatures of a HTSMA depending on the magnitude of accumulated plastic deformation. A backstress and plastic hardening energy terms are introduced within the expression of the Gibbs energy. These terms are directly expressed as a function of the accumulated plastic deformation. The model is calibrated using experimental data obtained with Differential Scanning Calorimetry (DSC) after compression of samples at room temperature. Assumptions are made regarding the volume fraction of retained martensite following deformation. An optimization of the hardening parameters is achieved to match experimental results. The developed model is able to describe the trends and shifts of TTs in the explored range of plastic deformations. This supports the fact that dissipative internal energies can explain the shifts of the transformation temperatures in severely deformed HTSMAs.