Simulation of recoverable strain variation during isothermal holding of the Ni51Ti49 alloy under various regimes

The aim of the present paper is to simulate the strain variation on isothermal holding of Ni-rich NiTi alloy under various regimes. The modified Likhachev-Volkov microstructural model and a new Nelder-Mead algorithm for the determination of the model parameters were used. To determine the model parameters, the experimental data obtained during holding of the Ni51Ti49 alloy under a stress of 200 MPa were chosen. Using these parameters, the strain variation on holding of the NiTi alloy under a stress in two regimes was simulated. It was shown that the modified Likhachev-Volkov microstructural model allowed one to calculate the isothermal strain variation on holding after cooling under a stress (Regime 1) and a good correlation between the theoretical and experimental results were found. At the same time, the simulation of the strain variation on holding after active deformation (Regime 2) did not fit to experimental data because the model did not consider the difference in the stored elastic energy in two regimes. It was shown that a decrease in the elastic energy stored during the transformation increased the strain during holding under a stress after active deformation and made the simulated curves to be close to the experimental.