Composition dependence and thermal hysteresis of martensitic transformations in Ni-Ti based shape memory alloys
Mechanical Properties of Metallic Materials and their Microstructural Origins
Final Report Abstract
The first part of the project is dedicated to the CALPHAD type Gibbs energy model extension which incorporates composition dependent elastic energy contribution. In the second part of the project it has been planned to apply such model to the martensitic transformation simulation in NiTi shape memory alloy in order to study the effect of composition dependent elasticity parameters on the transformation temperature hysteresis. To do so, a dedicated model for the elasticity moduli and equilibrium lattice parameter of a binary system have been proposed using the two sublattice model suitable for the description of NiTi system. Later, detailed analyses of the effect of composition dependence of elasticity moduli on the diffusion profile around the precipitates has been made first analytically, and then by performing the phase field simulations of Ni4 Ti3 precipitation in NiTi shape memory alloy. The icorporation of ab initio simulations of the elasticy parameters dependent on alloy composition around the stoichiometric composition of B2 phase allowed to determine the exact coupling parameter between elastic constants and the Ni content. Close comparison between the simulated and experimental results allowed to conclude that the stiffening effect of the B2 matrix with the increase of Ni content is responsible for the experimentally observed deep composition depletion zone around the Ni4 Ti3 precipiates which could not be decribed by purely kinetic effects. Due to the fact that a number of works on the phase field modeling of phase transformations in NiTi system (which was planned for the second period of this project) has recently been published by other groups, it would be more effective to apply the elasticity aware Gibbs energy model extension developed in this project to a different system, e.g. Fe-C, where the effect of chemo-mechanical coupling plays an important role during tempering of martensite.
Publications
- Solutal gradients in strained equilibrium, Phil. Mag. Lett. 93 (2013) pp. 680-687
R. Darvishi Kamachali, E. Borukhovich, O. Shchyglo, I. Steinbach
(See online at https://doi.org/10.1080/09500839.2013.847288) - DFT-supported phase-field study on the effect of mechanically driven fluxes in Ni4 Ti3 precipitation, Modelling Simul. Mater. Sci. Eng. 22 (2014) 034003 (14pp)
R. Darvishi Kamachali, E. Borukhovich, N. Hatcher, I. Steinbach
(See online at https://doi.org/10.1088/0965-0393/22/3/034003) - Incorporating the CALPHAD sublattice approach of ordering into the phase-field model with finite interface dissipation, Acta Mater. 88 (2015) pp. 156-169
L. Zhang, M. Stratmann, Y. Du, B. Sundman, I. Steinbach
(See online at https://doi.org/10.1016/j.actamat.2014.11.037) - Stress-strain sensitive Gibbs energy formulation of alloys, PTM 2015 conference, Whistler, Canada
O. Shchyglo, M. Mikolaychuk, I. Steinbach
