Phase Field Study of the Microstructural Dynamic Evolution and Mechanical Response of NiTi Shape Memory Alloy under Mechanical Loading

Abstract

For the purpose of investigating the microstructural evolution and the mechanical response under applied loads, a new phase field model based on the Ginzburg-Landau theory is developed by designing a free energy function with six potential wells that represent six martensite variants. Two-dimensional phase field simulations show that, in the process of a shape memory effect induced by temperature-stress, the reduction-disappearance of cubic austenite phase and nucleation-growth of monoclinic martensite multi-variants result in a poly-twined martensitic microstructure. The microstructure of martensitic de-twinning consists of different martensite multi-variants in the tension and compression, which reveals the microstructural asymmetry of nickel-titanium (NiTi) alloy in the tension and compression. Furthermore, in the process of super-elasticity induced by tensile or compressive stress, all martensite variants nucleate and expand as the applied stress gradually increases from zero. Whereas, when the applied stress reaches critical stress, only the martensite variants of applied stress-accommodating continue to expand and others fade gradually. Moreover, the twinned martensite microstructures formed in the tension and compression contain different martensite multi-variants. The study of the microstructural dynamic evolution in the phase transformation can provide a significant reference in improving properties of shape memory alloys that researchers have been exploring in recent years.

Low-Hysteresis Shape Memory Alloy Scale-Up: DSC, XRD and Microstructure Analysis on Heat-Treated Vacuum Induction Melted Ni-Ti-Cu-Pd Alloys

“…However, more investigation is needed here, as experiments were not designed to primarily investigate on this effect. Furthermore, applying phase field studies that take into account multi-variants of martensite during the transformation, as they are emerging recently [40], could be taken in consideration to obtain a deeper understanding of the peculiarities in the B2-B19 phase transformation of Ni-Ti-Cu-Pd alloys.…”

Tantalum Alloy Welding: Does the Thermal Cycle Influence the Microstructure?

“…Commercial FEA packages (such as ANSYS) are not capable of directly correlating the effects of multi-phase or -domain structures when the transformation of heterogeneous microstructures takes place (if a thermal and/or mechanical load is applied). In recent years, the phase field method, based on the Ginzburg-Landau theory [18], or isothermal phase field models [19] (for shape memory alloys) have been applied. It is understood that these simplifications suppose a slight uncertainty about the precision of the model, but they are understood as sufficient for the given purpose.…”

Microstructural and Thermo-Mechanical Characterization of Cast NiTiCu20 Shape Memory Alloy

“…In recent scientific literature, interest was devoted to nano-structuration by ball milling and to preparation by sintering processes from powders [ 19 , 20 , 21 , 22 ]. Moreover, several studies involve theoretical calculations and simulations to correlate the macroscopic and functional properties of NiTi alloys to microstructural characteristics and to explore the martensitic path and evolution [ 23 , 24 , 25 , 26 ]. Concerning the damping properties, the grain size, martensite interface density, and defect structure are important internal variables and, in the case of NiTiCu, the Cu addition enhances the behavior of the NiTi system [ 5 , 27 ].…”