Fracture mechanics and microstructure in NiTi shape memory alloys

Functionally graded NiTi shape memory alloys

In this study, in order to obtain a functionally graded material, NiTi strips were annealed at 350°C, 450°C and 550°C in a furnace using an assembly that allowed a temperature gradient along them, and their transformation temperatures were studied by Differential Scanning Calorimetry (DSC). Furthermore, the strips were bent at both ends and dipped into a water bath at room temperature which was...

Effect of microstructure on the fatigue of hot-rolled and cold-drawn NiTi shape memory alloys

We present results from a systematic study linking material microstructure to monotonic and fatigue properties of NiTi shape memory alloys. We consider Ni-rich materials that are either (1) hot rolled or (2) hot rolled and cold drawn. In addition to the two material processing routes, heat treatments are used to systematically alter material microstructure giving rise to a broad range of therma...

Phase-field modeling of martensitic microstructure in NiTi shape memory alloys

A phase-field model is developed to study the cubic to monoclinic martensitic phase transformation in nickel–titanium (NiTi) shape memory alloys. Three-dimensional phase-field simulations show the nucleation and growth of monoclinic B190 multivariants that form a polytwinned martensitic microstructure. Parametric studies demonstrate that mechanical constraints and crystallographic orientation g...

Atomistic study of nanotwins in NiTi shape memory alloys

Atomistic simulations are performed to study the structure and geometrical limit of nanoscale twins in NiTi shape memory alloys. We analyze compound twins as narrow as 1 nm, involving a few atomic layers. A novel nanotwinned structure is found, forming through the martensitic transformation of sublattices. We predict the temperatures of phase transformation, which are consistent with experiment...

NiTi Shape Memory Alloys, Promising Materials in Orthopedic Applications