Microstructure and mechanical properties of as-cast quasibinary NiTi–Nb eutectic alloy

Abstract

a b s t r a c tNi 40 Ti 40 Nb 20 is reported in the literature as a eutectic composition in the quasi-binary NiTi-Nb system. Eutectic and near-eutectic alloys find applications in various fields, including hydrogen permeation, energy damping, and liquid phase bonding of NiTi structures. In this study, we examine a cast Ni-Ti-Nb alloy with the above eutectic composition. Prealloyed, near-stoichiometric NiTi powders and pure Nb powders are blended and heated above the eutectic temperature to create a melt with the eutectic composition. After solidification, the ingot shows some elemental segregation at its top and bottom, but a large middle region exists with a homogeneous eutectic structure. The eutectic has average composition of Ti-40.1Ni-19.6Nb at% and consists of Nb-rich lamellae (Nb-19Ti-10Ni) dispersed within a NiTi-rich matrix (Ti-41Ni-15Nb). Under monotonic compressive deformation, the eutectic alloy yields at 630 MPa, and then shows a linear hardening region, where both plastic and superplastic deformation are active, until a stress of 1080 MPa is reached at an applied strain of 14.7%. On unloading, some superelastic strain is recovered. Upon unloading during compressive load-unload cycling, the eutectic alloy exhibits approximately twice as much superelastic recovery as elastic strain recovery, regardless of the maximum cycle strain.

Hierarchical Eutectic Structure Enabling Superior Fracture Toughness and Superb Strength in CoCrFeNiNb0.5 Eutectic High Entropy Alloy at Room Temperature

“…Evidently, there are grain‐like colonial regions with an average size of 20–30 μm surrounded by the coarse lamella regions as the colony boundaries. Such a hierarchical structure is the result of a varying cooling rate in metallic melts, which can be controlled by tuning the melt chemistry and cooling rate . Further SEM imaging reveals that each colony consists of the fine lamella structures with the lamella orientation varying from colony to colony, as seen in Figure d.…”

Research on Shape Memory Alloys and Magnetorheological Fluids for Use in Pneumatic Actuators

“…where a 2 is a constant (measure unit K À1 ), A 1 f is temperature of terminating the austenitic phase and M 0 f is temperature of terminating the martensitic phase. Equations (19) and (20) make clear the existence of direct correlation between the temperature and the bending of the plate which describes its thermomechanical behaviour.…”

“…Eqs. (19) and (20) can be used for the calculation of bending in the plate containing SM elements and for the evaluation of minimum force which is necessary aiming to fix a certain shape of the plate. The numerical research has shown that force which is necessary for the counter-bending of plate varies from 370 to 135 N (it is equal to force being triggered by the plate), when temperature varies from 80 to 100°C.…”

“…One dimensional composite mathematical model of internal variables has been offered by Brinson et al [19,20].…”

“…This model quantitatively evaluates the absorption of deformation energy and allows predicting marginal load which is necessary for the beginning and the termination of a martensitic phase transformation induced by stress [6,19,20]. There, martensitic fracture variable is being decomposed into two components depending on stress and temperature.…”