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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.

Porous NiTi-Nb containing a 3D array of orthogonally interconnected microchannels was created via a novel powder metallurgy process combining: (i) Mg ribbon scaffold construction, (ii) slip casting of NiTi+Nb powder blend within the scaffold, (iii) Mg scaffold vacuum evaporation, and (iv) NiTi liquid phase sintering. The later stage was achieved by creating small amounts of quasi-binary NiTi-Nb liquid eutectic, which wicked between NiTi particles and bonded them together while leaving 28 vol.% of residual pores. These hierarchical porous structures have a total porosity of 30-53%, an effective stiffness of 5-9 GPa, and a yield strength of 20-80 MPa. They exhibit the shape memory effect, with 3% strain recovery after 7% compressive deformation upon multiple load-unload cycles. FEM is used to model the anisotropy of these structures, as well as to probe the strain distributions on a microscopic level. Mechanical anisotropy was also present in FEM of all structures, though more pronounced in structures with high microchannel volume fraction. With mechanical properties between those of trabecular and cortical bone, these structures are of great interest for bone implant applications.

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