Shape-memory NiTi-Nb foams

A new powder metallurgy technique for creating porous NiTi is demonstrated, combining liquid phase sintering of prealloyed NiTi powders by Nb additions and pore creation by NaCl space-holders. The resulting foams exhibit well-densified NiTi-Nb walls surrounding interconnected pores created by the space-holder, with controlled fraction, size, and shape. Only small amounts of Nb (3 at.%) are needed to produce a eutectic liquid that considerably improves the otherwise poor densification of NiTi powders. NiTi-Nb foams with 34-44% porosity exhibit high compressive failure stress (>1,500 MPa), ductile behavior (>50% compressive strain), low stiffness (10-20 GPa), and large shape-memory recovery strains. These thermomechanical properties, together with the known biocompatibility of the alloy, make these open-cell foams attractive for bone implant applications.