Porous shape-memory NiTi-Nb with microchannel arrays

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 + Nb 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. Finite element modeling (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 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. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.