Porous shape-memory NiTi-Nb with microchannel arrays

Abstract

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.

Interfacial Reaction Enhanced Liquid‐Phase Sintering of Metal/Oxide Soft Magnetic Composite

“…In the solid‐metal/liquid‐metal and solid‐non‐metal/liquid‐non‐metal systems, liquid‐phase sintering rivals solid‐state sintering in the enhancement of diffusion and mass transport, which ultimately promotes porosity elimination, grain growth and rapid densification at lower temperature. Typical examples include: permanent magnets (NdFeB , [ 26 ] SmFeTiV [ 27 ] ), electrical contacts (WCu [ 28 ] ), bronze (CuSn [ 29 ] ), shape memory alloys (NiTiNb [ 30 ] ), 2D materials (MXene‐H 2 O [ 31 ] ), aluminum alloys (AlCuMgSi [ 32 ] ), magnetic ferrites (MnZn, [ 11,33 ] NiZn [ 11 ] ), refractory ceramics (BN, [ 34 ] SiC [ 35 ] ), biological materials (Silica‐H 2 O [ 36 ] ) etc. In the solid‐non‐metal/liquid‐metal system, the objective of liquid‐phase sintering is to take advantage of reduced friction between solid particles and bonding at solid–liquid interface, which will balance strength and ductility in many cemented carbides (WCCo, [ 37 ] NbCTi, [ 38 ] TiBFe, [ 39 ] HfB 2 Ni [ 40 ] etc.).…”

Design of Menger sponge fractal structural NiTi as bone implants

“…has a self-similar fractal pore morphology [12,13]. Furthermore, the porosity and distribution of pores play an essential role in the mechanical properties [14][15][16][17]. The porous and cellular structures are usually divided into bending-and stretching-dominated ones.…”

Effects of Nb on the Microstructure and Compressive Properties of an As-Cast Ni44Ti44Nb12 Eutectic Alloy

“…Compared with other SMAs, such as iron-based and copper-based alloys, NiTi-based SMA have high strength and plasticity, good corrosion resistance, and excellent biocompatibility. Therefore, they have a great potential for biomedical applications [6][7][8][9]. As in typical NiTi-based ternary alloys, Nb plays an important role in NiTi-Nb alloys, because the addition of Nb increases the transition hysteresis of NiTi alloys [10,11].…”