Engineering the porosity and superelastic behaviors of NiTi alloys prepared by an electro-assisted powder metallurgical route in molten salts

An Electro-Assisted Powder Metallurgical (EPM) route is able to prepare porous NiTi alloys with controllable porosities and pore sizes using nickel (Ni) and titanium (Ti) powders at a temperature ranging from 850 to 950 °C. Ammonium hydrogen carbonate (NH 4 HCO 3 ) was used as a sacrificial space holder to tailor the porosity and pore size of the NiTi alloy and its properties, i.e., elastic modulus , phase transformation temperature, shape memory effect, and superelasticity . By optimizing the synthesis temperature and content of the sacrificial space holder (0–30%), the porosity (41–75%), pore size (22–174  μm ), elastic modulus (4.77–0.87 GPa) and the recovery strain (>2%) of the EPM-NiTi can meet or are close to the standard of natural bone (porosity: 30%–80%, pore size: 100–600 μm, cancellous modulus: < 3 GPa, recovery strain: > 2%). Therefore, the EPM route is promising to prepare porous Ti-based alloys for implants.