Fabrication and properties of porous NiTi shape memory alloys for heavy load-bearing medical applications

Porous NiTi shape memory alloys (SMA) with isotropic three-dimensionally interconnected pore structure, higher strength and less undesired Ti2Ni phases were fabricated using the improved self-propagating high-temperature synthesis (SHS) technique by means of providing the higher heat flux density for SHS reactions using the improved ignition technique and adopting the powder compacts with a larger volume-surface area ratio to reduce heat losses. The combustion temperature agrees well with the melting point of compound NiTi (1583 K) under the two preheating temperatures (623 and 673 K). The porous NiTi SMAs fabricated by such SHS technique have the higher compressive strength than that of the compact human bone and the similar Young's modulus to that of natural bones, which is anticipated for the ideal biomaterials used as the heavy load-bearing hard tissue implants. Moreover, the transformation temperatures of the porous NiTi SMAs could be easily adjusted to the suitable values for medical applications by heat treatment.