Application of titanium nickel alloy wire in medical devices and surgical implants
As a new intelligent material, with the deepening of its research and the expansion of its application, the international industrial developed countries have formulated the material and test standards of memory alloy to standardize the material production and industrial application. Table 1 shows the influential American Standard ASTM f0263 (technical specification for Machinable TiNi shape memory alloy for medical devices and surgical implants) in the field of shape memory alloy materials. Since there is no standardized national technical standard for memory alloy materials in China, the national standard of "technical specification for NiTi shape memory alloy processing materials for medical devices and surgical implants" and industrial technical standards such as "terminology of medical memory alloy" and "technical specification for non vascular NiTi memory alloy interventional stent" have been drafted during the tenth five year plan, Other relevant standards will also be gradually incorporated into the preparation plan.
The anisotropy of TiNi binary shape memory alloy can be summarized as follows:
(1) Shape memory effect. The one-way memory effect of polycrystalline TiNi alloy can reach about 8%. In addition to the one-way memory effect, TiNi alloy can also produce two-way and whole process memory effects after certain heat treatment (or training), such as multiple heating cooling cycles, constrained heating and aging. The two-way shape memory effect has good stability, up to 6%. When the strain is less than 1%, The number of two-way memory cycles can reach millions of times.
(2) Hyperelasticity. From the stress-strain curve, hyperelasticity can be divided into linear hyperelasticity and nonlinear hyperelasticity. Nonlinear hyperelasticity is also called phase transformation pseudo elasticity. The hyperelasticity of TiNi alloy can reach up to 8%.
(3) Damping characteristics. Damping is a measure of vibration energy absorption by materials. Shape memory alloys have good damping characteristics because of the self cooperation of martensitic transformation and the anelastic migration of various interfaces (twin surface, phase interface and variant interface) formed in martensite.
(4) Corrosion resistance and biocompatibility. A large number of biochemical experiments at home and abroad on corrosion resistance, biocompatibility, cytotoxicity, carcinogenicity, hemolysis and sensitization show that TiNi alloy has better biocompatibility and corrosion resistance than stainless steel and cobalt chromium alloy, which is similar to pure Ti.
(5) Good mechanical properties. The yield strength of TiNi alloy at room temperature is about 200MPa, δ= 15%， α K = 38j / cm, breaking strength of 800 ~ 950MPa, and good plastic strain capacity. It can be processed into very fine wires and thin plates (diameter or thickness < 100) μ m)。