Application of shape memory alloy

The characteristics of shape memory alloys were discovered in the early 1950s, and alloys of gold, cadmium, indium and thallium all have these characteristics.

Memory alloy has been used for pipe connection and automation control. The shell made of memory alloy can replace welding. The method is to enlarge the pipe end by about 4% at low temperature. When assembling, the sleeves are put together. Once heated, the shrinkage of the sleeve returns to its original shape, forming a tight connection. The hydraulic system of the U.S. Navy aircraft uses 100,000 of these connectors, and there has been no oil leakage or damage for many years. It is very convenient to repair damaged ships and subsea oilfield pipelines with memory alloy fittings. In some places where construction is inconvenient, make memory alloy pins and heat them to make holes. The end of the pin is automatically separated and crimped to form a one-sided assembly.

Memory alloy is particularly suitable for thermomechanical and thermostatic automatic control. Automatic opening and closing arm at room temperature has been made. It can open ventilation windows on sunny days and close automatically when the room temperature drops at night. There are many design schemes of memory alloy heat engine, which can work between two low temperature difference media, thus opening up new ways to utilize industrial cooling water, nuclear reactor waste heat, ocean temperature difference and solar energy. The current common problem is that the efficiency is not high, only 4%-6%, which needs to be further improved.

Shape memory alloys have also attracted considerable attention in medical applications. For example, the bone graft plate can not only fix two broken bones, but also generate compressive force during the restoration of the original shape, forcing the broken bones to connect together. Orthodontic wires, cerebral aneurysms, long clips for vasectomy, and support plates for spine correction are all activated by body temperature after implantation. Thrombosis filter is also a new kind of memory alloy product. After the corrected filter paper is implanted in the vein, the filter paper gradually returns to a mesh shape, thereby preventing 95% of blood clots from flowing into the heart and lungs.

An artificial heart is an organ with a relatively complex structure. The muscle fibers made of shape memory alloy match the elastic membrane ventricle and can simulate ventricular contraction. Now the pumping is successful.

Because memory alloy is a kind of "live alloy", by using its shape change at a certain temperature, various automatic control devices can be designed, and its application range is continuously expanded