Human progress is achieved through continuous exploration. In the past, when our industry was underdeveloped, the choice of industrial raw materials was very scarce. We can only choose the raw materials we can produce and use for us. It is impossible to choose which type of materials we want to use. However, with the continuous progress of scientific exploration, people's progress and breakthroughs in raw materials have also increased, A kind of material called memory alloy has attracted people's attention. Next, let's learn about this kind of memory alloy.
In the 1970s, an alloy with "memory" shape function appeared in the world material science. Memory alloy is a kind of special metal strip, which is easily bent. We put it into a glass jar containing hot water, and the metal strip rushes forward; Put it in cold water and the metal strip returns to its original state. In the glass jar containing cold water, lengthen a spring. When the spring is put into hot water, the spring retracts automatically. In cold water, the spring returns to its original state, while in hot water, it will shrink. The spring can be stretched and contracted for an unlimited number of times, and then retracted and opened. These are made of a smart metal with memory. Its microstructure has two relatively stable states. At high temperature, this alloy can be changed into any shape you want. At lower temperature, the alloy can be stretched, but if it is reheated, it will remember its original shape and change back. This material is called memory metal. It is mainly made of nickel titanium alloy. For example, a spiral superalloy, after high-temperature annealing, its shape is in a spiral state. At room temperature, it is forced to straighten with great force, but as long as the nickel titanium memory alloy wire heats it to a certain "abnormal temperature", the alloy seems to remember something and immediately returns to its original spiral shape.
Alloy spring:
The spring is made of TiNi shape memory alloy wire, which makes use of the one-way memory effect of shape memory alloy. After stretching, the original length of temperature sensing driving element can be restored with the increase of temperature. This spring is also a typical structural form of industrial shape memory alloy components. After stretching, take hot water or hot air as the heat source, and the temperature of returning to the original length is 65 ℃ - 85 ℃, and the original length is 80mm. The martensitic phase (i.e. the phase structure at low temperature, where the low temperature refers to room temperature) of the shape memory alloy is a soft phase, and the parent phase (i.e. the phase structure at high temperature, where the high temperature refers to 65 ℃ - 85 ℃) is a hard phase.
Purpose:
Memory alloys are widely used. For example, mechanical fastening pins and pipe joints, fire alarms, connectors and integrated circuit Brazing on electronic instruments and equipment, medical artificial heart valves, spinal correction rods, skull repair and plastic surgery, oral and dental orthopedics and jaw repair surgery. It will also play a magical role in communication satellites, color televisions, temperature controllers and toys. It will also become a new material in modern navigation, aviation, aerospace, transportation, light textile and other fronts. Memory alloy has been used in pipeline combination and automatic control. Casing made of memory alloy can replace welding. The method is to fully expand the pipe end by about 4% at low temperature. When it is assembled, it will be sleeved together. Once heated, The sleeve shrinks and returns to its original shape to form a tight joint. The hydraulic system of U.S. Navy aircraft uses 100000 such joints, and there has been no oil leakage or damage for many years. The damage of ships and submarine oil field pipelines can be repaired with memory alloy fittings, which is very convenient. In some parts with inconvenient construction, the pins are made of memory alloy and installed into the holes for heating, and their tail ends are automatically separated and curled to form single-sided assemblies.
The application of memory alloy in medical treatment is also very attractive. For example, the bone plate used for bone connection can not only fix the two sections of broken bones, but also produce compressive force in the process of restoring the original shape, forcing the broken bones to join together. Orthodontic wires for dentistry, long clips for ligating cerebral aneurysms and vas deferens, and support plates for spinal straightening are all started by the action of body temperature after implantation in the human body. Thrombus filter is also a new product of memory alloy. After the straightened filter is implanted into the vein, it will gradually return to a mesh, preventing 95% of the clots from flowing to the heart and lungs.
