If it is placed in a press with too little force, the spring comes out of the die unchanged. With too much force, the metal breaks into fragments. Using oil as a cooling lubricant and taking a step-wise approach to altering the alloy, however, allows it to be fashioned into particular shapes. One unique use of nitinol occurs in cardiac surgery. Surgical tools made of nitinol can be bent up to 90 degrees, allowing them to be passed into narrow vessels and then retrieved.
The tools are then straightened out in an autoclave so that they can be reused. Many of the technical problems of working with nitinol have been solved, and manufacturers of the alloy are selling more than twenty different nitinol products to countless companies in the fields of medicine, transportation, consumer products, and toys.
Nitinol toys include blinking movie posters, butterflies with flapping wings, and dinosaurs whose tails move; all these applications are driven by a contracting bit of wire that is connected to a watch battery. Orthodontists sometimes use nitinol wires and springs in braces because the alloy pulls with a force that is more gentle and even than that of stainless steel, thus causing less pain.
Nitinol does not react with organic materials, and it is also useful as a new type of blood-clot filter. Best of all, however, is the use of nitinol for eyeglass frames. If the wearer deforms the frames by sitting on them and people do so frequently , the optometrist simply dips the crumpled frames in hot water and the frames regain their original shape. At this point, the activity surrounding nitinol seemed to all but dry up and disappear.
Afterwards, there was little to no attention given to nitinol by major television networks for over twenty years.
This led to all kinds of conspiracy theories ranging from nitinol being kept for top secret government experiments to nitinol being an alien technology that was discovered in the Roswell accident. However, the reality is very different. Behind the scenes, material scientists were working hard to figure out HOW nitinol worked. In order to fully optimize a nitinol heat engine, it must be understood what happens when nitinol undergoes the shape memory effect.
This will be discussed in greater detail in chapter 2. Of course, this is a misnomer since nitinol is slightly more nickel than titanium. Once Nike began to use it in their Vision line of glasses, athletes everywhere began buying it up. Gone were the days of breaking your glasses on a regular basis just because you lived an active lifestyle.
You could sit on them, you could intentionally bend them, you could tackle someone in football, and they would just bounce back. These glasses would forgive those bumps and bangs over and over again—seemingly forever. People who broke their glasses every six months now could go several years on a single frame.
Once in place, the superelastic nitinol wire could withstand severe deformation and outlast stainless steel by an order of magnitude. Stainless steel, on the other hand, could withstand a deformation of just 0.
This made intravascular stents something that could be considered permanent, never needing replacement. Yes, strange as it may seem, our five cent coin is made from a metal that we are allergic to. Of course, this could potentially cause huge problems for patients if enough nickel were to dissolve out of the nitinol and into the bloodstream.
Since then, nitinol has replaced other alloys in just about every kind of implant in the human body. Researchers have found that it makes a great hip replacement material because the superelastic phenomenon damps out the vibrations caused by walking—greatly extending the useful life of a joint replacement.
Because of the broad spectrum use of nitinol in surgical implants, the medical field is the largest consumer of nitinol worldwide. The second largest consumer of nitinol being the eyeglasses industry. Nickel-titanium NiTi shape-memory alloys SMAs have been used in the manufacture of orthodontic wires due to their shape memory properties, super-elasticity, high ductility, and resistance to corrosion.
SMAs have greater strength and lower modulus of elasticity when compared with stainless steel alloys. The main disadvantage of alloy wheels is their durability. When impacted by the road, alloy wheels tend to bend and even crack more easily than tougher steel wheels. The aesthetic appearance of alloy wheels is also threatened as they are more easily prone to cosmetic damage.
Brittle materials are having BCC structure and they have the property to form Carbides which is very hard phase and so with increase in hardness of material its brittleness also increases. Though Carbides improve wear resitance and corrosion resitance it makes material extremely hard and so it brittles.
A small part of the actual alloy is machined off to create this finish. It is then lacquered over to prevent corrosion. You will be able to see if your wheel is diamond cut if on close inspection you see very fine lines created by the cutting machine and the appearance is very shiny. Who invented shape memory alloy? What is a shape memory alloy called? When was memory metal invented? Which metal alloy has a shape memory effect? What are the disadvantages of smart alloys?
Does gold have memory? What are the characteristics of shape memory alloys? Does metal have memory? Why are smart alloys useful? Why are alloys harder than Puremetals? How do you shape a memory alloy? Why are shape memory alloys useful? Who was the inventor of shape memory alloy? What happens when shape memory alloy is heated? How did NASA come up with the shape memory alloy? Who was the first person to discover shape memory?
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