Shape Memory Alloy
Shape memory alloy (SMA) is a special variety of alloy which exhibits the unique ability to remember its original shape and this shape can be recovered even after significant deformation. The shape memory effect is achieved by a physical phenomenon known as martensitic transformation, which takes place when such alloys are heated and cooled, or when external forces such as pressure is applied to them. It all started back in the 1930s and 1940s when the metallurgists in the German and Russian armies were searching for materials that could be used in rifle barrels and other weapon applications that could handle the extreme temperatures and pressures, and retain their original shape. So basically, a shape memory alloy is an alloy that can “remember” its original shape after being stretched, bent or otherwise altered.
Shape memory alloys consist of two parts, namely a high-temperature phase known as austenite, and a low-temperature phase known as martensite. With its special properties, shape memory alloys have been used in various applications, ranging from micro-valves in waterjet cutting machines to components in aircraft and spacecraft. In this article, we will discuss the properties of shape memory alloys, and the applications in which these alloys can be used.
Shape memory alloys possess the unique ability to return to an “remembered” shape after being deformed, upon heating or pressure application. The return to the original shape is known as shape recovery, and can be controlled by selecting different alloy parameters such as composition, heat treatment and so on. This ability of these alloys to return to its original shape repeatedly has made them highly attractive for various applications.
The temperature at which the original shape is retrieved is known as the transformation temperature, and is usually between -100 oC and +150 oC depending on the composition and heat treatment of the alloy. The transformation temperature is the critical parameter that determines the useful temperature range of the alloy. For example, Ni-Ti shape memory alloy can be used as an actuator below -50 oC, while Cu-Al-Ni shape memory alloy can be used as an actuator between -40 oC and 280 oC.
Shape memory alloys also possess the useful feature of high strength to weight ratio. They typically have tensile strength ranging from 500 MPa up to 2600 MPa, and are several times lighter than conventional steel alloys. This can be very useful when applications that require strength and weight savings are taken into consideration.
Shape memory alloys have also been used in aircrafts, spacecrafts and other structural components, where their high strength and light weight can provide significant benefits in terms of weight reduction and structural integrity. They have also been used as actuators and mechanical couplings, where the shape memory effect can be used to control the deployment and orientation of components.
In conclusion, shape memory alloys are highly useful materials with many applications. They possess the ability to “remember” their original shape, even after significant deformation, and their other beneficial properties, such as their light weight and high strength, make them attractive for various applications in the aerospace, medical and consumer products industries.
