Shape Memory Alloys- An Insight

To understand the importance of this topic, first we need to know it’s practical use and other applications. Shape memory alloys (SMAs) are an unique class of multi-functional materials that have the ability to recover large deformations or generate high stresses in response to thermal, mechanical and electromagnetic stimuli.They display two distinct crystal structures or phases: Martensite and Austenite. Determination of their phase depends on temperature and internal stresses (which play a part in super-elasticity). Martensite exists at lower temperatures and Austenite at higher temperatures.When a SMA is in Martensite form, the metal can be easily modified into any shape. Alloy on heating, goes through transformation from Martensite to Austenite, after which they convert themselves back to Martensite as Austenite is not stable at room temperature and systems are more stable at lower temperatures. Memory transfer temperatures can be altered by slight changes in composition and by slight changes in heat treatment. This material is a lightweight, solid-state alternative to conventional actuators such as hydraulic, pneumatic, and motor-based systems. Shape-memory alloys have applications in robotics and automotive, aerospace and biomedical industries. This article concentrates on the applications of SMAs , Research and development of shape memory alloy at NASA Glenn provides us information over its current and future progress. SMA actuators can generate motion in 1D (wires), 2D (bending of bar) or even motion in a more complex 3D (springs, honeycombs). Presently, the material most used for their development involves NiTi-based high temperature SMAs. On addition of Pt, Pd, Au, Hf and Zr have said to increase their transformation under stress free conditions, eg: NiTiPd and NiTiPt show work output and their ability to undergo repeated thermal cycling under load without undergoing permanent deformation on de-twinning stress of Martensite and resistance to dislocation slip of individual phases. SMA actuators continue to achieve steady growth in safety valves for both consumer and industrial applications. New actuator applications include a thermal interrupter for protecting lithium ion battery from uncontrollable thermal runaway. Research and development activities continue in vibration and damping principles. Employing either passive or active means are well proven but the commercialization has been slow to develop. Active tuning of resonance frequency and seismic vibration controls may find their niches in the near future. The use of super-elastic SMA components (in eyeglasses) for the nose piece (bridge) and ear pieces (temples) provide improved wearer comfort as well as great resistance to accidental damage. Smart materials and adaptive structures are now common and are used widely. Mainly their use is now concentrated over aeronautical and space structures.
Various examples include; To compensate for the use of hydraulic systems that operate most of the parts in aircraft, SMA actuators are incorporated for more efficiency and compactness, making their wings “smart” that requires only and electric current for movement. In order to expand their applications, further developments are needed to increase their reliability and stability and to address processing, testing and qualification needed for large-scale commercial application of SMA actuators.To conclude, Manufacturing products using advantages of SMAs with its memory property is also envisioned for use as car frames, engine cooling, carburetor, engines in cars and aircraft, electrical generators that utilize mechanical energy, lubrication controls and other automotive applications. Research using this particular material is carried out in various fields including robotics and material science department hence providing us with a brighter future over transformation from a destructed pattern to it’s original best form.