Abstract
Shape memory alloys (SMA) are metallic materials which have the capability to return to some previously defined shape or size when subjected to appropriate thermal conditions. This is possible due to a phase change occurring at micro-structural level. Pseudo elasticity and shape memory effect are two important properties of these alloys.
The most commonly used SMA is Ni-Ti alloy called Nitinol. This alloy displays a strain rate of 8% as compared to 0.2% for steel.
SMA's have found a wide variety of uses especially in aero industry as actuators. Presently cost is the limiting factor but nevertheless with more research on such alloys it will be possible to increase their range of applicability.
Historic Background
The first recorded observation of the shape memory transformation was by Chang and Read in 1932. They noted the reversibility of the transformation in AuCd by metallographic observations and resistivity changes, and in 1951 the shape memory effect (SME) was observed in a bent bar of AuCd. In 1938, the transformation was seen in brass (CuZn). However, it was not until 1962, when Buehler and co-workers discovered the effect in equiatomic nickel-titanium (NiTi), that research into both the metallurgy and potential practical uses began in earnest. Within 10 years, a number of commercial products were on the market, and understanding of the effect was much advanced. Study of shape memory alloys has continued at an increasing pace since then, and more products using these materials are coming to the market each year
The most effective and widely used alloys include NiTi (Nickel - Titanium), CuZnAl, and CuAlNi.
What are Shape memory alloys?
The term Shape Memory Alloys (SMA) is applied to that group of metallic materials that demonstrate the ability to return to some previously defined shape or size when subjected to the appropriate thermal procedure. Generally, these materials can be plastically deformed at some relatively low...