Development of Ferromagnetic Shape Memory Alloys by Rapid Solidification Route

Abstract

The ongoing drive to innovations has led to an array of highly adaptive structures called "Smart Materials". Shape memory actuators based on Nitinol (NiTi alloys)and others comprised of thermal mode of actuation between marten-sitic and austenitic state during heating and cooling cycles which yield to slower response times. Such applic-ation constraints led to the development of Ferromagnetic Shape Memory Alloys (FSMAs) that undergo magnetic field induced reversible martensite to austenite transformation through rearrangement of the martensite variants bringing about an overall change of shape. The faster mode of actuation through magnetic field has opened the scope of these alloys in highly potential areas like aircrafts (active flow controls), biomedicals (micro-pumps) and robotics(latches, valves etc). For such magnetic micro-electro-mechanical systems (MagMEMS), NiMnGa alloys were the first known materials. These materials are convent-ionally prepared by crystal growth tehcniques that are not only prone to defecs, expensive and also time consuming. Hence, the need for an easier and less expensive method of processing techniques led to some recent consuming. Hence, the need for an easier and less expensive method of proc-essing techniques led to some recent investigations on the use of rapid solidification technique by melt spinning for the preparation of FSMAs in the form of ribbons. The effort was to obtain a disordered state far away from equilibrium stoichiometry which can modify transformation behaviour and thermomechanical characteristics.