DEVELOPMENT OF FE-BASED SHAPE MEMORY ALLOYS ASSOCIATED WITH FACE-CENTERED CUBIC HEXAGONAL CLOSE-PACKED MARTENSITIC TRANSFORMATIONS .2. TRANSFORMATION BEHAVIOR

As part of a study on the newly developed Fe-based shape memory alloys associated with face-centered cubic-hexagonal close-packed (fcc-hcp) martensitic transformations, transformation behavior is characterized utilizing a combination of electrical resistance, dilatometry, and magnetic susceptibility measurements. The characteristics of thermally induced and strain-induced epsilon-martensitic transformations under the influence of antiferromagnetism are discussed based on the experimental results. The variations of shape memory properties with prestraining temperature are interpreted in terms of the transformation characteristics. It is shown that the epsilon-martensite can be readily strain-induced under the stabilization effect of the antiferromagnetism which strongly suppresses the thermally induced transformation. The strain-induced transformation of epsilon-martensite is more preferred as a predominant deformation mechanism at low temperatures under a combined influence of the antiferromagnetism and other physical factors, whereas the irreversible deformation mode is more likely with prestrain at relatively high temperatures. The transformation characteristics can be significantly changed by alloying and mechanical/thermal treatments. This offers a possibility of developing new practical Fe-based shape memory alloys with a wide range of mechanical and physical properties.