Science and Technology of Shape-Memory Alloys: New Developments
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Science and
Technology of Shape-Memory Alloys: New Developments
Kazuhiro Otsuka and Tomoyuki Kakeshita, Guest Editors Abstract The martensitic (also called displacive or diffusionless) transformation is a classical cooperative phenomenon in solids similar to ferromagnetism. Although the displacement of each atom is not large, the transformation results in a macroscopic change in shape, since all of the atoms move in the same direction in a domain or variant. As a result, unique properties arise, such as the shape-memory effect and superelasticity, whose characteristics are quite distinct from those of normal metals and alloys. Because of these unique properties, shape-memory alloys (SMAs) have been used as new functional materials for applications such as couplings, sensors, actuators, and antennas for cellular phones. In this issue of MRS Bulletin, we present an overview of recent progress in this field. In this introductory article, we discuss fundamental notions, such as the mechanism of the shape-memory effect, the martensitic transformation, and superelasticity, along with examples of applications and other important recent topics not treated in the following articles. It will be shown that progress in the science and technology of shape-memory alloys has been achieved by the side-by-side development of fundamentals and applications. Keywords: alloys, crystal, mechanical properties, shape memory.
Why Are Shape-Memory Alloys Interesting and Important Now? The martensitic (also called displacive or diffusionless) transformation is a classical cooperative phenomenon in solids similar to ferromagnetism. Although the displacement of each atom is not large, the transformation results in a macroscopic change in shape, since all of the atoms move in the same direction in a domain or variant. As a result, unique properties arise, such as the shape-memory effect and superelasticity, whose characteristics are quite distinct from those of normal metals and alloys. Because of these unique properties, shapememory alloys (SMAs) have been used as new functional materials for applications
MRS BULLETIN/FEBRUARY 2002
such as couplings, sensors, actuators, and antennas for cellular phones. Although the shape-memory effect was first discovered in a Au-Cd alloy in 1951,1 research became much more active after the effect was found in a Ti-Ni alloy in 1963.2 Recently, SMAs have been attracting keen attention as smart materials, since they can function as sensors and actuators simultaneously. The transformation itself is also quite interesting, since it is a typical cooperative phenomenon that includes various unsolved or overlooked problems. Thus, research on SMAs is becoming a target of physicists as well as materials scientists and
engineers, and martensitic transformations are being studied by various approaches, both experimental and theoretical. For these reasons, rapid progress has been made recently in both fundamentals and applications, and the purpose of this issue is to present the important results. The discussions w
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