Physical metallurgy of Ti–Ni-based shape memory alloys

Recent developments in the research of shape memory alloys

Shape memory properties provide a very attractive insight into materials science, opening unexplored horizons and giving access to unconventional functions in every material class (metals, polymers, and ceramics). In this regard, the biomedical field, forever in search of materials that display unconventional properties able to satisfy the severe specifications required by their implantation, is now showing great interest in shape memory materials, whose mechanical properties make them extremely attractive for many biomedical applications. However, their biocompatibility, particularly for long-term and permanent applications, has not yet been fully established and is therefore the object of controversy. On the other hand, shape memory polymers (SMPs) show promise, although thus far, their biomedical applications have been limited to the exploration. This paper will first review the most common biomedical applications of shape memory alloys and SMPs and address their critical biocompatibility concerns. Finally, some engineering implications of their use as biomaterials will be examined.

Shape Memory Materials for Biomedical Applications

Etude de l'influence de la teneur en cuivre (5, 7.5, 10, 12.5, 15, 20at%) sur les caracteristiques de memoire de forme (temperatures de transformation, allongement, hysteresis) des alliages Ti 50 Ni 50-x Cu x .

Cu-Content Dependence of Shape Memory Characteristics in Ti–Ni–Cu Alloys

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.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0883769400020194

Y Kudoh

Papers

CRYSTAL STRUCTURE OF THE MARTENSITE IN Ti-49.2 at.%Ni ALLOY ANALYZED BY THE SINGLE CRYSTAL X-RAY DIFFRACTION METHOD