Shape-memory metallic alloys

Next-generation metallic biomaterials include porous titanium alloys and porous CoCrMo with elastic moduli that more closely mimic that of human bone nickel-titanium alloys with shape-memory properties for dental braces and medical staples rare earth magnets such as the NdFeB family for dental fixatives and titanium alloys or stainless steel coated with hydroxyapatite for improved bioactivity for bone replacement. The corrosion resistance, biocompatibility, and mechanical properties of many of these materials still must be optimized for example, the toxicity and carcinogenic nature of nickel released from NiTi alloys is a concern. ... 

SMP have many advantages compared to metallic shape-memory alloys [4]. SMP are lightweight and allow substantially higher elongations, which are enabling properties for various technical applications. The variation of shuctural parameters of the molecular architecture enabled tailoring of SMP to the demands of specific... 

The example of BaTiOs shows that individual materials which could demonstrate smart behaviour have to exhibit highly nonlinear responses to external stimuli. Besides barium titanate, such a response occurs in metallic shape memory alloys, and in thin layers of a few ceramic compounds such as BiCeOs, TbMnOs or... 

Copper-based metal alloys, 17 847t Copper-based shape-memory alloys,... 

Finally, metallic fibers find some limited applications as reinforcement in composites. They are generally not desirable due to their inherently high densities and because they present difficulties in coupling to the matrix. Nonetheless, tungsten fibers are used in metal-matrix composites, as are steel fibers in cement composites. There is increasing interest in shape memory alloy filaments, such as Ti-Ni (Nitanol) for use in piezoelectric composites. We will discuss shape-memory alloys and nonstructural composites in later chapters of the text. 

Orthodontics - [DENTAL MATERIALS] (Vol 7) -brazing filler metals for [SOLDERS AND BRAZING FILLER METALS] (Vol 22) -shape-memory alloys for [SITAPE-MEMORY ALLOYS] (Vol 21)... 

Shape-Memory Alloys. Stoeckel defines a shape-memory alloy as the ability of some plastically deformed metals (and plastics) to resume their original shape upon heating. This effect has been observed in numerous metal alloys, notably the Ni—Ti and copper-based alloys, where commercial utilization of this effect lias been exploited. (An example is valve springs that respond automatically to change in transmission-fluid temperature.) Copper-based alloy systems also exhibit this effect. These have been Cu-Zn-Al and Cu-Al-Ni systems. In fact, the first thermal actuator to utilize this effect /a greenhouse window opener) uses a Cu—Zn-Al spring. 

Shape-memory materials are those materials that return to a specific shape after being exposed to specific temperatures. In other words, these materials are able to remember their initial shape. This process of changing the shape of the material can be repeated several times. The shape-memory effect has been observed in different materials, such as metallic alloys, ceramics, glasses, polymers and gels. 

Heusler alloys have a rich variety of apphcations, owing to some of their unique properties. Some of these phases are half-metallic ferromagnets, exhibiting semiconductor properties for the majority-spin electrons and normal metallic behavior for the minority-spin electrons. Therefore, the conduction electrons are completely polarized. The Ni2MnGa phase is used as a magnetic shape memory alloy and single crystals of Cu2MnAl are used to produce monochromatic beams of polarized neutrons. 

As one would expect, there are a number of applications that currently use shape-memory alloy materials many more are projected for the future. The earliest application was for greenhouse window openers, with the metal serving as an actuator to provide temperature-sensitive ventilation. Some commercial faucets/showerheads are already equipped with this material that shuts off the water if a certain temperature is reached, which effectively prevents scalding. An intriguing future application will be for automobile frames as we will see later, some plastics may also be designed with shape memory. Someday soon, your car may reshape itself in front of your eyes within minutes after an accident ... 

Explain how shape-memory metals are able to manipulate their shapes in response to temperature fluctuations. Are there other alloy candidates for this type of behavior ... 

In Japan, several commercial projects have been reported in the literature. For example, at the National Research Institute for Metals, the NiTi shape-memory alloy is produced by combustion synthesis from elemental powder for use as wires, tubes, and sheets. The mechanical properties and the shape-memory effect of the wires are similar to those produced conventionally (Kaieda et ai, 1990b). Also, the production of metal-ceramic composite pipes from the centrifugal-thermite process has been reported (Odawara, 1990 see also Section III,C,1). 

From the crude fabrications of the earliest surgical instruments to the highly sophisticated devices of today, materials are the fundamental component of a medical device. Modern devices are usually composed of a metal, plastic, alloy, or various combinations thereof. Improvements in technology have created lighter, stronger materials as well as shape-memory alloys such as nitinol, resulting in major innovations in device design and functionality. 

Shape-memory alloys are a group of metallic materials that can regain their original shape after... 

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