240_l19_demos - Memory Metals, 2 Memory metals are...

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Memory Metals Nitinol, which is a nickel-titanium allow, is often referred to as a “memory metal” or a “smart material” due to its ability to “remember” arrangements of atoms at different temperatures, and to retain the bulk shape of a material (other examples include Au-Cd, Cu-Al-Ni, Cu-Zn-Al and Fe-Mn-Si alloys). Nitinol has almost equal numbers of Ni and Ti atoms, and phase change temperature can be tuned by slightly varying this ratio. High-temperature phase: austenite , cubic symmetry, rigid Low-temperature phase: martensite , less symmetric, elastic The 24 ways of producing martensite from austenite results from the cubic structure having 6 identical face diagonal planes, each of which can shift in one of two directions and can distort (shear) in one of two directions, 6 x 2 x 2 = 24.
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Unformatted text preview: Memory Metals, 2 Memory metals are superelastic at certain temperatures, and are used in a variety of applications, due to their ability to return to the initial configuration: Eyeglass frames Deicing systems Coffee pot thermostats Electrical connectors Clamps Sculptures NiTi alloys are also biocompatible , allowing them for use in: vascular stents, anchors for attaching tendons to bone, medical guidewires (e.g., braces), medical guidepins, root canal files, bendable surgical tools, and devices for closing holes in the heart. NASA and the aeronautics industry currently use the shape memory of NiTi alloys to deploy solar arrays and antennae on satellites, and to control the balance on helicopter rotor blades. Phase Diagram of NiTi Phase Diagram of Brass (CuZn)...
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240_l19_demos - Memory Metals, 2 Memory metals are...

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