Magnetic shape memory alloy
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| More efficient actuators made of 'smart' materials which consume less power |
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Applications being developed for home electronics and autos
Nickel magazine, Mar. 02 -- A nickel-based alloy that changes shape in response to a
magnetic field is attracting interest and funding from some powerful sectors, including the U.S.
military.
Ni2MnGa is a known shape memory alloy that, when distorted, will snap back to its original shape in response
to temperature increases. Recently, the material has been shown to react just as strongly to magnetic
fields.
The ability to control the shape memory effect with magnetism may be a significant leap forward in the development of so-called smart materials. That's because the magnetic response is quicker and more efficient than the traditional temperature-induced response.
Researchers first recognized the potential of the magnetic shape memory effect in Ni2MnGa about a decade ago. A few years later, a significant field-induced strain was observed by a group at the Massachusetts Institute of Technology (MIT) led by Dr. Robert O'Handley and by Dr. Kari Ullakko. In 1996, Ullakko returned to his native Finland, where he started his own company, AdaptaMat, which produces and markets magnetic shape memory (MSM) materials.
Meanwhile, work continued at MIT under the sponsorship of Boeing and other companies. Now the MIT team, as part of a multi-university consortium, has secured long-term funding from the U.S. Department of Defense to develop MSM materials for use in sonar transducers and vibration mitigation systems for the U.S Navy.
So far, the university consortium has been able to boost the strain to 6% at room temperature from about 0.2% at minus 8°C. This has important implications for the material's commercial applications in pumps and valves.
"We found that by changing the composition slightly (to 50% nickel, 29% manganese and 21% gallium) we could get even better results at room temperature," says O'Handley, who is leading the consortium. "We showed that by applying a static stress to the alloy, it could be reset and actuated quasi-statically many times over."
More recent breakthroughs have allowed Dr. O'Handley and his group to demonstrate strain at frequencies of up to 500 hertz and characterize the material's ability to do work (i.e. strain under load). Ni2MnGa has shown 30 times greater strain at room temperature relative to other magnetically controlled materials. The magnetic shape memory effect differs from the classic temperature-induced, or thermoelastic effect. While the latter requires a transformation from the martensite phase to the austenite phase, the former occurs entirely within the martensite phase. The shape changes when twin structures oriented favourably relative to the magnetic field grow at the expense of the other twin structures in the material.
AdaptaMat hopes to take advantage of this unique feature by developing applications that convert magnetic field energy into mechanical motion. These would include simple electromechanical devices that could replace complicated machines in everything from home electronics to automobiles. The company, based in Helsinki, has patented the MSM process in three countries and has applied for patents in several others.
AdaptaMat currently produces MSM sensors as well as actuators capable of stroke lengths of up to 5 millimetres and forces up to 2 kilonewtons. The company expects MSM materials will one day capture a significant share of the annual US$1-billion market for smart materials worldwide.
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Contacts: Emmanouel Pagounis |
