I didn't find any Cu based SMA's as actuators in real time applications?why?
is there any reason?
Solubility of Ni in Cu is easier to understand and ductility is better when compared to iron based SMA. Thermo-mechanical properties are much better. In addition, practically transformation is easier and much stable with Cu based SMA.
Besides many other reasons, basically, Cu based martensites are meta-stable phases prone to aging and precipitationf(formation) of equilubrium phases (which do not contribute to SME any more) during heating cycles, as can be seen understood from the phase diagrams of Cu-based SMAs. So their cooling - heating cycle life is limited to few hundreds and due to compositional variations during precipitation their properties vary with cycle. They may be used for single cycle applications, such as fire alert components or non-critical applications. On the other hand TiNi alloys can endure millions of cycles if their compositions are adjusted (by an initial ppt. heat treatment for example) to a saturated value ( see the range of solubility of beta from the Ti-Ni phase diagram).
Hope this helps.
Regards.
thank u very much for your reply sir. in the literature survey i read that many techniques are introduced to change the martensite stabilization in copper based shape memory alloys. really does this method works for utilising this SMAs as actuators .
The thermomechanical behaviour of Cu-based SMA. e.g. lower electrical resistivity = slower heating.
http://www.sciencedirect.com/science/article/pii/S0261306913011345
it is not easy , These alloys are the second best choise bcause it is not easy to machine (EDM,Wire cutting ) they do have a small range, but if it modified it can give more range ,but above all it is a economical subsiute for the Ni-Ti Alloys when it is not cost effective
Unlike Ni-Ti SMAs those based on copper are prone for what is known as stabilization of martensite, leading to an increase in the As and Af temperatures. Moreover, aging leads to precipitation some second phases, which hinder the movement of martensite/austenite interfaces during the reverse transformation. In addition, the recovery strain and recovery stress are minimal.
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