Superelasticity and Shape Memory Effects in Polycrystalline Ni-Mn-Ga Microwires
Non-stoichiometric Ni49.9Mn28.6Ga21.5 microwires with a diameter of 30-80 μm and cellular grain size of 1-3 μm were developed by melt-extraction. The superelasticity and shape memory effect of the microwires were investigated on a Dynamic Mechanical Analyzer (DMA Q800). The onset critical stresses for austenite to martensite transformation increase linearly with temperature and can be described by Clausius-Clapeyron relationship. The martensite to austenite transformation occurs upon unloading occurs only at temperatures at least 11 °C higher than the martensite start temperature. The as-extracted microwire was loaded in its martensite state to a strain of 2.7% without breaking and 92% plastic deformation strain recovers upon heating.
Qian, M. F.; Zhang, X. X.; Witherspoon, Cassie; Sun, J. F.; and Müllner, Peter. (2013). "Superelasticity and Shape Memory Effects in Polycrystalline Ni-Mn-Ga Microwires". Journal of Alloys and Compounds, 577(Supplement 1), S296-S299. http://dx.doi.org/10.1016/j.jallcom.2011.10.117