Orientation Dependence of Superelasticity in Ferromagnetic Single Crystals Co49Ni21Ga30
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Dependence of the amount of reversible deformation on the orientation of the crystal axis and testing temperature has been studied using  and [ 124] single crystals of the Co49Ni21Ga30 (at %) alloy upon compression. It has been shown that in the  crystals with T M s (M s is the temperature of the onset of the forward martensitic transformation upon cooling) the reversible deformation is equal to 5.5-6.5% and consists of the deformation connected with the shape-memory effect (SME) equal to 4-4.2%, and of "ferroelastic" deformation equal to 1.5-2.2%, which is reversible upon unloading. The total reversible deformation exceeds the lattice deformation 0 observed upon the B2-L10 martensitic transformation, which is equal to 4.5%. At T > A f (A f is the finish temperature of the reverse martensitic transformation upon heating), the reversible deformation in  crystals is equal to 6.5%. It has been shown electron-microscopically that the reversible deformation equal to 1.5-2.2% in the temperatures range of T = 77-300 K is connected with the development of mechanical twinning in the L10 martensite on (110) L10 planes, which proves to be reversible in the  crystals and can be partly irreversible in the  crystals. Upon heating, the (110) L10 twins of the stabilized L10 martensite pass into the ( 112) B2 twins of the B2 phase. 2010 Pleiades Publishing, Ltd.