Textures and compressive properties of ferromagnetic shape-memory alloy Ni 48 Mn 25 Ga 22 Co 5 prepared by isothermal fo
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R. Lin Peng The Studsvik Neutron Research Laboratory (NFL), Uppsala University, S-61182 Nyköping, Sweden; and Department of Mechanical Engineering, Linköping University, S-58183 Linköping, Sweden
P. Zetterström The Studsvik Neutron Research Laboratory (NFL), Uppsala University, S-61182 Nyköping, Sweden
Z.F. Zhang Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, People’s Republic of China
X. Zhao and L. Zuo School of Materials and Metallurgy, Northeastern University, Shenyang 110004, People’s Republic of China (Received 24 June 2005; accepted 30 November 2005)
A ferromagnetic shape-memory alloy Ni48Mn25Ga22Co5 was prepared by the induction melting and isothermal forging process. Dynamic recrystallization occurs during the isothermal forging. The deformation texture was studied by the neutron diffraction technique. The main texture components consist of (110)[11¯2] and (001)[100], which suggested that in-plane plastic flow anisotropy should be expected in the as-forged condition. The uniaxial compression fracture strain in the forged alloy reaches over 9.5%. The final room-temperature fracture of the polycrystalline Ni48Mn25Ga22Co5 is controlled mainly by intergranular mode.
I. INTRODUCTION
Ferromagnetic shape-memory alloys (FSMAs) with chemical composition close to stoichiometric Ni2MnGa have attracted much attention during the past few years due to the giant shape memory effect (SME) induced by magnetic fields.1,2 Intensive investigations on this alloy system have already been made regarding many scientific aspects, including crystal structure,3,4 magnetic properties,5 and responses of induced strain to magnetic fields.1,2 The large SME is attributed to the motion of twin boundaries or reselections of martensitic variants under applied magnetic fields. It is well known that the transformation strain and magnetic-field-induced strain are strongly dependent on the orientation of parent austenite and martensitic variants. Thus, explorations on some novel fabrication processes for enhancing preferred grain orientation (crystallographic texture) in the polycrystalline FSMAs do benefit the improvement of their a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2006.0079 J. Mater. Res., Vol. 21, No. 3, Mar 2006
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performance properties. The textured polycrystalline FSMAs can be obtained by using directional solidification, the rapid solidification technique, or plastic deformations. Recent investigations6 show that in spite of the very low ductility at room temperature and the poor formability at elevated temperature, the hot deformation process, a standard procedure used in the fabrications of some structural intermetallic alloys, was successful for preparations of polycrystalline NiMnGa alloys with the modification of microstructures. However, the development of textures has not been studied so far, partly due to the difficulty of measuring t
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