EFFECT OF HIGH MAGNETIC FIELD ON CRYSTALORIENTATION,MORPHOLOGY AND MAGNETO-STRICTION OF TbFe 2 AND Tbo.27DYo.7sFe1.s5 ALLOYSDURING HEAT TREATMENT PROCESS

Abstract

The rare–earth giant magnetostrictive materials are one kind of the most important functional materials now. The rare–earth giant magnetostrictive materials of TbFe2 and Tb0.27Dy0.73Fe1.95(R–Fe) alloys were firstly used in sonar system in military. Now, the applications of these two alloys have been developed widely in both industry and civil fields, such as magnetomechanical transducers, actuators, adaptive vibration control systems, and so on. The TbFe2 and Tb0.27Dy0.73Fe1.95 alloys both have the C15–type cubic Laves phase structure, which has strong magnetic anisotropy. This causes that the alloys exhibit different magnetostrictive properties along different crystal orientations. So, the preparation of high orientation degree magnetostrictive materials has a great of importance. In this work, it is predicted that the magnetostricive property of these two alloys can be enhanced with high magnetic field during heat treatment around their Curie and eutectic points. Therefore, a high magnetic field up to 11.5 T was imposed on these two kinds of R–Fe alloys during heat treatment at different temperatures in the experiments. Then the effects of high magnetic field on the crystal orientation, morphology and magnetostriction were analyzed in detail by XRD, metallographic microscope, and static resistance strain gauge. Also, the relationship between structure * K`W}h=dL+ 51006020, 51174056, KPe==osy3H3L+ 2011CB612206 'Jv T= }o9L+ N120409001, N120509001 ^W X: ℄A : 2013–05–28, X` ℄A : 2013–07–24 m8Nb : , ,, 1982 2m, zm DOI: 10.3724/SP.J.1037.2013.00289 9 AE` : KH0[A u TbFe2 ) Tb0.27Dy0.73Fe1.95 ,fl TO / [!)HEj _0^ K 1149 and property is discussed. The results showed that high magnetic field didn’t change the orientation of the R–Fe alloys, but the orientation degree had a great improvement after heat treatment. The phase composition of the two alloys had no change. However, the heat treatment with a magnetic field up to 11.5 T distinctly reduced the rare–earth phase of TbFe2 and obviously increased the magnetic phase. In addition, the magnetostrictive property of TbFe2 alloy increased after the heat treatment with high magnetic field. But for Tb0.27Dy0.73Fe1.95 alloy, the magnetostriction was not obviously enhanced. The reason for the improvement of the magnetostriction is that the Zeeman energy caused by high magnetic field increased the total Gibbs free energy of the system, which made the random orientation in crystals orient along the 〈113〉 direction, and enhanced the magnetostriction of the R–Fe alloys.