Structure, Properties, and Glass Forming Ability of Melt-Spun Fe-Zr-B-Cu Alloys with Different Zr/B Ratios
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INTRODUCTION
DUAL-PHASE Fe-based alloys containing a mixture of amorphous and nanocrystalline phases exhibit a unique combination of soft magnetic properties (high saturation, Curie temperature, permeability, and resistivity and low coercivity), which are superior to the conventional soft magnetic materials. They are generally prepared by the rapid solidification (melt spinning) method to produce an amorphous phase followed by controlled heat treatment to obtain nanocrystalline precipitates in amorphous matrix. Ultra soft magnetic properties arise in these materials due to the combined effect of almost zero magnetocrystalline anisotropy and saturation magnetostriction. According to random anisotropy theory, the exchange coupling between nanocrystalline grains and amorphous matrix results in averaging out of magnetocrystalline anisotropy, which forces the magnetization vector to be aligned parallel to the field direction.[1] The saturation magnetostriction becomes almost zero due to the positive and negative contributions from the amorphous and nanocrystalline phases, respectively.[2] Yoshizawa et al.[3] were the first D. ARVINDHA BABU, Scientist ‘C,’ B. MAJUMDAR, Scientist ‘E,’ and D. AKHTAR, Scientist ‘G,’ are with the Advanced Magnetics Group, Defence Metallurgical Research Laboratory, Hyderabad500058 India. Contact e-mail: bhaskarmajumdar1@rediffmail.com A.P. SRIVASTAVA, Scientific Officer ‘D,’ and D. SRIVASTAVA, Scientific Officer ‘H,’ are with the Materials Science Division, Bhabha Atomic Research Centre, Mumbai-400094, India. B. RAMAKRISHNA RAO, Scientist ‘D,’ is with the Department of Metallurgical and Materials Engineering, Indian Institute of Technology Madras, Chennai-600036, India, and the Naval Materials Research Laboratory, Thane 421506, India. B.S. MURTHY, Professor, is with the Department of Metallurgical and Materials Engineering, Indian Institute of Technology Madras. Manuscript submitted May 31, 2010. Article published online October 22, 2010 508—VOLUME 42A, FEBRUARY 2011
to develop the Fe-Si-B-Nb-Cu (FINEMET) alloy system. Subsequently, Fe-Zr-B-Cu (NANOPERM) alloy containing bcc a-Fe nanograins in the amorphous matrix and Fe-Co-Zr-B-Cu (HITPERM) alloy containing bcc a-FeCo nanograins in the amorphous matrix were developed by Suzuki et al.[4] and McHenry et al.,[5] respectively. A number of investigations were carried out to optimize the structure and soft magnetic properties of the Fe-Zr-B-Cu alloy system with respect to the composition and process parameters. Compositiondependent magnetic properties were investigated using Mo¨ssbauer spectroscopy.[6,7] Kopcewicz et al.[7] carried out a detailed study on the structure and properties of Fe-Zr-B-Cu alloys using a special rf-Mo¨ssbauer technique, which distinguishes magnetically soft nanocrystalline a-Fe particles from the magnetically hard microcrystalline a-Fe particles. Arvindha Babu et al. have recently reported the effect of processing parameters on microstructure and magnetic properties of Fe88Zr7B4Cu1 alloy.[8] The present investigation deals with a stud
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