Influence of Melt-Spinning Parameters on the Structure and Soft Magnetic Properties of (Fe 0.65 Co 0.35 ) 88 Zr 7 B 4 Cu
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NANOCRYSTALLINE soft magnetic materials (FINEMET, NANOPERM, and HITPERM), obtained through partial devitrification of amorphous precursor, have been studied extensively because of their superior properties as compared to the conventional soft magnetic alloys. FINEMET (Fe-Si-B-Nb-Cu) alloys, developed by Yoshizawa et al.,[1] and NANOPERM (Fe-Zr-B-Cu) alloys, developed by Suzuki et al.,[2] exhibit very low coercivity (Hc), high permeability (l), and low losses, which can be used for room-temperature applications such as distribution transformers and sensors. On the other hand, HITPERM (Fe-Co-Zr-B-Cu) alloy, developed by McHenry et al.,[3] possesses higher saturation magnetization (4pMs) and Curie temperature (Tc) and can be used for high-temperature applications such as the rotor assembly of an aircraft integrated power unit, which operates at 773 to 873 K (500 to 600 C).[4] The alloy has been developed by partial substitution of Fe by Co in NANOPERM alloy, which leads to enhancement of saturation magnetization and Curie temperature at the cost of coercivity and permeability.
D. ARVINDHA BABU, Scientist ‘‘C,’’ B. MAJUMDAR, Scientist ‘‘E,’’ and D. AKHTAR, Scientist ‘‘G,’’ are with the Defence Metallurgical Research Laboratory, Hyderabad-500058, 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. Manuscript submitted June 22, 2009. Article published online February 12, 2010 METALLURGICAL AND MATERIALS TRANSACTIONS A
Numerous investigations have been carried out to study the effect of composition, alloying addition, heat treatment, etc. on the structure and soft magnetic properties of Fe-Co-Zr-B-Cu alloy systems.[5–9] Willard et al.[5] have investigated the sequence of reaction during annealing treatment of Fe-Co-Zr-B-Cu alloys and reported that a ¢-FeCo (B2) nanocrystalline phase is precipitated on crystallization. Mu¨ller et al.[9] reported, at higher Co content, fcc Co phase precipitates along with a-Fe(Co) phase in Fe86–xCoxZr7B6Cu1 alloys. The Tc of the amorphous phase was also found to increase with Co content, and beyond 20 at. pct Co, it is higher than the crystallization temperature of a-Fe(Co) phase resulting in difficulties of measuring Tc. Johnson et al.[10] have studied the effect of changing the ratio of Fe:Co from 50:50 to 65:35 on the magnetic properties of (FeCo)89Zr7B4 alloys. The alloy of 65:35 was found to possess higher permeability than the alloy of 50:50 because of high saturation magnetization. Effect of process parameters during melt spinning on the structure and soft magnetic properties of nanocrystalline materials have been studied in Fe-Si-B-Cu-Nb[11] and Fe-Zr-Nb-B-Cu[12,13] alloys. In the case of Fe-Si-BCu-Nb alloys, Shahri et al.[11] reported that lower wheel speed leads to the deterioration of soft magnetic properties due to the decrease in degree of amorphicity and increase in magnetostriction. In the case o
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