Core Losses and Soft Magnetic Properties of Nanocrystalline Fe-Zr-Nb-B Alloys with Zero-Magnetostriction
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Core Losses and Soft Magnetic Properties of Nanocrystalline Fe-Zr-Nb-B Alloys with Zero-Magnetostriction Akihiro Makino, Akihisa Inoue 1 and Tuyoshi Masumoto 2 Department of Machine Intelligence and Systems Science, Faculty Systems Science and Technology, Akita Prefectural University, Honjo 015-0055, Japan. 1 Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan. 2 The Research Institute of Electrical and Magnetic Materials, Sendai 980-0807, Japan.
ABSTRACT The structure, the soft magnetic properties and the core losses for Fe-Zr-Nb-B(-Cu) nanocrystalline alloys were investigated. It has been already reported that the typical ternary nanocrystalline Fe90Zr7B3 and Fe84Nb7B9 alloys exhibit good soft magnetic properties and a small negative and a small positive magnetostriction (λs), respectively. The soft magnetic properties of the nanocrystalline Fe84–90(Zr, Nb)7B3–9 quaternary alloys with mixed compositions of Fe90Zr7B3 and Fe84Nb7B9 cannot be improved whereas very small magnetostrictions are obtained. The quaternary alloys with 7 at% (Zr + Nb) have structures of an amorphous with α-Fe phases on the free and roll-contacted surfaces at an as-quenched state. The crystalline surface layers deteriorate the soft magnetic properties at a crystallized state. The high saturation magnetic induction of 1.64 T, the high permeability of 60,000 at 1 kHz and the very low core loss of 0.9 W/kg at 1.4 T and 50 Hz are obtained for the Fe85.5(Zr1/3Nb2/3)6B8.5 alloy containing 6 at% of (Zr + Nb) content with nearly zero-λs produced by crystallizing the single amorphous phase without the crystalline surface layers. The thermal stability of the core loss of the quaternary alloy is significantly higher than that of the Fe78Si9B13 amorphous alloy. The crystalline surface layers of the Fe84–90(Zr, Nb)7B3–9 quaternary alloys disappear by 1 at% Cu addition, which results in significant improvement of the soft magnetic properties at a crystallized state. INTRODUCTION In the last decade, some nanocrystalline soft magnetic alloys consisting of bcc nanoscale crystalline phase have been obtained by crystallizing melt-spun amorphous ribbons. The alloys are classified into two groups. One is composed of Fe-metalloid amorphous based alloys such as Fe-Si-B-Nb-Cu [1, 2] containing the elements immiscible with Fe such as Cu. These alloys exhibit good soft magnetic properties, however, their saturation magnetic induction (Bs) (up to L7.1.1
Table I. Grain size (D), saturation magnetic induction (Bs), permeability (µe), coercively (Hc), magnetostriction (λs) and core loss (W) of nanocrystalline ternary Fe-M-B alloys. D
Bs
(nm)
(T)
Fe90Zr7B3
13
1.70
Fe84Nb7B9
9
1.52
µe*
Hc
λs -6
W **
(A/m)
(10 )
(W/kg)
30,000
5.8
-1.1
0.21
51,000
4.8
+0.6
0.14
* 1 kHz, 0.4 A/m ** 50 Hz, 1.4 T
1.4 T) is lower than the Fe-metalloid amorphous alloys mainly because of the decrease in Fe concentration by the addition of Nb and Cu. Therefore the development of a new soft magnetic alloy with high Bs above 1.5 T has strongly been
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