Crystallization in Fe- and Co-Based Amorphous Alloys Studied by In-Situ X-Ray Diffraction
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ODUCTION
THE Fe- and Co-based amorphous alloys have attracted great attention because of their high glass-forming ability and good mechanical and magnetic properties.[1] In a weak magnetic field, they all have a speedy response and high stabilization[2] and can be used in electrodynamic potential generators to reduce jitter due to large Barkhausen and Matteucci effects.[3] The Fe- and Co-based amorphous alloys exhibit good soft magnetic properties.[1,4] For example, Fe-based amorphous alloys with high saturation magnetization up to 1.7 T, low coercive force of 3.3 to 6.2 A/m, and high effective permeability of 8300 to 15,000 were synthesized in the Fe-B-Si-P alloy system.[5] The upper strength limit of glassy alloys was significantly increased to over 4000 MPa for Fe- and Co-based bulk glassy alloys, which can be used as a new type of ultrahigh strength material.[6] With these excellent properties, Fe- and Co-based amorphous alloys can be used in different types of sensors. However, the low thermal stability of amorphous alloys has prevented a further extension of application fields. When crystallization occurs, many merits of amorphous alloys are lost.[7] This trend requires a sufficient understanding of crystallization kinetics of amorphous alloys in order to define suitable processing parameters that will yield
L.J. ZHANG, P.F. YU, and H. CHENG, Ph.D. Candidates, and M.D. ZHANG, D.J. LIU, and Z. ZHOU, Master Students, and Q. JIN and R.P. LIU, Professors, are with the State Key Laboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao 066004, China. P.K. LIAW, Professor, is with the Department of Materials Science and Engineering, The University of Tennessee, Knoxville, TN 37996. G. LI, Professor, is with the State Key Laboratory of Metastable Materials Science and Technology, Yanshan University, and also with the Department of Materials Science and Engineering, The University of Tennessee. Contact email: [email protected], [email protected] and [email protected] Manuscript submitted December 29, 2015. METALLURGICAL AND MATERIALS TRANSACTIONS A
desirable microstructures and favorable properties.[8] X-ray diffraction (XRD) is one of the most direct methods to study phase transformations. The use of the in-situ X-ray opens the possibility for time-resolved kinetic studies. In this article, the crystallization-activation energy and Avrami exponent, n, are calculated, and the crystallization mechanisms of the three amorphous alloys are analyzed.
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EXPERIMENTAL
The master alloy ingots were prepared by melting a mixture of 99.99 pct (with purity) pure elements in an argon atmosphere. Rapidly solidified amorphous ribbons of Fe80Si20, Fe78Si9B13, and Fe4Co67Mo1.5Si16.5B11 (in at. pct) with a cross section of 0.02 9 1.6 mm2 were prepared in a pure argon atmosphere by the melt-spinning technique. The amorphous nature of ribbon samples was ascertained with XRD measurements processed by a Siemens D5000X diffractometer with the Cu Ka radiation. The sample was heated in situ by means of a furnace attache
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