The effect of microstructure on properties and behaviors of annealed Fe 78 B 13 Si 9 amorphous alloy ribbon
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INTRODUCTION
THE dependence of mechanical, relaxation, thermal, and magnetic properties and behaviors of amorphous alloys on annealing has been studied extensively. For example, the sudden increase in coercive field after extensive annealing has been used as an indicator of the onset of crystallization. I~1 On the other hand, the abrupt onset of amorphous alloy embrittlement on annealing has been ascribed to compositional segregation, E2] single-atom considerations, E3] and to the onset of crystallization. Compositional and topological short-range order concepts have been used to account for changes in" amorphous[4]alloyCurie temperature, density, and transport properties. Transmission electron microscopy (TEM) has been used to study the crystallization microstructure of amorphous alloys. However, the location of the microstructure in the sample (surface, interior, etc.) was disregarded.iS] Optical microscopy studies of crystallization in amorphous alloys have shown that alloys of certain compositions tend to start crystallizing at either (or both) of the surfaces while other alloys begin crystallization throughout the bulk. I61 Authors studying amorphous alloys having nominal compositions similar to that of the alloy of the present investigation have used M6ssbauer surface spectroscopy I77 (conversion electron M6ssbauer spectroscopy). This work showed that partial surface crystallization occurs at 710 K (437 ~ after annealing for 36 ks (10 hours). TEM has also been used to report on observations of --0.2/xm surface crystallization platelets.[8] The development of an easy axis perpendicular to the plane of the ribbon in the amorphous samples has been reported. I7'81 M6ssbauer spectroscopy showed that this occurs at an annealing temperature (TA) of 650 K (377 ~ after 36 ks (10 hours). The higher density of the surface-crystallized layer is reported to have caused compressive stresses which give rise to the perpendicular anisotropy observed through magnetostrictive coupling; the magnetic moments in the surface layer still remain coplanar with the ribbon surface due to shape anisotropy. However, the effects of this perpendicular anisotropy on coercivity H. H. LIEBERMANN, R.J. MARTIS, and C. P. WONG are with Allied-Signal Metglas Products, 6 Eastmans Road, Parsippany, NJ 07054. J. MARTI is with Allied-Signal Corporate Technology, Morristown, NJ 07960. Manuscript submitted December 2, 1987. METALLURGICAL TRANSACTIONS A
and hysteresis loop shape could not be observed when this layer is still very thin because bulk anisotropy dominates. When the thickness of the crystallized layer increases further (->-5/xm[9]), domain wall pinning becomes significant and the hysteresis loop becomes sheared while coercivity increases very abruptly. A manifold approach to characterize the crystallization of Fe78BI3Si9 amorphous alloy on annealing was taken in the present investigation. Magnetic measurements were used to monitor changes in the coercive field, resulting from stress relaxation and from crystallization, through domain wa
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