Crystallization of Co 100-x Pt x B 10 Si 12 amorphous metallic alloys
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5/24/04
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Crystallization of Co100-xPtxB10Si12 Amorphous Metallic Alloys CHUNG-SIK YOO, SUNG K. LIM, C.S. YOON, and C.K. KIM Alloys of Co78-xPtxB10Si12 were produced using the melt-spin process in order to study the crystallization behavior and ensuing magnetic properties of the Co-Pt amorphous alloys as a function of the Pt content. We showed that when x 15, well below its stoichiometric composition, CoPt intermetallic compound crystallized in the amorphous alloy. Below this composition, the main crystallization product was Co with Pt dissolved in its lattice. The nucleation of CoPt greatly altered the crystallized microstructures and magnetic properties of the Co-Pt amorphous alloys during annealing. In spite of the nucleation of CoPt with its high magnetic anisotropy, the highest coercivity was obtained when x was 15, free of the CoPt grains. It was also concluded that the Pt addition, in general, triggered crystallization to occur at a progressively lower temperature.
I. INTRODUCTION
IN the past decade, transition metal-metalloid amorphous magnetic alloys containing Fe, Ni, and Co have been intensively studied due to their soft magnetic properties ranging from low coercivities and hysteresis loss to high permeabilities, which render the alloys to be outstanding candidates for a host of applications including electronics, magnetic recording heads, magnetic sensors, and large transformers.[1] Most of all, material properties of these amorphous alloys were found to be sensitive to both the composition and processing history, providing opportunities to tailor the magnetic and engineering properties of the material as desired. In addition to the practical applications, studying the amorphous alloy system provides important information on metastable glass structures and crystallization kinetics as well as ensuing magnetic properties dictated by the microstructual evolution during crystallization. We have previously studied the crystallization of Co-based metallic glasses alloyed with different elements (Fe and Cr) and found that both the crystallization and the resulting magnetic properties critically depended on the alloying element type as well as on the concentration of the alloying element.[2,3,4] In this study, Co78-xPtxB10Si12 amorphous alloys were produced in order to study the effects of the Pt addition on the crystallization and magnetic properties. Although Co and Pt form a complete solid solution, the Pt addition slightly suppresses the liquidus temperature of the alloy near the Co-rich end of the phase diagram.[5] Although other factors such as kinetics and the nucleation rate of the primary phase can affect the glassforming ability, the phase diagram suggests that we should be able to form the Co-Pt metallic glasses. Meanwhile, both the relatively large atomic size of Pt and its ability to form an intermetallic compound are expected to substantially alter the annealed microstructure and the resulting magnetic properties. Moreover, the Co-Pt alloy system has recently received much att
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