Mechanical Properties and Crystallization Behaviors of Microstructured Co-Fe-P Amorphous Alloys
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NTRODUCTION
AMORPHOUS alloys or metallic glasses have attracted considerable attention because of their exceptional mechanical, chemical, and magnetic behaviors in the applications in many fields.[1,2] For the fabrication of amorphous alloys, there are conventional methods such as casting, melt spinning, and sputtering.[3–5] Due to the intrinsic glass forming ability of alloys, there is a necessity of high cooling rates for the formation of an amorphous phase. Hence, the size and shape of these amorphous alloys are limited and their applications in broader fields have been restricted.[6] Even for the recently developed bulk metallic glass, the diameter is typically smaller than 1 cm. It is most desirable that the size of metallic glasses can be increased to meet the needs in some demanding applications. For example, it is desirable that soft-ferromagnetic metallic glasses used as transformer cores would have large sizes, i.e., with their dimensions much larger than 1 cm. Soft ferromagnetic Fe-based or (Fe, Co)-based amorphous alloys have been used in electronic and electrical devices for many years. For examples, Fe-Si-B and Co-Fe-Si-B are classical soft ferromagnetic amorphous alloys, which have been used as high saturated magnetization-type and high-permeability-type electrical devices, respectively.[2] Large Fe-based and (Fe, Co)-based alloys are usually synthesized by the consolidation methods. Stoica et al. prepared Fe77Al2.14Ga0.86P8.4C5B4Si2.6 powders from melt-spun ribbons by high-energy ball milling and subsequently compacted the resulting powders in the supercooled liquid region.[7] Shen et al.[8] and Ishihara et al.[9] synthesized amorphous YING SHEN, Postgraduate Student, and GUANG-PING ZHENG, Professor, are with the Department of Mechanical Engineering, Hong Kong Polytechnic University, Hong Kong, P.R. China. Contact e-mail: [email protected] XIU-CHENG ZHENG, Associate Professor, is with the Department of Chemistry, Zhengzhou University, Zhengzhou 450001, P.R. China. Manuscript submitted May 26, 2010. Article published online October 19, 2010 METALLURGICAL AND MATERIALS TRANSACTIONS A
Fe65Co10Ga5P12C4B4 and Fe67Co9.5Nd3Dy0.5B20 alloys by spark plasma sintering. In their microstructures, the Fe-based and (Fe, Co)-based alloys synthesized by such consolidation methods[7–9] and polycrystalline alloys are very similar. The only difference is that the former has noncrystalline grains. It is thus expected that the microstructures of the amorphous alloy significantly affect its mechanical and magnetic properties, but the effects have not been well characterized to date. On the other hand, there are some unsatisfactory magnetic and mechanical properties of those amorphous alloys synthesized by consolidation methods. For example, the ball milling induced internal stresses in the amorphous powders are very large and result in an increase of magnetic coercivity of the amorphous alloys; crystallization may occur during consolidation under high pressure in the supercooled liquid state and would cause dramatic change o
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