Formation of Large Bulk [(Fe 0.5 Co 0.5 ) 0.75 B 0.20 Si 0.05 ] 96 Nb 4 Glassy Alloy by Flux Melting and Water Quenching
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Formation of Large Bulk [(Fe0.5Co0.5)0.75B0.20Si0.05]96Nb4 Glassy Alloy by Flux Melting and Water Quenching Teruo Bitoh, Akihiro Makino1, Akihisa Inoue1 and A. Lindsay Greer2 Department of Machine Intelligence and System Science, Faculty Systems Science and Technology, Akita Prefectural University, Yurihonjo 015-0055, Japan. 1 Advanced Research Center of Metallic Glasses, Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan. 2 Department of Materials Science and Metallurgy, University of Cambridge, Cambridge CB2 3QZ, UK. ABSTRACT The large bulk glassy [(Fe0.5Co0.5)0.75B0.20Si0.05]96Nb4 alloy specimens with the diameters up to 7.7 mm have been prepared by water quenching the melt immersed in the molten flux of B2O3. The maximum diameter of the obtained specimens is approximately 1.5 times as large as the previous result for copper mold casting should be cooled at the higher rate than that of water quenching. The flux melting improves the glass-forming ability by the elimination of oxides and other inclusion in the molten metal which act as heterogeneous nucleation sites for crystallization.
INTRODUCTION In the last decade, some kinds of (Fe, Co, Ni)-based glassy alloys with a wide supercooled liquid region (∆Tx = crystallization temperature (Tx) − glass transition temperature (Tg)) before crystallization combined with good soft magnetic properties have been found [1–5]. These soft magnetic glassy alloys also exhibit good mechanical properties, e.g., high fracture strength of 3000–5200 MPa [6–9], and are widely noticed as a structural material. However, the glass-forming ability (GFA) of the soft magnetic (Fe, Co, Ni)-based glassy alloys (previously reported values of the maximum diameter of specimens produced actually is 5 mm [3, 8]) is inferior to that of the nonferrous alloys such as Pd-, Zr-, lanthanide-, and Mg-based alloys [1]. Recently, Ponnambalam et al. [11] and Lu et al. [12] reported that the bulk glassy Fe-Cr-Mo-(Y, Dy, Er)-C-B and Fe-Cr(-Co)-Mo-Mn-C-B-Y cylindrical specimens with diameters up to 12 mm can be produced by copper mold casting [10, 11]. However, these alloys are paramagnetic at room temperature. It is well known that the main competition to prepare glassy alloys is attributed to oxides and other inclusion in the molten metal which act as heterogeneous nucleation sites for crystallization. An approach to eliminate the inclusions is to heat and cool the molten metal while it is immersed in molten oxide flux [12, 13]. Up to now, some investigations which apply the flux
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melting technique to Fe-based amorphous or glassy alloys were carried out [14–16], and the cylindrical glassy Fe-(Co, Cr, Mo, Ga, Sb)-P-C-B alloy specimens with diameters up to 4 mm were produced by B2O3 flux melting the mechanically alloyed powders followed by quenching the melt in water [15]. In this study, the application of the flux melting and water quenching technique was investigated to improve GFA of a soft magnetic glassy [(Fe0.5Co0.5)0.75B0.20Si0.05]96Nb4 alloy. Thi
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