New Magnetic Metallic Glasses with Reduced Metalloid Content
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B.H.
Kear,
B.C.
Giessen,
and M. Cohen,
editors
217
NEW MAGNETIC METALLIC GLASSES WITH REDUCED METALLOID CONTENT R. C. O'HANDLEY AND N. J. GRANT MIT, Cambridge, MA 02139 ABSTRACT Several new magnetic amorphous alloys containing early transition metals (TE) and having reduced metalloid (M) content have been melt spun. Some properties of three examples of this new class, 1) Co80 Nb1 4, B, 2) Co Nb 10 B 6, and 3) Fe 8 1 Nb B1 4, are presented. The dominant X'te transition meKa1 (TL) content assures an appreciable magnetic moment while the presence of an early transition metal significantly enhances the stability against crystallization. Crystallization temperatures are 1) 742K, 2) 698K, and 3) 762K for the three alloys, respectively. X-ray diffraction patterns show the materials to be amorphous and to exhibit a large-r correlation length (approximately 2.0 A) that is shorter than is typiclly observed in TL8 yM %2 glasses containing more than one transition meta) s ecies (approximately 2.3 - 2.5A). The coercivities of the glassy compositions range from 30 to 70 mOe.
INTRODUCTION Several new amorphous metallic alloys based on approximately 80 to 84 at% cobalt or iron and stabilized with up to 14 at% boron and up to 14 at%niobium have been melt spun. Most notable are 1) Co Nb B , 2) Co8 Nb10 B6 , and 3) Fe 8 1 Nb B1 4'. The addition to the late Grasi~ion merta (1• )base of both an eatly transition metal (TE) species and a metalloid (M), at concentrations lower than in the typical TLQoM 0 glasses, accomplishes three objectives. First, it leads to alloyg which wed the strong ferromagnetic character of the TL 0 M2 ^ glasses with the high thermal stability of early/late-transition me a2 ?TE 4TL 0 ) alloys. Second, it reduces the depressing effect of the me~al•ids on the TL magnetic moments. (This is often replaced by a strong depression due to the TE species.) Third, it allows for the fabrication of glassy alloys which crystallize to a larger fraction of ductile phase. This is of importance in developing useful and interesting microcrystalline alloys. The cobalt-base alloys fabricated for this program represent a new class of amorphous materials whose compositions are notglinear combinations of known TL-M and equiatomic TE-TL amorphous alloys [1]. (Such linear combinations would fall between the dashed lines in Fig. 1. The Fe-base composition is not so clearly outside this region.) The new Co-base compositions may, however, be thought of as TE-TL glasses of the type TL ZrI0 TL = Fe, Co, or Ni [23 to which boron has been added to enhance glass formation and stability. Our preliminary results suggest that the structures of these new alloys are in fact more like TE 0TL1 0 glasses plus metalloid than they are like TL 8MN plus TE TL_ 9 0 glasses. However, a resolution of this question rquires more th roug investigation.
218 GLASS FABRICATION Binary phase diagrams showing attractive eutectics suggest candidate systems = 1633K at 11.5 = 1508K at 14.5 at% Nb), Fe-Nb (T for study: Co-Nb (T at% Nb) , Co-Ti (T eu 1403Kat 21 at
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