FORMATION OF SIGMA-LIKE Mo-RICH TERNARY PHASE IN Fe 40 Ni 38 Mo 4 B 18 GLASS FORMING ALLOY T.A.M. Aboki, S. Baudu, L. Robbiola and P. Ochin * Laboratoire de Me ´tallurgie Structurale E.N.S.C.P., 11, rue Pierre et Marie Curie, F 75231 Paris Cedex 05 France * C.E.C.M/C.N.R.S., 15, rue Georges Urbain, F 94407 Vitry-sur-Seine Cedex, France (Received February 9, 2000) (Accepted in revised form April 13, 2000) Keywords: EDS; Intermetallic; Iron; Nickel; Molybdenum Introduction Fe-B alloys are glass forming alloys intensively studied for their good mechanical and magnetic properties [1,2,3,4,5,6]. Among the wide range of Fe-based alloys with other transition element [7,8], FeNiMoB alloys show higher atomic packing revealed by their slightly higher density, about 7.9 g/cm 3 [9]. Previous studies [8,10,11] have demonstrated that under heating, the structural relaxation of the amorphous structure for Fe 40 Ni 38 Mo 4 B 18 alloy is more progressive than for Fe 79 B 13 Si 9 and Fe 81 B 13.5 Si 3.5 C 2 . The free volume vanishes abruptly in the two late whereas it is redistributed in the first alloy. In addition, the whole atomic reorganisation during the structural relaxation leads to complex crystallisation system giving numerous crystalline Fe-based phases. This primary crystallisation feature and the higher density indicate the Fe 40 Ni 38 Mo 4 B 18 composition as possible candidate for bulk amorphous alloys preparations. Starting bulk amorphous alloys preparation study with this composition, we obtained crystalline material with ternary-intermetallic-sigma precipitates, a close-packed structure. The sigma phase has been characterised by scanning electron microscopy (SEM) observations, energy dispersive x-ray spectrometry (EDS) analysis, x-rays diffraction (XRD) determinations and transmission electron microscopy (TEM) selected area diffraction (SAD) patterns. Experimental The quaternary Fe-Ni-Mo-B alloy have been prepared from good purity components: Fe99,99%(from melting zone), Ni99,7%(Carbonyl remelted under helium), B99%, Mo99,95. Pre-alloying of the components, previously carefully cleaned and weighted in the right proportions, was carried out by induction melting in a water-cooled copper crucible. A second induction-melting in electromagnetic levitation has been performed, with an overheating more than one hundred degrees above the liquidus temperature in order to ensure a perfect chemical homogeneity of the melt and optimise the alloy glass forming ability (GFA) [12]. Two different copper moulds have been used to cast the melt at around 100K/s giving two shaped- ingots. A parallelepiped (P) ingot of 4 mm thick, 20 mm width and 50 mm length and a cylindrical (C) ingot of 8 mm of diameter, 50 mm of length. The investigated samples have been cut following ingots cross-section and length. Scripta mater. 43 (2000) 453– 458 www.elsevier.com/locate/scriptamat 1359-6462/00/$–see front matter. © 2000 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All rights reserved. PII: S1359-6462(00)00426-7