L Journal of Alloys and Compounds 317–318 (2001) 423–427 www.elsevier.com / locate / jallcom Low temperature formation of nanocrystalline Fe–W and Fe–Mo compounds a, a b b b * A.A. Novakova , T.Yu. Kiseleva ,V.V. Lyovina , D.V. Kuznetsov , A.L. Dzidziguri a Moscow M. V . Lomonosov State University, Department of Physics, 117234 Moscow, Russia b Moscow State Steel and Alloys Institute, 117936 Moscow, Russia Abstract Nanocrystalline Fe–W and Fe–Mo compounds obtained by coupled reduction of fine dispersed FeOOH with H WO (or with 2 4 ¨ H MoO ) in continuous H flow at the temperature range 700–7408C were studied by means of Mossbauer spectroscopy and X-ray 2 4 2 diffraction. The formation of partially disordered and even amorphous intermetallic phases and solid solutions with extended concentrations was observed. Hydrogen incorporation in the structure of disordered intermetallic phases during the reduction process was revealed.  2001 Elsevier Science B.V. All rights reserved. ¨ Keywords: Nanocrystalline compounds; Intermetallic and amorphous phases; Mossbauer spectroscopy 1. Introduction 2. Experimental Comparative structural analysis of nanocrystalline com- Chemically dispersed nanocrystalline Fe–W and Fe–Mo pounds Fe–W and Fe–Mo prepared by the same method: compounds with different W (or Mo) concentrations were coupled reduction of dispersed oxygen containing com- obtained by means of a coupled reduction of fine dispersed pounds in continuous H flow at the temperature range FeOOH and H WO (or H MoO ) in continuous H flow 2 2 4 2 4 2 700–7408C is interesting for the understanding of low at the temperature range 700–7408C [6,7]. ¨ temperature alloying processes. The equilibrium phase X-ray diffraction (XRD) and Mossbauer spectroscopy diagrams of these two systems are very similar. They have (MS) were used for the structural characteristics study of very narrow (near 1%) regions of b.c.c. solid solutions Fe the samples (grain size, phase composition, concentrations and W (or Mo) for both end members and several of diluted elements in solid solutions). XRD was per- intermetallic compounds. Among them l-Fe W (or Fe Mo) formed at Rigaku-DX / Max u –2 u diffractometer with Cu 2 2 ¨ and m-Fe W (or Fe Mo ) are stable at room temperature. Ka radiation. The Mossbauer spectra were obtained at 7 6 7 6 The interfacial enthalpies in kJ per mole for solved W (or room temperature using constant acceleration spectrometer 57 Mo) in Fe [1] estimated by Miedema are small and with Co (Rh) source. The spectra were fitted by means of different: DH50 for Fe–W and DH527 for Fe–Mo. But the UNIVEM and MSTools programs. As usual, all the for both Fe–W and Fe–Mo nanocrystalline powder com- isomer shift values are given with respect to metallic Fe at pounds obtained by ball milling or by vapour quenching room temperature. the different concentration ranges of amorphous phases formation were established experimentally [2–5]. The purpose of the present paper is to analyse the 3. Results and discussion nonequilibrium phase formation process during the cou- pled reduction in Fe–W and Fe–Mo by means of X-ray XRD patterns of the Fe–W nanocrystalline compositions ¨ diffraction and Mossbauer spectroscopy. with W concentrations of 9–55 at% are shown in Fig. 1. Judging from the picture, besides the peaks from b.c.c. crystalline solid solutions Fe and W, a diffusive halo *Corresponding author. o E-mail address: aan@runar.phys.msu.su (A.A. Novakova). appears in the range of angles 35–50 . This halo is most 0925-8388 / 01 / $ – see front matter  2001 Elsevier Science B.V. All rights reserved. PII: S0925-8388(00)01420-1