JOURNAL OF MATERIALS SCIENCE LETTERS 17 (1998) 177±180 Nanocrystallization of Fe 85 Zr 6 B 7:5 Cu 1 Al 0:5 amorphous alloy M. AL-HAJ Physics Department, University of Queensland, Brisbane, QLD 4072, Australia E-mail: alhaj@physics.uq.edu.au J. BARRY Centre for Microscopy and Microanalysis, University of Queensland, Brisbane, QLD 4072, Australia Nanocrystalline Fe±Zr±B(±Cu) alloys, prepared by primary crystallization of melt-spun amorphous pre- cursors, are new soft magnetic materials with high saturation magnetization and low coercivity [1]. The microstructure consists of body-centred cubic (b.c.c.) á-Fe nanocrystallites embedded in a residual amor- phous phase. It was reported that both the reduced magnetocrystalline and magnetoelastic anisotropies provide the basis for the magnetic softness of these materials [2]. The addition of 1 at % Cu to Fe±Zr±B alloys was found to reduce the grain size further and to cause the formation of a homogeneous nanocrystalline phase [3]. The crystallization reaction was suggested to be governed by the nucleation-and-grain growth mechanism and the redistribution of Zr and B elements suppresses the grain growth [4]. Studies of the isothermal crystallization kinetics using calorimetric [4, 5] and electrical resistivity [6] measurements revealed that the ®rst-step crystallization process consists only of a single reaction and values between 1 and 2.5 were found for the Avrami parameter. In this letter we report the nanocrystallization process of Fe 85 Zr 6 B 7:5 Cu 1 Al 0:5 (where the composi- tion is given in atomic per cent) amorphous alloy by transmission electron microscopy (TEM), differential thermal analysis (DTA), differential scanning calori- metry (DSC) and thermogravimetric analysis (TGA). The amorphous samples were prepared by the single-roller melt-spinning method. The thickness and width of the resulting ribbons were about 30 ìm and 1.7 mm, respectively. The crystallization reac- tion was followed with a Perkin±Elmer DTA-7 differential thermal analyser at a heating rate of 10 8C min 1 . Isochronal and isothermal crystalliza- tion kinetics were studied with a Perkin±Elmer DSC-7 differential scanning calorimeter under a nitrogen atmosphere. The magnetization measure- ments were carried out with a Perkin±Elmer TGA-7 thermogravimetric analyser at a heating rate of 10 8C min 1 . Samples of the amorphous ribbons were annealed in a conventional furnace under an argon atmosphere. The annealed samples were left to cool slowly to room temperature. The microstructure was observed by a JEM-4010 transmission electron microscope operating at 400 kV. Thin samples for TEM observations were prepared using a liquid- nitrogen cold stage in a Gatan-600 ion-milling machine. X-ray diffraction (XRD) patterns were taken with a Philips D-5000 diffractometer using CuKá radiation. Fig. 1 shows the DTA curve of the as-quenched amorphous sample. Two exothermic peaks, a large peak in the range 460±580 8C followed by a small peak in the range 710±740 8C, are seen in the ®gure, suggesting that a two-step crystallization process had occurred in the amorphous as-quenched sample during heat treatment. In order to clarify these structural changes, TEM observations were done on annealed samples. Fig. 2 shows a high-magni®cation phase contrast image and the selected-area diffraction (SAD) 0261-8028 # 1998 Chapman & Hall Figure 2 A high-magni®cation phase contrast image and the SAD pattern (inset) of the sample annealed for 1 h at 310 8C. The MRO domains are indicated by arrows. 350 450 500 550 600 650 700 750 400 Temperature (°C) -0.65 -0.6 -0.55 -0.5 -0.45 -0.4 -0.35 Temperature change (arbitrary scale) Figure 1 The DTA curve of the as-quenched amorphous alloy. 177