JOURNAL OF MATERIALS SCIENCE LETTERS 17 (1998) 1125±1127 Nanocrystallization kinetics of Fe 85:5 Zr 4 Nb 4 B 5:5 Al 1 amorphous alloy MANSOUR AL-HAJ,  J. BARRY {  Physics Department, { Centre for Microscopy and Microanalysis, University of Queensland, Brisbane, QLD 4072, Australia Fe 86 Zr 4 Nb 3 B 6 Cu 1 nanocrystalline alloy is a new good soft magnetic material with high permeability and low coercivity [1]. Upon annealing, the as- quenched amorphous phase crystallizes in a two- stage crystallization process in which a single b.c.c. á-Fe nanocrystalline phase appears after the ®rst stage, and coarse á-Fe grains plus intermetallic phases appear after the second stage. Our previous study of the crystallization behavior of Fe 85:5 Zr 4 Nb 4 B 5:5 Al 1 amorphous alloy [2], which was obtained by the replacement of the 1 at % Cu in Fe 86 Zr 4 Nb 3 B 6 Cu 1 alloy by 1 at % Al and 0.5 at % Fe plus 0.5 at % B by 1 at % Nb, revealed that the second stage of crystallization in this alloy system involves only the formation of intermetallic phases without any increase in the grain size of the nanocrystalline phase. We suggested this was due to the enhanced sharp concentration gradients of both Zr and Nb which prevented the grain growth at the second stage. In this letter, we study the nanocrystallization kinetics of Fe 85:5 Zr 4 Nb 4 B 5:5 Al 1 amorphous alloy by differential scanning calorimetry (DSC) and trans- mission electron microscopy (TEM). 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 1.5 mm, respectively. Isochronal and isothermal crystallization kinetics were studied by a Perkin- Elmer DSC-7 differential scanning calorimeter under nitrogen atmosphere. A sample mass of 3 mg was used in each DSC run. Samples of the amorphous ribbons were annealed in a conventional furnace under argon atmosphere. The annealed samples were left to cool slowly to room temperature. The microstructure was observed by a JEM-4010 trans- mission 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. Fig. 1 shows the isochronal DSC curve of the as- quenched sample in the temperature range 420± 585 8C taken at a heating rate of 10 8C min 1 . The ®gure reveals a single exothermic peak in this temperature range. No transitions were seen at temperatures below 420 8C. Fig. 2 shows a high resolution TEM (HRTEM) image and the selected area diffraction (SAD) pattern of the as-quenched sample. The halo ring in the SAD pattern con®rms that the as-quenched sample is amorphous, while the HRTEM image reveals fringe like regions (indicated by arrows) which, we think, are the medium range order (MRO) domains and represent the locations of quenched-in nuclei [3]. Although heterogeneous nucleation is most probable in the solidi®cation processes, the HRTEM image suggests the occur- rence of homogeneous nucleation. Fig. 3 shows a HRTEM image and the SAD pattern of the sample annealed for 1 h at 340 8C, which is below the start of the DSC peak. Again, the halo ring in the SAD pattern indicates that the sample is still amorphous at this stage. The HRTEM image reveals a dense distribution of MRO domains, suggesting further production of new nuclei upon annealing. Fig. 4 shows the bright ®eld image and 0261-8028 # 1998 Kluwer Academic Publishers -500 0 500 1000 1500 2000 2500 420 440 460 480 500 520 540 560 580 Temperature, (°C) Heat flow, (arbitrary units) Figure 1 The isochronal DSC curve of the as-quenched sample. Figure 2 HRTEM image and the SAD pattern of the as-quenched sample. MRO domains are indicated by arrows. 1125