Fig. 1. Estimated cooling rates of the droplets as a function of droplet size d.

Fig. 2. XRD patterns and phase identifications of the droplets as a function of size range.

Fig. 3. SEM micrograph of the drop tube cooled sample showing blocky Al13Fe4, Al13Fe4 needles and α-Al matrix.

Fig. 4. Microstructures of rapidly solidified Al-2.85 wt% Fe: (a) 850-500 µm and (b) 500-300 µm droplets (circles showing the nucleation start zone).

Fig. 5. Typical microstructures of large droplets 850 µm < d < 500 showing (a) magnified image of the nucleation region, microcellular region, (b) dendritic region, (c) magnified image of the dendritic region and (d) eutectic region.

Fig. 6. Microstructures of (a) 300 μm < d < 212 μm, (b) 212 μm < d < 150 μm, (c) 150 μm < d < 106 μm, (d) 106 μm < d < 75 μm and (e) 75 μm < d < 53 μm size fractions, with arrows showing boundaries of growing dendrites and circles showing the nucleation start zones. (f) Enlarged view of the 106 μm < d < 75 μm sieve fraction showing that the interdendritic eutectic remains of the lamella morphology irrespective of sieve fraction/cooling rate.

Fig. 7. SEM BSE micrographs taken from the solidification start zone of (a) 106-75 µm powder showing cellular α-Al surrounded by lamella-like eutectic, (b) 106-75 µm powder showing divorced eutectic with intermetallics with various size and morphology, (c) 75-53 µm powder depicting divorced eutectic on which dendritic α-Al grows with lamellar-like intermetallic and (d) magnified image of solidification zone of (c).

Fig. 8. Secondary dendrite arm spacing (SDAS) as a function of average powder size.

Fig. 9. Dissolved Fe in α-Al as a function of average cooling rate.

Fig. 10. Composition of the interdendritic eutectic as a function of average cooling rate.

Fig. 11. Eutectic volume per cent as a function of the average cooling rate.

Fig. 12. Interdendritic eutectic spacing as a function of average cooling rate.

Fig. 13. (a) TEM bright field image of the rod-like eutectic, (b) TEM diffraction pattern of point 1 showing the diffraction pattern of Al6Fe along the [1$\bar{1}$0] zone axis, (c) TEM bright field image of the lamella-like interdenritic eutectic, (d) TEM diffraction pattern of point 2 depicting the diffraction pattern of Al13Fe4 along the [$\bar{17}$4] zone axis, (e) TEM bright field image of point the intermetallic formed between rod-like eutectic and interdendritic eutectic, (f) TEM diffraction pattern of point 3 depicting Al13Fe4 along the [1$\bar{2}$3] zone axis.

Fig. 14. Microhardness value (in HV0.01) as a function of cooling rate.

Fig. 15. Eutectic growth velocity (right-hand axis) and interfacial undercooling (left-hand axis) for the Al-Al13Fe4 lamellar eutectic, estimate from the lamellar spacing.

Fig. 16. Estimated location of the Al-rich side of the eutectic coupled zone for the growth of Al-Al13Fe4 eutectic.