Crystal growth mechanism of directionally solidified Fe-Al-Ta eutectic composites at higher solidification rates

Fe-Al-Ta eutectic composites with solidification rates of 650 mu m/s, 700 mu m/s, 800 mu m/s and 900 mu m/s were prepared by a modified Bridgman directional solidification technique in order to study the microstructure and crystal growth mechanism. The composition, microstructure, preferential orientations of Fe-Al-Ta eutectic composites were investigated by EDX, SEM, SAED, respectively. The results show that the microstructure of Fe-Al-Ta eutectic composites presents short rods and spheres, and microstructure is gradually refined with the increase of solidification rates. It is composed of Fe (Al, Ta) matrix phase and Fe2Ta (Al) reinforcement phase. The lamellar/rod spacing is decreased with the increase of solidification rates. It was also be predicted by Kurz Fisher model, Hunt-Lu model and Trivedi model, and the experimental results is relatively close to the Hunt-Lu model. The morphologies of solid/liquid interface at higher solidification rates were forecasted by M S and K-F model, and the theory calculation is consistent with experimental results well. The preferential orientations of Fe-Al-Ta eutectic composites at higher solidification rates were studied by selected area electron diffraction (SAED).