Microstructural characterization and solidification behavior of atomized Al-Fe powders

The effect of solidification history on the resultant microstructure in ato mized Al - 2.56 wt% Fe and Al - 6.0 wt% Fe powders was studied, with partic ular emphasis on droplet size, undercooling, and phase stability. The atomi zed Al - Fe powders exhibited four microstructural features, i.e., Al3Fe ph ase (now known as Al13Fe4), Al + Al6Fe, alpha - Al dendrite, and a predendr itic microstructure. The presence of these phases was noted to depend on al loy composition and a kinetic phase competitive growth mechanism due to the initial undercooling experienced by the powders. The occurrence of structu res of the predendritic, cellular, and/or dendritic type was properly predi cted by the theory of dendrite growth into undercooled alloy melts for the case of large undercoolings.