AN ANALYSIS OF THE MICROSTRUCTURE OF RAPIDLY SOLIDIFIED AL-8 WT PCT FE POWDER

Rapidly solidified powders exhibit four microstructures with increasing particle diameter in the size range 5 mu m to 45 mu m: microcellular alpha -Al; cellular alpha -Al; alpha -Al plus Al//6Fe eutectic; and Al//3Fe primary intermetallic structure. Small powder particles undercool prior to solidification and typically exhibit a two-zone microcellular-cellular structure where there is a transition from solidification dominated by internal heat flow during recalescence with high growth rates (microcellular) to solidification dominated by external heat flow and slower growth rates (cellular). The origin of the two-zone microstructure is interpreted as growth controlled primarily by solute redistribution.