MICROSTRUCTURE OF A RAPIDLY SOLIDIFIED Al-4V-2Fe ULTRAHIGH STRENGTH ALUMINUM ALLOY

Microstructure of a rapidly solidified Al-4V-2Fe alloy has been examined in detail by means of transmission electron microscopy and atom probe field ion microscopy. It is composed of a mixture of α-Al and amorphous phases. α-Al grains are relatively large (400 nm), but nanoscale domains of amorphous phase are trapped in the fcc grains. The interface between the α-Al and amorphous phases are very irregular and solute elements are partitioned into the amorphous phase. The evolution of such microstructure is explained based on an unstable interface due to constitutional supercooling during the solidification process. Enrichment of Fe atoms is observed at some interfaces. Rejected solutes during crystallization of α-Al are believed to be enriched at the advancing α/liquid interface and this liquid is solidified as amorphous phase, resulting in nanoscale amorphous regions embedded in fcc grains.