MICROSTRUCTURE OF A RAPIDLY SOLIDIFIED AL-4V-2FE ULTRAHIGH STRENGTH ALUMINUM-ALLOY

The microstructure of a rapidly solidified Al-4V-2Fe alloy has been ex amined in detail by means of transmission electron microscopy and atom probe field ion microscopy. It is composed of a mixture of alpha-Al a nd amorphous phases. alpha-Al grains are relatively large (400 nm), bu t nanoscale domains of amorphous phase are trapped in the fcc grains. The interfaces between the alpha-Al and amorphous phases are very irre gular and solute elements are partitioned into the amorphous phase. Th e evolution of such a microstructure is explained on the basis of an u nstable interface due to constitutional supercooling during the solidi fication process. Enrichment of Fe is observed at some interfaces. Sol utes rejected during crystallization of alpha-Al are believed to be en riched at the advancing alpha/liquid interface and this solute-enriche d liquid solidifies as amorphous phase, resulting in nanoscale amorpho us regions embedded in fee grains. (C) 1998 Elsevier Science S.A. All rights reserved.