Electron Microscopy of Rapidly Solidified Weldments in a Powder Metallurgy Al-Fe-Ce Alloy.

摘要

Al-Fe-Ce alloys are rapid-solidification/powder metallurgy (RS/PM) products that offer significant advantages over conventional ingot metallurgy (IM) aluminum alloys for elevated-temperature applications. Through rapid solidification, the formation of coarse, primary intermetallics is suppressed and solidification instead occurs to a primary chi-aluminum structure. Subsequent powder consolidation and thermomechanical processing promote the formation of a high volume fraction (25 to 35%) of extremely fine thermally stable dispersoids in a matrix of submicrometer chi-grains. This unique microstructure provides moderate to high room-temperature mechanical properties up to 300 C. Recent work has demonstrated that capacitor-discharge welding can successfully generate high-integrity joints in Al-Fe-Ce alloys. The extremely rapid heating and cooling rates associated with this process allow the generation of a rapidly solidified fusion zone without degradation to the surrounding base-metal microstructure. In addition, the simultaneous application of pressure during fusion-zone solidification suppresses the formation of hydrogen-induced porosity. In the original study the investigation of weld-zone solidification characteristics was limited by the exclusive use of light microscopy for microstructure characterization. The purpose of the present work was to characterize capacitor-discharge weld-solidification phenomena in greater detail through the use of transmission electron microscopy (TEM). Reprints. (kt)