Optimisation of processing of intermetallics for engineering applications

EPSRC research grant GR/J/32572

Summary of the final report

Four processing methods have been employed for the production of alloys based on or around the composition Fe - 25a% Al. The major effort was concentrated on optimisation of the conventional ingot/extrusion/hot rolling route and on twin roll strip casting. Methods involving co-rolling of elemental foils with solid state homogenisation and consolidation, and spray forming were also explored.
The ingot/extrusion/hot rolling processing route was found to be a viable option for iron aluminides containing 23-28a% Al. Processing parameters for hot working of Fe-25a% Al were developed through rolling load measurements and plane strain compression tests. The processing temperature 'window' for hot rolling of Fe-25 a% Al is quite narrow (700 - 800C) due to excessive grain growth at higher temperatures and a rapidly increasing flow stress at lower temperatures associated with the formation of ordered structures. Control of the hot rolling process produced a finer grained, partially recrystallised, work hardened microstructure, with improved tensile properties (UTS, PS and elongation), compared with hot rolling at 1000C.
Twin-roll strip casting is a viable method for direct production of iron aluminide strip or plate. However the tensile properties of such strip cast material was variable. This variability stemmed from the presence of cast-in defects, such as laps. The best properties in aluminides derived from the strip cast material however were comparable with the ingot processed material.
Co-rolling of elemental foils was shown to be a contender for solid state formation of intermetallics, but the material requires further processing.
The use of spray deposition for intermetallics has potential as yet to be fully explored, though it is more likely to be useful as a coating technique than for producing bulk intermetallics.

Contact:

Dr. R.A. Buckley,
Department of Engineering Materials,
University of Sheffield,
Mappin Street, Sheffield S1 3JD
Telephone: 0114 222 5508
Fax: 0114 222 5943