The Development of FE-AL Intermetallics

Abstract

The intermetallics based on aluminides have long been known for their excellent resistance to high-temperature oxidation. However, for use in structural components the poor ductility at ambient temperatures has always been felt as a stumbling block. Interest in these materials has been revived recently, after achieving some success in improving the ductility at ambient temperatures and creep at elevated temperatures in titanium aluminides. For the iron aluminides, too, similar methodologies have been attempted, namely alloying with elements such as titanium, boron, molybdenum, chromium, silicon and manganese, as well as grain refinement for improving high-temperature creep and room-temperature ductility. Raising the creep resistance close to 600-degrees-C and improving the ambient-temperature ductility to around 6% have been the major immediate aims. Attempts are also being made to improve the high-temperature fatigue and creep properties in these materials, particularly by pushing the stability temperature of ordered D0(3) upwards. It is now visualized that once the above properties are achieved, the iron aluminides, particularly the types based on Fe3Al, could offer themselves as excellent candidate materials for structural purposes. Their attractiveness also stems to a large extent from their low cost, as they contain only abundantly occurring materials. The present work examines two routes for introducing ductility in the Fe3Al-based materials: one by ternary-quarternary additions and the other by grain refinement. Structural studies have been made on materials obtained through conventional casting as well as through rapid solidification with minor alloy additions. The results confirm that Fe3Al-based alloys, even when air-melted, are amendable to a high degree of hot working and could be made to display improved ductility at room temperature by a careful control of the chemistry. Rapidly solidified ribbons also show reasonably good bonding during high-temperature compaction. Ordering in these alloys is not suppressed even by rapid solidification