Processing iron aluminides by heavy deformation for improved room temperature strength-ductility and for high temperatur
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Processing iron aluminides by heavy deformation for improved room temperature strength-ductility and for high temperature creep strength David G. Morris and Maria Antonia Muñoz-Morris Department of Physical Metallurgy, CENIM, CSIC, Avenida Gregorio del Amo 8, 28040 Madrid, Spain ABSTRACT Iron aluminides show many interesting properties, but still show relatively poor ductility at room temperature and only moderate creep resistance at temperatures above about 600ºC. Processes of severe plastic deformation have been investigated for a wide range of ductile alloys over the past decade, but have hardly been considered for intermetallics. This presentation discusses two studies aimed at refining microstructure by the use of severe plastic deformation of iron aluminides. The first considers processing Fe3Al by heavy cold rolling, followed by annealing for recovery or recrystallization, with an objective of refining grain size to improve strength at the same time as ductility. The high strength and poor ductility of the work hardened material leads to a danger of cracking during rolling, which is a problem for manufacturing large quantities of healthy material. Suitable rolling and recovery treatments can, nevertheless, lead to strong materials with some plastic ductility. A different technique of multidirectional, high-strain and high-temperature forging applied to a boride-containing Fe3Al alloy produces a material with large grain size and refined dispersion of boride particles. These particles lead to a considerable increase in creep strength under conditions of moderate stresses at temperatures around 700ºC. This high-strain forging technique can be seen as an intermediate processing method between conventional wrought metallurgy and mechanical-alloying powder metallurgy. This technique offers the possibility to improve high temperature behaviour of such intermetallics containing second-phase dispersions, and can be scaled to produce large quantities of high-quality material. INTRODUCTION The present overview examines two separate studies which attempted to improve the mechanical properties of iron aluminides by processing using very high plastic strains. Such processing, generally carried out using special techniques, is categorized under the title of severe plastic deformation, and leads to a refinement of the microstructure, including both the grain size and any second phase particles that may be present [1]. Iron aluminides have reasonably interesting mechanical properties, and also show excellent resistance to corrosion in many industrial environments [2], but there remains a need to improve both ductility/toughness at room temperature as well as creep resistance at temperatures above 600ºC. The microstructures necessary for obtaining these two properties are different, and typically therefore require different alloy compositions and different processing conditions. Two such alloys and processing methods are considered here, whereby either the ductility or the creep resistance may be improved. These studies consi
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