Processing and alloying effects on tensile and impact properties of FeAl alloys

Two series of iron aluminide alloys [Fe-36-38Al (at.%)] were produced by in got metallurgy or powder metallurgy methods, to examine the effects of proc essing and of slight changes in chemical composition on the microstructure and mechanical properties. For the first series of alloys, the powder metal lurgy materials developed a very fine grain size when extruded at 950 or 10 00 degrees C, much finer than the initial powder particle size. Extrusion a t 1100 degrees C resulted in a coarser grain size. The fine-grained powder alloys showed excellent strength and ductility, and high levels of energy a bsorption in impact tests. The high levels of energy absorption were caused by extensive crack deflection along the remnant oxide layers from the prio r particle boundaries; these boundaries had been elongated and oriented per pendicular to the notch by the extrusion process. The coarse-grained materi al, which had larger, mon isolated oxide particles, had slightly lower duct ility, but had much poorer impact properties, with no crack deflection. Ing ot metallurgy alloys of similar composition, extruded at 900 degrees C, had lower strength and ductility than the powder materials. The addition of bo ron (0.021 at.%) resulted in a change of fracture mode in the impact tests from intergranular to transgranular, which significantly increased the ener gy absorption. A second series of cast FeAl alloys examined the effect of c hanges in the levels of Zr, C, and B, as compared to the first series of al loys. Increases in the Zr and C resulted in increases in the strength and s light decreases in the ductility. Numerous flaws, apparently created during machining of the cast material, were observed on the surfaces of the impac t specimens, which still showed some energy absorption when tested. Differe nt fracture modes, including cleavage, intergranular, and ductile tearing, were observed on the fracture surfaces of various impact specimens. (C) 199 8 Published by Elsevier Science S.A. All rights reserved.