EFFECT OF TEMPERATURE ON THE TENSILE PROPERTIES AND DISLOCATION-STRUCTURES OF FEAL ALLOYS

Tensile deformation and fracture behavior of three B2 structural inter metallic FeAl alloys - one binary alloy (Fe-36.5Al) and two ternary al loys (Fe-36.5Al-5Cr and Fe-36.5Al-2Ti) - were investigated at differen t temperatures between room temperature and 1000 degrees C. The specim ens were prepared by hot-rolling of ingots and heat treatment. The elo ngation to failure of the alloys was found to increase when the testin g temperature increased from room temperature to 300 degrees C, decrea se slightly from 300 to 500 degrees C, and increase dramatically from 600 to 1000 degrees C. On the other hand, the yield strength of the al loys decreased slowly until 500 degrees C, then increased slightly, an d decreased dramatically between 700 and 1000 degrees C. The abnormal yield effect of these alloys occurred in the temperature range 500-700 degrees C. The addition of chromium or titanium was found to improve the tensile properties of FeAl alloys, especially at elevated temperat ures (800-1000 degrees C). The ternary Fe-36.5Al-5Cr or Fe-36.5Al-2Ti alloy had a higher elongation and higher yield strength than the binar y Fe-36.5Al alloy. The fracture modes of these alloys when deformed at room temperature are a mixture of intergranular fracture and transgra nular cleavage. With increase in temperature, the percentage of transg ranular fracture generally increased, except for that observed around 500 degrees C. Dislocations with a [111] Burgers vector are found in t he FeAl alloy deformed at higher temperatures. It is suggested that th e good ductility of the FeAl alloys deformed at higher temperatures ma y result from glide as well as climb of the dislocations with a [111] Burgers vector during deformation. (C) 1998 Elsevier Science S.A. All rights reserved.