Effect of temperature on the tensile properties and dislocation structures of FeAl alloys

Tensile deformation and fracture behavior of three B2 structural intermetallic FeAl alloys - one binary alloy (Fe-36.5Al) and two ternary alloys (Fe-36.5Al-5Cr and Fe-36.5Al-2Ti) - were investigated at different temperatures between room temperature and 1000 degrees C. The specimens were prepared by hot-rolling of ingots and heat treatment. The elongation to failure of the alloys was found to increase when the testing temperature increased from room temperature to 300 degrees C, decrease 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 alloys decreased slowly until 500 degrees C, then increased slightly, and 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 temperatures (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 binary Fe-36.5Al alloy. The fracture modes of these alloys when deformed at room temperature are a mixture of intergranular fracture and transgranular cleavage. With increase in temperature, the percentage of transgranular fracture generally increased, except for that observed around 500 degrees C. Dislocations with a [111] Burgers vector are found in the FeAl alloy deformed at higher temperatures. It is suggested that the good ductility of the FeAl alloys deformed at higher temperatures may 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.