Creep behavior of intermetallic Fe-Al and Fe-Al-Cr alloys

A study of creep behavior of several alloys based in the Fe-Al and Fe-Al-Cr systems ranging in aluminium from 21.7 to 48 at.% was undertaken. The alloys were produced by induction melting and possess a coarse and equiaxial microstructure, with a grain size of about 500 mu m. Compression tests at rates from 10(-5) to 10(-2) were conducted at temperatures ranging from 700 to 1000 degrees C under a protective atmosphere of argon to minimize oxidation. Analysis of the stress-strain data revealed in the binary alloys a stress component of about 3 that suggest that creep is controlled by viscous glide of dislocations. For an aluminium content above 30 at.%, the activation energy for creep does not vary very much with the aluminium concentration and values ranging from 360 to 395 kJ mol(-1) were obtained. On the other hand, the ternary alloys present an improvement in strength in the high temperature compressive creep. A stress exponent of 4-5 is observed in this case that suggest that creep is controlled by dislocation climb. An activation energy for creep of about 505 kJ mol(-1) was deduced for the alloy containing 30 at.% Al and 10 at.% Cr.