High temperature load relaxation behavior of superplastic iron aluminides

Abstract

Superplastic deformation and high temperature load relaxation behavior of coarse-grained iron aluminides have been investigated in this study. Iron aluminides with compositions of Fe-28 at.% Al and Fe-28 at.% A1-5 at.% Cr were prepared and thermomechanically treated to obtain an average grain size of about 500 mum A series of load relaxation tests was conducted at temperatures ranging from 600 to 850 degreesC. The flow curves obtained from load relaxation tests were found to have a sigmoidal shape and to exhibit stress vs. strain rate data in a very wide strain rate range from 10(-7)/s to 10(-2)/s. Tensile tests have been conducted at 850 degreesC and at various initial strain rates ranging from 3x10(-5)/s to 1x10(-2)/s to investigate the superplastic deformation behavior. Maximum elongation of similar to 500 % was obtained at the initial strain rate of 3x10(-5)/s and the maximum strain rate sensitivity was round to be 0.68. Microstructural observation through the optical microscopy has been carried out on the deformed specimens and it has revealed the evidences for grain boundary migration and grain refinement to occur during deformation, suggesting the dynamic recrystallization mechanism as reported earlier. The activation energy was evaluated as 387 kJ/mol in the strain rate range from 10(-4)/s to 10(-2)/s, which is very close to that for creep deformation in Fe3Al alloys.