Electron backscattered diffraction study on superplastic properties of coarse-grained Fe-27 at% Al

An electron backscattered diffraction technique has been used to investigat e crystallographic features of a superplastic coarse-grained Fe-27 at% Al a lloy. Alloy samples studied have been tensile tested in a temperature range between 600 and 800 degrees C in air under an initial strain rate of 1 x 1 0(-4) s(-1). As a result of dynamic recovery and recrystallization, the gra in structure undergoes four major transitions: subgrain-boundary formation, grain-boundary migration, formation and growth of recrystallized grains. A model based on the microstructural evolution is described. Subgrains form during an initial stage of high-temperature deformation when deformation is conducted at low temperature (600 degrees C). Upon further deformation at 700 degrees C, grain boundaries migrate, resulting in the formation of new grains. When deformation is made further to a larger elongation or at even higher temperature (800 degrees C), dynamic recovery and recrystallization occur significantly, resulting in grain refinement and hence superplasticit y. Refined grains thus formed maintain crystallographic relationships with parent grains. (C) 1999 Elsevier Science Ltd. All rights reserved.