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

An electron backscattered diffraction technique has been used to investigate crystallographic features of a superplastic coarse-grained Fe-27 at% Al alloy. Alloy samples studied have been tensile tested in a temperature range between 600 and 800°C in air under an initial strain rate of 1×10⁻⁴ s⁻¹. As a result of dynamic recovery and recrystallization, the grain 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°C). Upon further deformation at 700°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°C), dynamic recovery and recrystallization occur significantly, resulting in grain refinement and hence superplasticity. Refined grains thus formed maintain crystallographic relationships with parent grains.