Recovery, recrystallization and grain growth in Fe3Al-based alloys

The recovery, recrystallization and grain growth of particle-free and particle-containing Fe3Al intermetallics with a total warm reduction of 70% were investigated in the temperature range from 750 to 1115 °C. The physical phenomena during annealing were characterized and analyzed based on the observations of microstructure, measurement of long-range order degree and determination of micro-hardness. The reordering occurs due to the removal of antiphase boundary trails resulting from the dislocation rearrangement during annealing. The micro-hardness depends on both the dislocation density and the change of long-range order degree. The addition of alloying elements affects the dependence of hardness on reordering. It also has a great effect on the recovery and recrystallization. The recrystallized nuclei are formed by preferential subgrain growth and grain boundary migration. Due to strong anisotropy of Fe3Al-based alloys, the grain boundary migration resulting from inhomogeneous deformation was frequently observed and the distribution of grain size after annealing was also inhomogeneous. The recrystallization kinetics follows the Kolmogorov-Johnson-Mehl-Avrami (KJMA) relationship. Long-range order and second phase are beneficial in decreasing the grain-boundary mobility. The grain growth kinetics of Fe3Al intermetallics investigated follows the conventional power law equation with a high grain growth exponent of more than 4. Abnormal grain growth in the Fe–28% Al–5% Cr–0.1% Zr–0.5% Mo–0.5% Nb–0.05B% (at.%) alloy was found when it was annealed at 1115 °C for 72 h.