Structural modifications during heating of bulk nanocrystalline FeAl produced by high-pressure torsion

The deformation-induced nanostructure developed during high-pressure torsion of B2 long-range ordered FeAl is shown to be unstable upon heating. The structural changes were analyzed using transmission electron microscopy, differential scanning calorimetry and microhardness measurements. Heating up to 220 °C leads to the recurrence of the chemical long-range order that is destroyed during deformation. It is shown that the transition to the long-range-ordered phase evolves in the form of small ordered domains homogeneously distributed inside the nanosized grains. At temperatures between 220 and 370 °C recovery of dislocations and antiphase boundary faults cause a reduction in the grain size from 77 to 35 nm. Grain growth occurs at temperatures above 370 °C. The evolution of the strength monitored by microhardness is discussed in the framework of grain-size hardening and hardening by defect recovery.