Mechanism of disordering in FeAl under electron irradiation

Abstract

The disordering process in FeAl with the B2-type superlattice has bean examined during irradiation in a high voltage electron microscope. The long-range order parameter decreases exponentially with time under irradiation at temperatures from -150 to 295°C. The disordering cross-section (K) for irradiation along the ⟨100⟩ direction is almost the same as that along the ⟨110⟩ direction in the electron-energy range 0.25–1.25 MeV.

Experimental results are analysed using theories based on two disordering mechanisms; (1) ⟨111⟩ replacement collisions, and (2) atomic displacement and subsequent random recombination of displaced atoms with vacancies. The unsuccessful application of the former mechanism and the successful application of the latter mechanism to the results suggest that recombination of displaced atoms with vacancies on the opposite sublattice is the dominant process for disordering in electron irradiated FeAl. The dependence of K on the irradiation temperature is also discussed in terms of the migration of interstitial atoms.