Vacancy clustering and relaxation behavior in rapidly solidified B2 FeAl ribbons

The clustering and relaxation behavior of supersaturated thermal vacancies under annealing at 723 K and subsequent secondary defect formation were investigated in rapidly solidified Fe-40.4, 49.9 and 50.0 at.%Al ribbons by X-ray diffractometry, density measurement, differential scanning calorimetry, scanning electron microscopy, atomic force microscopy and transmission electron microscopy. Supersaturated thermal vacancies of (almost equal)0.3-2.5% were frozen into the as-spun ribbon. Most of the supersaturated vacancies were annihilated during a heat treatment, and the amount of annihilated vacancies was larger for a higher Al content. A large number of mesopores as well as dislocations were observed after the heat treatment, and the size of mesopores increased with increasing Al content. The results obtained suggest that mesopore formation is induced by clustering of supersaturated thermal vacancies. The activation enthalpy and kinetics of the vacancy clustering are discussed.