Numerous thermal vacancies were frozen into FeAl B2-ordered alloy ribbons by a conventional rapid-solidification technique. During heat treatment at 723K, clustering of the supersaturated vacancies generated a large number of nano-pores, particularly near to surfaces, thus creating nano-porous surfaces. The nano-porous surface structure was confirmed by scanning electron microscopy and atomic force microscopy. The behavior of this vacancy clustering was examined by using differential scanning calorimetry. An exothermic irreversible peak, probably due to vacancy clustering, was observed at around 800K; giving an activation energy of about 1.17eV. Nano-pore formation was also observed during in situ heating experiments in a transmission electron microscope. The pores had a specific morphology and crystallography, with pore surfaces faceting towards {100} planes. The results suggested that vacancy clustering was a unique process which permitted the efficient preparation of nano-porous surfaces.

Nanoporous Surfaces of FeAl Formed by Vacancy Clustering. K.Yoshimi, S.Hanada, T.Haraguchi, H.Kato, T.Itoi, A.Inoue: Materials Transactions, 2002, 43[11], 2897-902