Nanoporous surfaces are formed in B2-type FeAl single crystals by quenching into iced water, followed by surface treatment and aging heat treatment. From our previous works, it was indicated that the nanoporous phenomenon is caused by the clustering of supersaturated thermal vacancies. In this study, the clustering process of supersaturated thermal vacancies was systematically investigated by transmission electron microscopy (TEM). An irreversible exothermic peak was detected for as-quenched specimens by differential scanning calorimetry (DSC). The isochronal changes of surface morphology and substructure around the exothermic peak temperature were clarified by TEM observation. The average size of the surface pores monotonously increased with increasing the temperature. Dislocations whose Burgerse vectors are parallel to <100> existed in the isochronally-heated single crystals, and its density was changed with heat treatment temperature. On the other hand, there was no dislocation zone from surface to the depth of several tens nanometers. A growth model of the surface pores is discussed
