Nanocluster-strengthened ferritic alloys were promising as structural materials because of their excellent high-temperature strength and radiation-damage resistance. Recently, Fu et al. (2007) predicted that vacancies play an essential role in the formation and stabilization of nanoclusters in these materials. Positron-lifetime spectroscopy was used to test this theoretical prediction in a nanocluster-strengthened Fe-based alloy. Nanoclusters (2 to 4nm in diameter) containing Ti, Y, and O were observed in a mechanically alloyed ferritic steel by atom-probe tomography. Vacancy clusters containing four to six vacancies have also been found in this material. In contrast, no vacancy clusters were detected in similar alloys containing no nanoclusters. These results indicate that vacancies were a vital component of the nanoclusters in these alloys.

Nanocluster-Associated Vacancies in Nanocluster-Strengthened Ferritic Steel as Seen via Positron-Lifetime Spectroscopy. J.Xu, C.T.Liu, M.K.Miller, H.Chen: Physical Review B, 2009, 79[2], 020204