The recovery behaviour of vacancy-type defects created at 1000C in Fe 3 (Al 1- x Si x ) alloys was investigated by positron-lifetime measurements in samples cooled to room temperature by water quenching, air quenching and furnace cooling. In addition, a set of samples was aged for one week at 520C. After water quenching, measurements revealed a high concentration of thermal vacancies, and from the decrease of the average positron lifetime it was inferred that vacancy recovery was strongly composition-dependent. Greater decreases of the positron lifetime were found for Si-rich samples, suggesting diffusion enhancement as the Si concentration increased. For the Fe3Al alloy, the retained vacancy concentration depends strongly on the cooling rate. This was related to atomic ordering and a rebuilding of the D0 3 structure.

Defect Analysis of Fe3(Al1-xSix) Alloys by Positron-Lifetime Spectroscopy. Y.Ortega, N.de Diego, J.A.Jiménez, J.del Río: Philosophical Magazine Letters, 2004, 84[9], 547-54