Defect analysis of Fe₃(Al_1–xSi_x) alloys by positron-lifetime spectroscopy

The recovery behaviour of vacancy-type defects created at 1000°C in Fe3(Al1– x Si x ) alloys has been 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 520°C. After water quenching, measurements reveal a high concentration of thermal vacancies, and from the decrease of the average positron lifetime it is inferred that vacancy recovery is strongly composition-dependent. Greater decreases of the positron lifetime were found for Si-rich samples, suggesting diffusion enhancement as the Si concentration increases. For the Fe3Al alloy, the retained vacancy concentration depends strongly on the cooling rate. This is related to atomic ordering and a rebuilding of the D03 structure.