A study of precipitation in DO3 ordered Fe-Al-Nb alloy

Precipitation and ordering has been examined in Fe3Al-base alloy with a small addition of Nb. At low temperatures the alloy shows DO3 order with no precipitation, at least for short annealing times. At intermediate temperatures, 700-750 °C, planar precipitates of a phase with L21 structure form, which transform at longer times and high temperatures to blocky precipitates of the stable Laves phase of C14 structure. The L21 precipitates form on {001} planes, coherently with the ordered matrix, while the C14 particles form in a {1¯010}C14//{1¯01}matrix relationship with <12¯10>C14 approximately parallel to the 〈010〉matrix and 〈0001〉C14 approximately parallel to the 〈101〉matrix. These particles grow relatively quickly in the intermetallic matrix, and hence are unsuitable for matrix strengthening at temperatures above about 750 °C.