Abstract
Aging behavior of Al-Fe alloys was examined by transmission electron microscopy and Mössbauer spectroscopy to understand the good mechanical strength maintained at elevated temperatures. Following results were obtained:
(1) A fine iron rich eutectic phase at cell walls was found stable up to 400°C, above which needle shaped FeAl3 nucleated at walls.
(2) Iron concentration in the matrix remained high up to 400°C. However, it decreased upon growth of FeAl3 needles.
(3) An intermediate phase appeared in the matrix even below 250°C. It transformed at higher temperatures and finally decomposed above at 350°C.
(4) Boundary precipitation of metastable FeAl3 occurred at 400°C, while the Oswald growth of FeAl3 in the matrix was prominent above at 450°C.
These results suggest the unusually slow diffusion of iron atoms in the alloy and can explain that the dispersion strengthening effect is maintained up to 350°C
