Coarsening kinetics of lamellar microstructures: Experiments and simulations on a fully-lamellar Fe-Al in situ composite

A very fine lamellar microstructure consisting of the intermetallic phases FeAl and FeAl2 forms in binary Fe-Al alloys due to the eutectoid reaction Fe5Al8 ↔ FeAl + FeAl2, which takes place in the Al range between 56.0 and 64.4 at.% at 1095 °C. A fully lamellar microstructure is obtained at the eutectoid composition 60.9 at.% Al. The initial lamellar spacing λ0 of as-cast material is 200 ± 40 nm. In this study, the kinetics of coarsening of the FeAl + FeAl2 lamellar microstructure is investigated at four different temperatures in the range 600 °C-1000 °C with holding times from 10 min to 7000 h. It is found that the increase of the lamellar spacing can be described as λ3=λ03+kt. The value obtained for the activation energy proves that the lamellar coarsening is a volume-diffusion-controlled process. Besides the experimental investigations, phase-field modeling is used to simulate the lamellar coarsening. The results are in good agreement with the experimental observations with regard to the evolution of the lamellar morphology and the value of the coarsening exponent.

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