Discontinuous coarsening behavior of Ni2MnAl intermetallic compound during isothermal aging treatment of Fe-Mn-Ni-Al alloys

The discontinuous reaction of the Ni2MnAl intermetallic phase was investigated during the aging of a solution-treated Fe-8.3Mn-8.2Ni-4.2Al alloy. During aging, Ni2MnAl lamellae formed at the prior austenite grain boundaries and twin boundaries and grew into the neighboring grains. The presence of continuously precipitated fine Ni2MnAl particles before the growth of the discontinuously precipitated lamellae was confirmed by dark-field transmission electron microscopy, and it was concluded that the present reaction is a type of discontinuous coarsening process, alpha' + Ni2MnAl (continuous precipitation) -> alpha + Ni2MnAl (discontinuous coarsening). The chemical driving force and the reduction of the total coherent strain energy were suggested to be the driving force for the discontinuous coarsening reaction.11Nsciescopu