Local microstructure and its influence on precipitation behavior in hot deformed Nimonic 80a Original Research Article

The influence of local microstructure on the kinetics of heterogeneous carbide precipitation was investigated in hot deformed, commercial nickel-based superalloys Nimonic 80a. The as-deformed alloys were aged at 1073 K for different times, and precipitation characteristics were examined by transmission electron microscopy and small-angle neutron scattering. M23C6 precipitates were found to nucleate at grain boundaries, but in particular also on dislocation lines and boundaries of subgrains. In the early stages of ageing, the kinetics of carbide precipitation is enhanced and the average carbide size is smaller as a result of deformation. An influence of the degree of recrystallization on overall carbide kinetics is also found, which is attributed to differences in the amount of bulk carbides as compared to carbides at grain boundaries. In contrast to the behavior of carbides, the kinetics of the homogeneously distributed γ′ precipitates is not influenced by prior deformation.