Coarsening of a multimodal nickel-base superalloy

The coarsening of gamma'-Ni3Al precipitates in the nickel superalloy Ni115 has been examined and compared to the results of a numerical model based on LSW coarsening theory. Ni115 has a gamma' fraction of around 60%, and at the coarsening temperatures of interest the gamma' distribution is bimodal, with two populations similar to 5 nm and similar to 90 nm in radius. It is found that during the initial transient (around 2000 h at 800 degrees C), the fine gamma' dissolve, leading to a rapid increase in the mean radius followed by a plateau. At long times, the expected steady-state unimodal t(1/3) coarsening is observed. The model reproduces these features in form and approximately in magnitude, a first for LSW model-experiment comparisons in nickel superalloys. (C) 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.