γ′/γ" Co-precipitation in Inconel 706 alloy:: A 3D finite element study

The development of intermetallic gamma', gamma" precipitates and gamma'/gamma" co-precipitates in Inconel 706 during exposure at a service temperature of 750 degrees C is investigated. The distributions of elastic strain energy and mean normal stresses around the interfaces of precipitates arise from the lattice-mismatch and are calculated by means of three-dimensional finite element (FE) analysis. The highest energy density is found at the gamma'/gamma and gamma"/gamma interfaces. The total strain energy per gamma" and gamma' precipitates in matrix is three times larger as the total strain energy per gamma'/gamma" co-precipitate. We find that a gamma"-precipitate is energetically unstable and tends to merge with a gamma'-precipitate creating a gamma'/gamma" co-precipitate. The long-range stress field can considerably reduce the mean normal stresses around gamma"/gamma interfaces. (c) 2005 Elsevier B.V. All rights reserved.