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

The development of intermetallic γ′, γ″ precipitates and γ′/γ″ co-precipitates in Inconel 706 during exposure at a service temperature of 750 °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 γ′/γ and γ″/γ interfaces. The total strain energy per γ″ and γ′ precipitates in matrix is three times larger as the total strain energy per γ′/γ″ co-precipitate. We find that a γ″-precipitate is energetically unstable and tends to merge with a γ′-precipitate creating a γ′/γ″ co-precipitate. The long-range stress field can considerably reduce the mean normal stresses around γ″/γ interfaces.