(gamma)/(gamma)" Co-precipitation in Inconel 706 alloy: A 3D finite element study

The development of intermetallic (gamma)ʹ,(gamma)" precipitates and (gamma)ʹ/(gamma)" 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 (gamma)ʹ/(gamma) and (gamma)"/(gamma) interfaces. The total strain energy per (gamma)"and (gamma)ʹ precipitates in matrix is three times larger as the total strain energy per (gamma)ʹ/(gamma)" co-precipitate. We find that a (gamma)"-precipitate is energetically unstable and tends to merge with a (gamma)ʹ-precipitate creating a (gamma)ʹ/(gamma)" coprecipitate. The long-range stress field can considerably reduce the mean normal stresses around (gamma)"/(gamma) interfaces.