Modeling the evolution of intergranular helium bubbles in nickel using the included phase model

Neutron irradiation of Nickel alloys produces vacancies due to damage, and helium from decay of activation products within the solid matrix which accumulate in inter-and-intra granular bubbles. Bubble formation contributes to dimensional changes and potential degradation of bulk material properties. The presence of a large number of intergranular bubbles may contribute to a reduction in the intergranular fracture toughness from a reduction of grain boundary contact. In this work we investigate the time-evolution of intergranular helium bubbles using the Included Phase Model (IPM), a novel mesoscale technique which describes the morphology of interfaces as a parametric surface. The IPM preserves key features of phase-field type models with a significantly reduced computational cost. The model accounts for vacancies and helium in the solid matrix and void phase. Transport of the species and evolution of the phases is driven by the minimization of the interfacial energy, the energy of vacancies on the grain boundary, and the elastic energy of the surrounding matrix. The characteristics of the simulated bubble populations are discussed in relation to TEM results from irradiated Inconel X-750.