Precipitate and dislocation-density interactions affecting strength and ductility in inconel alloys

Grain and precipitate morphologies, orientations, and distributions in precipitation hardened nickel alloy 718 are directly affected by material processing, thermal and mechanical history, and tailored to optimize its thermo-mechanical behavior in service. A computational approach based on a dislocation-density crystalline plasticity formulation, was used to investigate and identify dominant microstructural mechanisms and defects, such as perfect and partial dislocation-densities, in an experimentally characterized specification of 718 alloy. The role of perfect and partial dislocation densities and their interaction with the material microstructure, affecting the mechanical behavior of the alloy were investigated. Different precipitate volume fractions were used to characterize and identify these interactions and behavior. Using an integrated experimental and modeling approach, the δ phase precipitated along grain boundaries in the form of elongated rods is shown to be a source of dislocation-density accumulations. Interactions include strengthening, achieved by impeding the motion of dislocations by the coherent precipitates, and shear deformation competition, associated with shear slip or plasticity accumulation between the preferentially oriented slip systems of the precipitates and the matrix.