Effect of precipitate phase on the plastic deformation behavior of Alloy 718: in-situ tensile experiment and crystal plasticity simulation

Abstract

In this study, in-situ tensile experiments were conducted on three samples containing different precipitate phases (δ, γ″ and γ′) to investigate the effects of these precipitates on the tensile deformation mechanisms of Alloy 718. Local plastic deformation was characterized by digital image correlation (DIC) and electron back-scatter diffraction (EBSD). The plasticity was analyzed in terms of slip, lattice rotation, slip transfer, and intergranular cooperative deformation. The dislocation accumulation is slower in the γ matrix, promoting uniform plastic deformation within grains via single slip, resulting in excellent intragranular deformation capability for the sample without any precipitates. In contrast, the γ″ and γ′ phases facilitate dislocation multiplication and impede dislocation motion, causing rapid dislocation pile-up within grains, leading to local stress concentrations. These stress concentrations can activate secondary slip systems early, resulting in uneven intragranular deformation and limiting the grains’ plastic deformation capacity for the sample with γ′′ and γ′. At grain boundaries, the δ phase hinders slip transfer, restricting the capacity for intergranular coordinated deformation, resulting in the formation of microcracks along the grain boundaries. These microcracks, along both the δ phase and the grain boundaries, contribute to the reduction in plasticity of the sample with δ phase. The effects of γ″ and γ′ phases are similar, as they limit grain deformation by influencing dislocation accumulation within grains, while the δ phase at grain boundaries reduces the tensile plasticity of Alloy 718 by impeding intergranular deformation coordination.