Grain boundary barrier strength and local stress evolution: Geometric compatibility effects and the curious case of twin boundaries

In situ high-resolution electron backscattered diffraction (HR-EBSD) deformation was combined with concurrent atomistic-continuum (CAC) simulations to study the interactions between dislocations and grain boundaries in Ni. The stress fields near dislocation pileups measured and modeled at multiple strain levels were used to assess the barrier strength of grain boundaries to dislocation slip. With the exception of twin boundaries, a positive correlation was found between the barrier strength of a boundary and the geometric misalignment of the slip systems in the two adjacent grains. Dislocation interactions with coherent twin boundaries resulted in little to no stress localization, while incoherent twin boundaries presented considerable barriers to slip transfer, resulting in significant stress localization. The evolution of local stress in the boundary vicinity as a function of applied strain was found to follow a stress buildup and release pattern, with the magnitude of stress buildup and release dependent on the geometric misalignment. At high applied strain levels, diffuse stress fields formed near grain boundaries, which were attributed to junctions and tangles formed as a result of stress homogenization mechanisms.