Understanding microstructure-sensitive deformation mechanisms in AMed IN738LC superalloy via in-situ EBSD-DIC

Additive manufacturing (AM) produces polycrystalline alloys with heterogeneous microstructures, high initial dislocation densities, and residual stresses. To probe their influence on microstructure-sensitive deformation behavior, we develop a “trace-back” framework integrating DIC and EBSD to map strain, geometrical necessary dislocations (GNDs), and three-dimensional lattice rotation consistently onto the undeformed configuration throughout deformation. This approach enables correlation analysis between initial microstructural heterogeneities and subsequent deformation quantities. Two distinct out-of-plane rotation modes are identified: dispersed intragranular rotations mediated by initial GNDs, and rigid-body rotations governed by soft-hard grain interactions. Statistically, initial GNDs suppress subsequent strain, lattice rotation, and dislocation accumulation. In addition, dislocation-based crystal plasticity finite element (CPFE) simulations demonstrate that precipitates at grain boundaries significantly enhance strain partitioning and rotation localization, especially for fine grains with strain and lattice rotation localization. Meanwhile, statistically stored dislocation (SSD) density is positively correlated with gains of strain and lattice rotation, whereas the evolution of GND density is locally independent with gain of strain. This framework enhances the understanding of deformation heterogeneity in AMed alloys and provides insights for microstructure-mediated optimization of mechanical properties.