Creep anisotropy in additively manufactured IN738LC: Grain boundary sliding and multiple deformation mechanisms in tension and compression

Insufficient understanding of the high-temperature microstructure-property relationships of additively manufactured (AMed) Ni-base alloys still hinders their safe and widespread application. In particular, the impact of the pronounced, process-induced defect population in AMed components, most notably grain boundaries arising from multiple sources, remains insufficiently quantified, introducing significant uncertainty in property predictions and lifetime assessments. In a previous study, we assessed creep anisotropy in AMed IN738LC tensile specimens [Mat. Sci. Eng. A 907 (2024) 146690] where the effects of Crystal Plasticity (CP) deformation mechanisms, specifically Superlattice Extrinsic Stacking Faults (SESF-related), and microstructural characteristics were studied. In the present study, we systematically investigate the anisotropic creep response in compressive creep tests of AMed IN738LC while extending our crystal-plasticity framework to explicitly incorporate grain-boundary sliding (GBS). By combining tensile and compressive results, the effect of multiple deformation mechanisms on the observed creep anisotropy is studied. Our results reveal that GBS is the primary deformation mechanism for the specimens with a loading axis tilted to the building direction. We demonstrate that the prediction accuracy of creep anisotropy significantly improves by accounting for GBS and the combined extrinsic and intrinsic stacking fault (SF) deformation mechanisms.