Effect of heat treatment temperature on the microstructural evolution of CM247LC superalloy by laser powder bed fusion

To attain the desired mechanical properties of an additively manufactured component, robust post-processing in term of thermal treatment is highly required to reduce the crystallographic anisotropy. However, the microstructure appearance with respect to the post-treatment temperature is not well understood mechanistically. In this study, the microstructural evolution of grains of a laser-powder bed fused (L-PBF) nickel-base superalloy, CM247LC, during post-processing heat treatment is investigated systematically. Recrystallization barely happens below the gamma solvus temperature leading to a remaining unhomogenized dendritic(cellular) structure. However, recrystallization is introduced above the gamma solvus temperature. By considering the grain boundary (GB) migration mechanisms and supported by experimental observations, the sluggish recrystallization behavior of this gamma-strengthened nickel-based superalloy has been understood. Owing to lack of the difference in stored energy between adjacent grains, this primary driving force is constrained. The GB migration is majorly driven by capillarity force (1-10 MPa) before the recrystallization occurrence, which is evident by the evolution of GB curvatures. On the other hand, the Zener pinning force generated from GB precipitates including carbides and gamma precipitates provides the dragging force in the comparable scale (1-10 MPa) against the GB migration.Funding Agencies|Swedish Agency for Innovation Systems via SIP Metalliska Material, (Vinnova) [2018-00804]; Linkoping University (SFO-MAT-LiU) [2009-00971]; CAM2 the center for Additive Manufacture - Metal (Vinnova)Vinnova [201605175]</p