Abstract: Superalloys with high Al + Ti contents (≥ 6 wt. %) exhibit pronounced susceptibility to hot cracks, significantly limiting their applicability in additive manufacturing. In this study, we propose an innovative interlayer micro-forging (MF) integrated directed energy deposition (DED) hybrid process, which successfully fabricates crack-free K447A deposits featuring an alternating columnar-equiaxed grain microstructure. The results demonstrated that the MF process significantly reduced the content of low-melting-point eutectic, thereby suppressing liquation crack susceptibility. The MF deformed columnar grain surface layer promoted the formation of equiaxed grains at the molten pool bottom, interrupting epitaxial growth and consequently reducing the solidification cracks susceptibility. The MF process transformed tensile residual stresses into compressive stresses within the deposits. Under thermal activation, the highly strained deformation layers underwent static recrystallization, primarily nucleated through sub-grain rotation and twin termination high-energy interfaces. Compared to conventionally deposited K447A, the hybrid processed deposits with alternating grain structures exhibited simultaneous enhancements in strength and ductility, alongside markedly reduced anisotropy, improving the material's resistance to ductility-dip cracks. Specifically, horizontal tensile strength and elongation increased by 28.4 % and 403.6 %, respectively, while the elongation anisotropy index decreased from 70.4 % to 14.3 %. This study validates the efficacy of the DED+MF hybrid process in suppressing hot cracks and enhancing mechanical properties, underscoring its broad applicability for the additive manufacturing of superalloys with high Al + Ti content.

Key words: Non-weldable superalloy, Direct energy deposition, Micro-forging, Static recrystallization, Hot cracking