Effect of hot isostatic pressure on the microstructure and tensile properties of γ′-strengthened superalloy fabricated through induction-assisted directed energy deposition

The microstructure characteristics and strengthening mechanism of Inconel738LC (IN-738LC) alloy prepared by using induction-assisted directed energy deposition (IDED) were elucidated through the investigation of samples subjected to IDED under 1050 degrees C preheating with and without hot isostatic pressing (HIP, 1190 degrees C, 105 MPa, and 3 h). Results show that the as-deposited sample mainly consisted of epitaxial columnar crystals and inhomogeneously distributed gamma ' phases in interdendritic and dendritic core regions. After HIP, grain morphology changed negligibly, whereas the size of the gamma ' phase became increasingly even. After further heat treatment (HT, 1070 degrees C, 2 h + 845 degrees C, 24 h), the gamma ' phase in the as-deposited and HIPed samples presented a bimodal size distribution, whereas that in the as-deposited sample showed a size that remained uneven. The comparison of tensile properties revealed that the tensile strength and uniform elongation of the HIP + HTed sample increased by 5% and 46%, respectively, due to the synergistic deformation of bimodal gamma ' phases, especially large cubic gamma ' phases. Finally, the relationship between phase transformations and plastic deformations in the IDEDed sample was discussed on the basis of generalized stability theory in terms of the trade-off between thermodynamics and kinetics.