Extremely rapid heating and cooling rates during the additive manufacturing (AM) process generate complicated thermal cycles, which affect the microstructure evolution and ultimate mechanical properties of the alloy. In this paper, FGH96 blocks with a height of 6 mm were prepared by selective laser melting (SLM) and the microstructure was characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Comparing specimens of varying heights, it was found that subsequent thermal cycles (STC) coarsened some solidified grains and accelerated the grain growth along the build direction, together with an increase in texture intensity and high-angle grain boundaries (HAGBs). After coarsening the grains in the middle portion of the built block, finer grains were observed near the top area due to a faster cooling rate. There were numerous dislocations in the grain because of the occurrence of unequal internal tension. In the middle of the sample with stable thermal cycles, the dislocations were both perpendicular to the grain growth direction and 45° off it. In spite of the texture characteristics, the segregation of elements was also found to be influenced by thermal cycling. Inherent reheating leads to the increase in the Laves phase and the decrease in the γ’ phase as subsequent deposition. This was also one of the reasons why the microhardness of the sample decreased as the building height and the other reason being the decrease in the solution treatment of the later sediments.

Inclusions are important phases affecting material properties in complicated ways. In this paper, a quantitative study of the addition of HfO₂ inclusions to DZ125 nickel-based superalloys was performed. Experimental results showed that the introduction of HfO₂ inclusions caused a loss of strength and ductility. The carbide morphology also changed significantly from skeletal-shaped to block-shaped, resulting in a remarkable discrepancy in the fracture behavior under quasi-in-situ tensile testing. The SEM dynamic observations showed that cracks were initiated from the skeletal carbides and almost failed to propagate into the matrix. In contrast, the damage behavior of block-shaped carbides also involved internal cracking but with a tendency to form interconnected microcracks during propagation. A crystal plasticity finite element model (CPFEM) method was further developed to study the stress/strain behavior during the deformation process, considering the crystal orientations and microstructure morphologies from the EBSD data. Those elastoplastic parameters were determined through nanoindentation experiments. Simulation results verified that blocky carbides produced a pronounced strain concentration at the interface of the carbides and matrix, thereby increasing the tendency of crack formation. This paper provides a fundamental understanding of the role of inclusions in material recycling applications.