Unexpected mechanical behavior of directed laser deposited Inconel 718 caused by titanium nitride

다국어 초록 (Multilingual Abstract)

In this work, the effects of titanium nitride (TiN) inclusions on the mechanical properties of Inconel 718 (IN 718) deposited with directed laser deposition (DLD) was studied. The grain morphology of DLD-processed IN 718 showed evident anisotropy depending on the direction which applied the DLD processing method. However, the anisotropy of mechanical properties not only showed a completely different tendency at room temperature and 700℃, but also exhibited a different tendency from previous studies at 700℃. Tensile tests were performed to compare the mechanical properties of the DLD-processed and conventionally cast, and heat-treated IN 718. They exhibit different mechanical properties. These results suggest that factors except for grain morphology influence the mechanical properties of DLD-processed IN 718, which is presented as TiN inclusions in this study. Strain mapping, fractography, and X-ray tomography analyses were performed and showed that transgranular micro-cracks exist inside the TiN inclusions, propagate faster than the matrix, and cause strain concentration in the TiN inclusions. This means that TiN inclusions affect the anisotropy in mechanical properties at high-temperature.