Study of the Microstructures and Fatigue–Creep Properties of a Laser-Directed Energy Deposition Epitaxial Ni-Based Superalloy

In recent decades, laser-directed energy deposition (LDED) has become one of the most promising techniques for additive manufacturing. In this work, LDED technology was employed to prepare thin-walled nickel (Ni)-based superalloys. The microstructures of epitaxial Ni-based superalloys were investigated via a series of characterization techniques. The results revealed that the constantly increasing number of microdefects clustered together during the LDED process to transform low-angle grain boundaries into high-angle grain boundaries, resulting in the formation of stray grains. Moreover, finite element simulations of the LDED process were carried out to analyze the transient temperature field and stress field during and after deposition, respectively. The maximal residual tensile stress occurred at the epitaxy/stray grain interface. The experimental results revealed that the fatigue–creep life of the repaired sample was shorter than that of the as-prepared sample, especially under higher loads. In addition, the as-prepared sample fractured in the direction of 45° due to crystallographic slipping, whereas the failure of the repaired sample occurred at the epitaxy/stray grain interface due to a higher defect density and greater residual tensile stress.