Creep property of Inconel 718 superalloy produced by selective laser melting compared to forging

Creep property and microstructure evolution of Ni-base superalloy Inconel 718 fabricated by selective laser melting (SLM) are compared to that of the forged material. Creep tests have been carried out with standard tensile specimens at 700 degrees C and 560 MPa. Scanning electron microscopy (SEM), electron backscattered diffraction (EBSD) and transmission electron microscopy (TEM) were used to investigate the microstructural evolution in both specimens after creep exposure. The SLM Inconel 718 shows poorer creep resistance and plasticity compared to the forged Inconel 718, which is associated with the microstructure in the samples of two different manufacturing processes. It is found that the SLM Inconel 718 samples have large columnar grain structure, delta phases continuously distribute at grain boundaries, and high residual stress, which leads to the initial microstructure instability during creep exposure. However, the forged Inconel 718 samples have fine equiaxed grain, more twin boundaries, micro-twin, gamma '' phase, and low residual stress before creep, which results in a low steady creep rate and excellent plastic property. Based on these results, several suggestions were provided to improve creep resistance and plasticity of SLM Inconel 718.