Effects of sandblasting and HIP on very high cycle fatigue performance of SLM-fabricated IN718 superalloy

Additive manufacturing (AM) has a bright application prospect because of its ability to efficiently manufacture complex and precise parts. However, defects such as pores and surface roughness produced in the manufacturing process severely restrict its application. Here ultrasonic fatigue test is conducted to evaluate the effects of sandblasting and hot isostatic pressing (HIP) on the VHCF performance of IN718 fabricated by selective laser melting (SLM). X-ray computed tomography (CT) and a 3D-optical profiler are used to characterize the defects, including size and location. After sandblasting, the crack initiation sites transfer from surface to interior, which is attributed to the improved surface state. Kurtosis, rather than the often-employed arithmetical mean height, is used to evaluate the contribution of sandblasting on surface state due to its ability to characterize surface defect morphology. With the elimination of defects and the introduction of the compressive residual stress under the combination of sandblasting and HIP, the potential initiation sites are transferred from the locations of defects to the weak microstructure, which still significantly improves the fatigue resistance. The tensile test reveals that the VHCF performance was more sensitive to small defects than the tensile properties. Finally, the influence of defects on fracture behavior is analyzed in the framework of fracture mechanics.