Effect of a Surface Element Exposure Algorithm for Selective Laser Melting on the Mechanical Properties of the Synthesized Material: II. Fatigue

Using a high-strength VZh159 nickel superalloy as an example, we study the low-cycle fatigue characteristics of cylindrical solid and hollow specimens synthesized by selective laser melting (SLM). Specimens with a gage portion surface roughness of R_a = 4.80 μm after SLM, R_a = 1.06 μm after vibratory finishing, and R_a = 0.20 μm after polishing are analyzed. A negative effect of the surface roughness on fatigue life has been established: the fatigue life of vibration-finished and unprocessed specimens turns out to be lower than that of polished specimens by 17%. The Manson–Coffin and Ramberg–Osgood curves indicate increased plasticity of specimens with an unprocessed surface and surface hardening after vibratory finishing. The results of fractographic studies demonstrate that the decrease in the fatigue strength is associated with the presence of defects caused by the peculiarities of exposure of surface elements, and this decrease in hollow specimens is greater.