Ultrahigh Cycle Fatigue Performance of GH4169 Alloy by Selective Laser Melting

Tensile test and high/ultrahigh cycle fatigue tests with 10⁵-10⁹ cycles were carried out on selective laser melting (SLM) formed GH4169 alloy; the alloy was heat treated standardly. The tensile properties, fatigue properties and fracture morphology were studied, and the fatigue fracture mechanism was analyzed. The results show that after heat treatment, the tensile strength and yield strength of SLM formed GH4169 alloy were higher than those of forgings, but the elongation was greatly reduced, and the elastic modulus was slightly reduced. The S-N curve of SLM formed GH4169 alloy presented a stepped shape, showing inflection points near the 4×10⁵ cycles and 5×10⁷ cycles. The cracks of specimens in the high-cycle fatigue interval of 10⁵-10⁷ cycles all originated on the surface, while those in the ultrahigh cycle fatigue life interval exceeding 10⁷ cycles were mostly generated inside. The internal crack source was the circular keyhole produced by the high laser energy density, and the residual carbide in the hole accelerated the crack initiation and reduced the fatigue life.