The fractography analysis of IN718 alloy after three-point flexure fatigue test

Abstract

In this study, the high cycle fatigue (HCF) properties of IN718 superalloy with given chemical composition were investigated at three-point flexure fatigue test at room temperature. INCONEL alloy 718 is nickel-chromium-iron hardenable alloy and due to its unique combination of mechanical properties (high-strength; corrosion-resistant and so on) used for production of heat resistant parts of aero jet engine mostly. Mechanical properties of this alloy are strongly dependent on microstructure and on presence of structural features such are principal strengthening phase gamma double prime, gamma prime and due to its morphology less desired delta phases. The mentioned phases precipitate at various temperature ranges and Nb content as well. The three-point flexure fatigue test was performed on ZWICK/ROELL Amsler 150 HFP 5100 test equipment with approximate loading frequency f=150 Hz. The S – N (Stress – Number of cycles) curve was obtained after testing. With the help of scanning electron microscope (SEM), fractography analyses were performed to disclose the fracture features of specimens in different life ranges. The brief comparison of three-point flexure and push-pull fatigue loading modes and its influence on fatigue life is discussed as well.

Keywords

• IN 718 alloy
• low frequency fatigue loading
• three-point flexure
• fatigue crack initiation
• fatigue crack propagation
• S–N curve
• SEM observing
• fractography analysis