Design and optimization of fatigue life studies on induction hardened IN718 alloy for gas turbine applications

Abstract

The Inconel 718 (IN718) superalloy is commonly used as a component in industrial gas turbines due to its excellent corrosion resistance and high-temperature properties. Generally, gas turbines experience failure in their service on account of high thermal fatigue. In the present research, specimens of Inconel 718 superalloy are treated at two different temperatures 850℃ and 1000℃ (IHT1 & IHT2) with oil quenching, respectively. The specimens are studied with controlled strain amplitudes for different values 0.6%, 0.7% & 0.8% at room temperature and 800°C. It is noticed that the fatigue lifetimes of induction-hardened specimens are greater than those of untreated specimens at the above-mentioned strain amplitude values at room and elevated temperature, whereas the fatigue life of all the specimens reduces as strain amplitudes increase. Interestingly, the stress difference among the three strain amplitudes gradually decreases as the fatigue test progresses and induction-hardened specimens have cyclic softening behaviour as compared to untreated specimens’ cyclic hardening behaviour. Additionally, the mode of fracture for IN718 superalloys in the current study is entirely transgranular, as shown by the fracture surface observation using a scanning electron microscope (SEM).