Fatigue Behavior of Laser Beam Directed Energy Deposited Inconel 718 at Elevated Temperature

Nickle based super alloys such as Inconel 718 are being extensively used to manufacture turbine blades for jet engines due to their superior mechanical properties at higher working temperatures. Furthermore, poor machinability associated with Inconel 718 also makes it an attractive material for additive manufacturing processes, which possess the capability to fabricate near net shaped parts. Hence, in this study, the fatigue behavior of Inconel 718 fabricated using laser beam directed energy deposition (LB-DED) is investigated under strain-controlled, fully-reversed conditions at an elevated temperature of 650° C. Fractography analysis was conducted to determine the failure mechanism for additive manufactured Inconel 718 due to higher working temperatures. The results obtained from the fatigue and fractography analysis were then compared with the results obtained from fatigue tests conducted at room temperature. At elevated test temperature, LB-DED Inconel 718 specimens exhibited lower fatigue resistance compared to the tests conducted at the room temperature, primarily in the low cycle fatigue regime. Whereas, in the high cycle fatigue regime the effect of test temperature was observed to be minimal. Furthermore, secondary cracks resulting from the formation of brittle behaving precipitates on the grain boundaries was also evident from the fractography analysis indicating significant changes in the microstructural features of LB-DED Inconel 718 as a consequence of elevated test temperature.Mechanical Engineerin