INCONEL 718 is one of the most widely used nickel based super alloys in aircraft engine components, as it offers high strength at elevated temperature and excellent creep resistance. Due to the sensitivity of the alloy to environmental influences such as fatigue and stress corrosion cracking, it is important to optimise material performance to ensure the safe operation of aircraft engines.
Currently, there are many different methods of manufacturing metal alloys using Additive Manufacturing (AM). AM offers great benefits such as reduced cost and time for production as well as improved design freedom. In addition, it allows manufacturers to produce complex shaped parts that cannot be produced by conventional manufacturing processes. Among these AM processes, Wire Arc Directed Energy Deposition (WAAM) is an attractive method as it offers the ability to deposit material layer-wise.
However, the microstructure of in718 deposited via WAAM can differ from the wrought material owing to the process. In particular, a greater amount of precipitation can be observed at the dendrite arms, which is often associated with a reduction in tensile and creep properties. Moreover, the formation of a Laves phase and other metal carbides may also affect mechanical properties at elevated temperature.
To address the issues with the microstructure and improve the in718 performance, a number of surface enhancement techniques were explored. Laser shock peening (LSP) was found to be an effective technique as it induced less cold work and thus a beneficial compressive residual stress in the in718 alloy at elevated temperatures.