Weld Cracking in Precipitation Hardening Ni-based Superalloys

Manufacturing of hot structural components for aero engines requires the materials being used to beweldable. The high demands on strength and temperature resistance make nickel based superalloys thematerial of choice for this application. Alloy 718 has been the standard grade for several years,providing high strength at elevated temperatures while being weldable due to the relatively slowprecipitation kinetics of its hardening phase gamma double prime. Increasing operating temperaturesas well as intermittent cycling of land-based gas and steam turbines motivate research on highlytemperature stable alloys such as nickel based superalloys. Increased temperature stability ofprecipitation hardening superalloys is generally achieved via the gamma prime phase, which incontrast to gamma double prime causes a very rapid hardening effect in the material.Rapid hardening of the gamma prime phase can cause strain age cracking (SAC), a crackingphenomenon occurring during heating towards the post weld heat treatment when stress relaxationmechanism coincide with the precipitation of hardening phases. With the general mechanism of SACbeing established, detailed knowledge about the material response is necessary to be able to predict thewelding behaviour and to prevent SAC. This is especially relevant with regard to newly developedalloys such as Haynes\uae 282\uae, where limited weldability data is available. This work hence sets focuson investigating the weldability of the relatively new superalloy Haynes\uae 282\uae.It was found that the welding response of Haynes\uae 282\uae is generally good, with the heat input duringwelding being identified as main effect on the cracking response under the studied conditions.Solidification cracks were observed in the material, while neither heat affected zone liquation cracksnor SAC could be confirmed. A simulative Gleeble test was developed to provide more data onductility in the SAC temperature range and its dependence on ongoing precipitation reactions duringthermal exposure, correlating the loss in ductility with hardness evolution in the material