Ni-base superalloys are frequently used for cast components in the aero-engine and power generation industries. For joining and repair of these components, beam welding is often the method of choice in industrial praxis. However, precipitation-strengthened nickel alloys generally present poor weldability as a consequence of their high weld cracking susceptibility, with high segregating alloys like Mar-M247 even being considered unweldable. Therefore, strong efforts are taken on optimizing techniques and parameters to reduce crack formation during welding of these alloys. Optimization of welding parameters can be assisted by virtual modelling methods through different scales. To be able to focus onto the factors which eventually are responsible for crack formation during welding, comprehensive modelling of the whole process chain is required, starting from a realistic model of the base material and a simulation of the heat source on the macro-scale, and including melting and microstructure formation during welding on the micro-scale. Then, based on the thermal history and the exact microstructure, cracking susceptibilities during solidification can be deduced by hot cracking models adapted to the specific conditions. In this paper, results of microstructure simulations are presented for the technical superalloy MAR-M247 using the phase-field software MICRESS with coupling to Calphad databases. Based on prior phase-field simulations of equiaxed and columnar microstructures of the base material as well as results of a macroscopic simulation of the heat source, melting and subsequent solidification of MAR-M247 has been simulated for two different welding parameter sets. As-weld microstructures are compared to experimental welds, and the virtual hot cracking susceptibility, obtained from the simulation results using a modified Rappaz–Drezet–Gremaud (RDG) hot cracking criterion, is discussed against experimental crack observations.

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Conventionally cast Alloy 247 LC is characterized by good creep rupture strength and corrosion resistance at high temperatures and is therefore frequently used for cast components in the aero-engine and power generation industries. From a welding technology point of view, the precipitation- hardening nickel-based alloy has an increased susceptibility to hot cracking. Due to its high segregation tendency and its γ’ precipitation formation, the material is even classified as non-weldable. However, electron beam welding in a vacuum as the method of choice for joining and repairing nickel-based components in industrial practice, provides a variable beam welding process with high energy density. This allows varied temperature gradients to be implemented. In this paper, results of welding parameter optimization with regard to hot crack reduction are presented. For this purpose, a comprehensive crack analysis was carried out using scanning electron microscopy, metallography and X-ray microtomography and was then compared with the temperature gradient along the fusion line. Two hot cracking phenomena were identified and differentiated. Thereby, a clear dependence between temperature gradient and crack reduction becomes obvious.