Metal Additive Manufacturing Conference - MAMC 2023

The processing by Laser powder bed fusion of non-weldable gamma’-strengthened Ni-based superalloys is recognized as challenging, especially due to hot cracking and liquation cracking mechanisms that occur during the solidification and the early cooling stages of the alloys.
The current study, which is based on activities carried out within the Horizon 2020 joint research project CUSTODIAN (grant agreement number 825103), offers an insight into the solidification mechanisms of the two CM247LC and IN713LC alloys, identifying the pre-heating temperatures which can mitigate cracking phenomena during LPBF processing. In particular, investigations on single track remelting showed that hot cracks could still form even after preheating at around 900°C, which shows gamma’ precipitation and segregation of carbide-former elements at the cell boundaries according to both microstructure observations and thermodynamic calculations. To acquire a better understanding about the ability of implementing extensive preheating to industrial AM processing, a numerical simulation tool was developed, simulating the effects of a dual beam laser system, capable of dynamic beam shaping. The output of the numerical model was first validated against experimental results of single-track scans. Then, further development was conducted to find optimal combinations for the shape, size, and power distribution of primary and secondary beams, in order to reduce the cooling rates in certain critical temperature ranges of the solidification and cooling process, to mitigate solidification cracking of these critical gamma’-strengthened Ni-based superalloys.