Crack-free laser-based powder bed fusion of nickel-based alloys by intrinsic heat treatment
Considering the current increasing challenges in the field of climate-neutral energy supply as well as more efficient mobility in aerospace, the research of novel manufacturing processes and materials is of great importance. With the PBF-LB/M process (Laser-based Powder Bed Fusion of Metals) highly complex parts can be produced even now. In general, all weldable alloys can be manufactured using PBF-LB/M. Even some difficult-to-machine materials such as nickel-based alloys can be processed using PBF-LB/M, which leads to major advantages for the energy and space sector where these materials are favored due to their good mechanical properties at high temperatures. Nevertheless, one attractive candidate in terms of service temperatures (up to 800 °C) Inconel 738 (IN738) belongs to the category of hard-to-weld materials since this alloy tends to hot cracking. Concepts to manufacture IN738 with PBF-LB/P described in the literature can be separated into local changes the energy input and global preheating. Using pulsed exposure and thus a local change of energy input increased the probability of lack of fusion defects. Global preheating of the building platform up to 1000 °C is not resource efficient and not applicable for large components.
The aim of the ROBUST project is to fundamentally understand the thermal conditions which lead to cracking and locally change the thermal budget during processing to finally produce complex crack-free parts out of IN738. The ROBUST approach to process IN738 with PBF-LB/M is to locally preheat or rather postheat the material using the same laser as for melting and to reduce the thermal gradient, which decreases the cracking probability. Thus, the intensity distribution of the laser beam in the processing plane is changed via different ring-core distributions to tailor the thermal budget. This in-situ heat treatment will lead to dense and crack-free complex parts for novel applications, which will be proven on a demonstrator. Compared to the other concepts described, the ROBUST approach promises to be resource-saving and still lead to crack-free and dense components.