EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

L-PBF, for Laser Powder Bed Fusion, is an additive manufacturing process, which consists in successively melting layers of powdered material with a laser. The process features very short interactions between the raw material (powder) and the laser, resulting in very high solidification and cooling rates. As a result, the generated microstructures are usually far from equilibrium. During thermal cycling in manufacturing by L-PBF process, phase precipitation and thermal strain hardening occur concomitantly, leading to high dislocation density correlated with anchoring to precipitates. It is therefore important to understand and control precipitation kinetics with respect to the thermal strain hardening phenomena generated by the thermal cycles of the L-PBF process. The families of alloys concerned by this issue are nickel-based superalloys and aluminum alloys.
The aim of this study is to understand the thermal, metallurgical and mechanical phenomena generated during the manufacture of nickel-based superalloys and aluminum alloys by LPFB, in order to evaluate the impact of thermal strain hardening on the precipitation of the strenghtening phases and to be able to propose an optimized post-manufacturing heat treatment.
Hardness measurements on as-fabricated as well as on heat-treated samples give access to the evolution of the residual stresses of the LPBF microstructures. A fine characterization of the as-built microstructures and subsequent to various heat treatments using scanning electron microscopy and transmission electron microscopy show the interaction between dislocation density and precipitation for the two considered alloys families.