Improved strength properties of LPBF Inconel 718 through process optimization and thermomechanical treatment

Kurzfassung

The use of LPBF in the aerospace sector promises significant advantages from manufacturing complex and integrated parts such as turbine blades or combustion chambers with an internal network of cooling channels [1]. However, the limits of the component geometries that can be achieved economically as well as the LPBF materials properties still pose sizable challenges. Despite the large number of studies carried out to date, further research is required to unravel the correlation between process parameters, subsequent heat treatments and the resulting mechanical and microstructural properties. The LPBF solidification process determines the microstructure and texture and has a complex dependence on the laser parameters, which, if not optimized carefully, can lead to unexpected loss of alloying elements, high residual stresses, cracking and other defects. In this study, the effects of the LPBF process parameters and subsequent heat treatments on the resulting mechanical and microstructural properties of Inconel 718 will be presented. The parameters were optimized and a suitable heat treatment designed to improve the properties of the material by adapting its microstructure and reducing the formation of Laves- or Delta-phase precipitates. Orientation effects due to texture or layered non-fusion defects were considered for mechanical characterization using tensile specimens. Different heat treatment conditions including double ageing and HIP were studied and mechanical properties correlated with the corresponding microstructures and phase compositions, which have been quantified by high-energy x-ray diffraction. The strategy for achieving an optimal strength-ductility trade-off in LPBF IN718 will be discussed.