Laser direct energy deposition – the effect of process parameters on inconel 718

Laser Direct Energy Deposition (DED-L) is an Additive Manufacturing process which uses a laser beam as an energy source to melt blown metal powder to fabricate components. Complex relationships exist between the process parameters, which means that understanding these relationships, and their effect, is critical in understanding DED-L. This research investigates DED-L process parameters using a Trumpf 505 DMD system, aiming to determine the effect of altering specific process parameters on the metallurgical and mechanical properties of Inconel 718. Laser power, scan speed, and powder feed rate were first investigated using a Taguchi Design of Experiments. Anisotropy, build direction and a heat-treatment were then examined. The results demonstrate that the interactions between laser power, scan speed, and powder feed rate must be considered when determining process parameter values. An empirical working envelope of process parameter combinations for fabricating Inconel 718 on the Trumpf 505 DMD system was identified. For thick wall DED-L parts, changing the process parameters did not have any significant effect on the material properties. Process parameter combinations were found to be non-transferable between geometries – identical process parameters result in different material properties moving between different geometries. Thus individually built small test samples should not be used as representative of a larger components material properties. Combining different build directions did not have a negative effect on material properties at the interface between the build directions. Heat-treating eliminated the columnar dendritic grain structure, reduced Laves phase volume, and increased Vickers Hardness by 55%. This research adds to previous knowledge of how Inconel 718 behaves following fabrication by DED-L, and aids in understanding material integrity in thick wall DED-L builds. This contributes to improving the viability of using DED-L within industry.