Strain Monitoring During Laser Metal Deposition of Inconel 718 by Neutron Diffraction

In this study, we provide novel in situ monitoring of strain during laser metal deposition of Inconel 718 by neutron diffraction. Thermal, phase and stress-related contributions to the lattice parameter evolution are addressed for the representative regions during processing: melt pool, near melt pool, and far-field. The evolution showed a strong dependency on the build height and distance to the melt pool, i.e., time and temperature gradient, as expected. The different regions of interest reached at different moments the processing stable regime, which is contrasted with microstructural characterization. A homogeneous microstructure of coarse epitaxial dendrites and Laves phase was found from the third printed layer on, with fine globular delta phase precipitation at the grain boundaries. In comparison, neutron diffraction strain monitoring highlighted an offset of process stabilization after 24 layers for the melt pool and near-melt pool regions.