Effect of off-axis laser incidence on residual stress in laser-based directed energy deposition of 316L stainless steel

Residual stress limits dimensional accuracy and service performance in the Laser-based Directed Energy Deposition (DED-LB) of 316L stainless steel. Process-integrated mitigation was demonstrated using off-axis (oblique-incidence) laser delivery. A 20 mm-thick multilayer build was characterized by neutron diffraction, neutron tomography, electron backscatter diffraction (EBSD), and Vickers macrohardness mapping. Residual stresses were confined to ±100 MPa, with interior tension and surface-adjacent compression; neutron tomography measured ∼0.001% porosity for pores ≥50 μm. Hardness of 150–230 HV20 colocated with compressive zones, and EBSD showed elongated columnar grains with position-dependent texture. The reduced stress state is attributed to the enlarged projected footprint and lower peak irradiance of off-axis delivery, which spread heat laterally, reduce the thermal gradient (G) and cooling rate (T˙), and favor conduction-mode melting. These results establish off-axis DED-LB as a route to in situ residual-stress control and microstructural tailoring while maintaining negligible resolved porosity in additively manufactured 316L components. The bulk, through-thickness maps and datasets provide component-scale validation to calibrate models and support process qualification.