Tensile behaviour and microstructure of wire-based laser directed energy deposited normal- and high-strength steels

Wire-based laser-directed energy deposition, referred to as DED-LB or WLAM, is an emerging additive method using laser-melted wire feedstock, offering high deposition rate, smooth surfaces, and high precision. These capabilities indicate strong potential for construction, particularly for complex and optimised components, yet structural adoption necessitates in-depth assessments of mechanical and microstructural properties. This study describes a detailed experimental study into the mechanical behaviour and microstructural characteristics of ER70S-6 normal-strength and ER110S-G high-strength steels produced by DED-LB, with focus on property variability and orientation-induced anisotropy, compared with wire-based arc directed energy deposition (i.e., DED-Arc or WAAM). Tensile tests are performed on as-built specimens extracted from various orientations, with 3D scanning quantifying surface undulations, and digital image correlation recording full-field strains. The microstructures are characterised using optical and scanning electron microscopy and electron backscatter diffraction, and microhardness is mapped to microstructural phases. The results show that both steels show favourable stiffness properties and ductility with modest orientation-dependent anisotropy, where ultimate strength ratios across orientations are 0.95-1.00, and elongation ratios are 0.94-1.06. Most coefficients of variation for tensile strength and fracture elongation are found to be below 0.07, comparable to conventional steels. Dominant microstructural phases are shown to be uniformly distributed, with observed layer boundary regions in agreement with local microhardness. Relative to DED-Arc, DED-LB steels, especially for the high-strength grade, are shown to exhibit higher ductility with reduced orientation sensitivity while maintaining comparable strengths. Overall, the findings provide as-built dataset for informing wire-based process assessment and selection for civil engineering applications.