Heated liquid assisted in-situ preheating/heat dissipation synergistic low-stress laser directed energy deposition: microstructure and performance study on 316L stainless steel

Residual stresses inherent in laser directed energy deposition (L-DED) additively manufactured metals are tempting to trigger distortions or even cracks if their levels exceed the materials' yield strength, particularly for thin-walled components with large dimensions. In addition, the complicated thermal history induced by continuous heat input results in heterogeneous microstructures. Herein, a hot pool synergistic method was demonstrated, which is capable of alleviating residual stress and tuning the microstructure in L-DED. By immersing the building part layer-by-layer into heated inert liquid metal, printing on the exposed surface and in-situ preheating/heat dissipation/heat treatment for the immersed part are conducted synchronously at elevated temperatures to reduce the temperature gradient and tailor the texture. As a result, 316L stainless steel parts with less deformation and a homogeneous microstructure are manufactured. The experimental results systematically illustrate that the hot pool synergy is beneficial to the microstructure homogeneity, strength, hardness, wear, and corrosion resistance. This novel method provides a distinct way into the tunability of L-DED in residual stress, microstructure, and performance under extreme manufacturing conditions.