Thermal-field engineering in metal additive manufacturing via liquid-metal-assisted laser powder bed fusion

Laser powder bed fusion (L-PBF) enables the fabrication of complex metallic components but offers limited control over the highly localized and non-equilibrium thermal histories that govern solidification, phase transformation, defect evolution, and residual stress development. Here, we develop a liquid-metal-assisted laser powder bed fusion (LMA-LPBF) strategy that employs liquid Sn as a dynamic heat-transfer medium to reconfigure the thermal boundary conditions during additive manufacturing, enabling in-situ thermal-field engineering and microstructure control. The effectiveness of this strategy is demonstrated in austenitic stainless steel, IN718 superalloy, and Ti–6Al–4V alloy. In austenitic steel, enhanced heat extraction promotes grain refinement and heterogeneous microstructure formation, leading to a yield strength above 1.1 GPa. In IN718, thermal-field regulation refines grains, suppresses detrimental Laves-phase formation, reduces residual stress, and enables a favorable strength–ductility combination. By further integrating in-situ laser remelting, gradient heterogeneous surface layers can be constructed for site-specific strengthening of complex thin-walled structures, accompanied by substantially enhanced hardness and reduced tensile residual stress. More fundamentally, thermal-field engineering enables control beyond solidification. In Ti–6Al–4V, the engineered thermal environment regulates the β→α transformation and defect evolution, producing a hierarchical nonequilibrium architecture composed of refined α laths, nanotwins, retained β phase, and multiscale interfaces. This architecture promotes dislocation storage, strain partitioning, and back-stress hardening, enabling a strength of approximately 1.2 GPa together with an elongation of about 17%. These results establish liquid-metal-enabled thermal-field engineering as a versatile route for manipulating solidification, phase transformation, defect architecture, and spatially resolved properties during additive manufacturing, providing new opportunities for the integrated design of high-performance metallic materials and components.

Xiaoyu LIANG is currently a Research Assistant Professor in Department of Mechanical Engineering of Tsinghua University.

His main research directions include powder bed fusion additive manufacturing equipment and processes, numerical modeling simulation of additive manufacturing, and service performance of additive manufactured metals.

He conducted the Youth Scientist Project of the National Key R&D Program, and participated in projects such as "Aircraft Engines and Gas Turbines Special Project" and “Defense Industrial R&D Project". He published over twenty papers as the first author or corresponding author in journals such as International Journal of Machine Tools and Manufacture, Additive Manufacturing.