Tsinghua University Professor Lin Feng's Team: Liquid Metal-Assisted Process Enables Efficient and Sustainable 3D Printing Manufacturing with Optimized Material Properties

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November 5, 2025 Materials 3573

△ Fig. 1 Working principle of the conventional additive manufacturing powder bed.

I. Research Snapshot

Laser Powder Bed Fusion (LPBF) is a mainstream metal 3D printing process, but it relies on a solid powder bed. This means the subsequently spread upper powder layers are entirely supported by the previously spread lower powder layers and the build platform (Fig. 1). The drawback is the need for a large amount of powder to fill the build cylinder to form the powder bed. Although unconsumed powder can be recycled and reused, several structural limitations exist:

Low powder utilization during the forming process, resulting in extremely high material costs that hinder the scaling of powder bed additive manufacturing technology and its large-scale application.

Large interlayer thermal gradients, leading to residual stress concentration and cracking.

Poor thermal conductivity of traditional powder beds, making microstructure control difficult.

How to improve powder utilization during forming to achieve low-cost and efficient additive manufacturing, and further leverage the forming process for precise control of material microstructure, have been core challenges in this field. Professor Lin Feng's team from the Department of Mechanical Engineering at Tsinghua University has pioneered the Liquid Metal-Assisted Laser Powder Bed Fusion (LMA-LPBF, Fig. 2) technology. This technology utilizes the low melting point and high boiling point physical properties of liquid metal tin to optimize the thermal management process of additive manufacturing, creating a dynamic printing environment with "liquid-solid synergy," and revealing the intrinsic mechanisms linking thermal management, microstructure evolution, and performance optimization. It not only theoretically expands the paradigm of thermal field control in additive manufacturing but also provides novel solutions for large components, functionally graded materials, and multi-metal composite printing in industrial applications. It addresses the long-standing "solidification constraints" of traditional LPBF technology, opening a new path for 3D printing high-performance metal materials.

The related research was published in the authoritative international journal International Journal of Machine Tools and Manufacture (IF: 18.8), titled "A novel in-situ field-assisted powder bed laser fusion using liquid metal enabling microstructure control and strength enhancement of austenitic steel". The first authors are Assistant Researcher Liang Xiaoyu from Tsinghua University's Department of Mechanical Engineering and Ph.D. student Wang Yurong from Sichuan University. The corresponding author is Professor Lin Feng from Tsinghua University's Department of Mechanical Engineering. Other authors include Associate Researcher Zhang Lei of Tsinghua University; Tsinghua Master's graduates Liu Wei (Class of '24) and Sun Yizhuo (Class of '24); Master's student Xiao Buwei (Class of '23); Ph.D. student Liu Qingze (Class of '25); Professor Peng Huabei from Sichuan University; Assistant Professor Zhou Jun from Guangxi University; and Master's graduate Lü Pengcheng (Class of '25) from Guangxi University, among other collaborators. This research was supported by the National Natural Science Foundation of China's Original Exploration Program and its continuation project.

Paper link: https://doi.org/10.1016/j.ijmachtools.2025.104334

△ Fig. 2 Schematic diagram of the LMA-LPBF forming process is shown in (a–c), surrounded by the red dashed box. During the LMA-LPBF forming process: (a) As the part height increases, the build platform descends layer by layer; (b) The powder recoater spreads a new layer of powder on the surface; (c) The laser melts the designated areas. This cycle continues until the part is fully formed. A fundamental requirement for successful manufacturing is that both the platform movement and powder spreading process must not compromise the integrity and flatness of the powder bed floating on the liquid metal (a). Furthermore, the excellent surface tension of the liquid metal stably supports the powder bed (b), enabling a cost-effective manufacturing route. Notably, the exceptional thermal conductivity of the liquid metal allows for more precise control of microstructure evolution during solidification (c), thereby creating possibilities for tailoring material properties.

II. Core Innovation: Making "Metal Powder Float" on Liquid Metal

The Liquid Metal-Assisted Laser Powder Bed Fusion technology uses liquid metal to replace the solid powder bed, constructing a "liquid-floated printing platform":

Liquid tin is selected as the highly thermally conductive supporting medium.

Metal powder stably floats on the liquid metal surface due to surface tension.

A dynamic thermal field of "local liquid surface - solidification interface" forms in the laser melting zone, achieving rapid energy conduction and uniform distribution.

This unique design offers significant advantages:

Powder consumption is reduced by approximately 50%.

Cooling rates and solidification gradients are controllable, suppressing residual stress.

Grain refinement and texture optimization achieve a better balance of strength and ductility.

A thermal management strategy for the forming process is realized, which is repeatable and scalable for additive manufacturing equipment.

III. Academic and Engineering Significance: Liquid Metal Thermal Management Reshapes the 3D Printing Process

Innovative Process Concept
Unlike traditional powder-bed-based additive manufacturing methods, LMA-LPBF technology replaces the solid powder bed with a thin powder layer floating on a liquid metal surface, achieving precise control of the thermal field and forming environment. This significantly reduces powder consumption and provides a new approach for efficient and sustainable metal additive manufacturing.

Balancing Manufacturing Efficiency and Sustainability
The high thermal conductivity and liquid support characteristics of LMA-LPBF make the forming process more stable and energy-efficient. It reduces manufacturing costs while ensuring structural strength, meeting the urgent needs of future industry for resource utilization and sustainable manufacturing.

New Paradigm for Designable Microstructures
This research demonstrates the potential of using liquid metal to control grain size, precipitation behavior, and dislocation strengthening mechanisms, pointing towards a development direction of programmable material microstructures and providing a new technical path for precisely designing material properties.

Broad Applicability Across Material Systems
The revealed liquid-solid synergistic thermal control mechanism has universal significance and can be extended to fields such as aerospace, automotive, and biomedical materials, which have extremely high requirements for balancing strength and toughness.

IV. Key Results: Dual Control of Microstructure and Properties

Experimental results show that austenitic stainless steel prepared using LMA-LPBF achieves breakthroughs in microstructure and mechanical properties:

The thermal management capability provided by the liquid tin enables the laser not only to refine grains but also to control the size of the fine-grained zones.

Fig. 3 (a) EBSD image of a horizontal cross-section shows the LMA-L-PBF technology can control heterogeneous structures under different normalized equivalent energy density (E₀) values. The E₀ value influences the size of the fine-grained zone: insufficient heat input activates heterogeneous nucleation of the material, while excessive heat input leads to grain growth. (b) Average grain size distribution corresponding to different E₀ values. (c) Trends of high-angle grain boundary proportion and KAM value with changing E₀.**

The rapid cooling process significantly increases the nucleation rate within the austenitic steel.

Fig. 4 (a) Transmission electron microscopy image and corresponding (g1-g10) energy-dispersive X-ray spectroscopy maps showing segregation of Cr, Mo, Nb, O, Ti, Mn, and Si elements to the solidification cell walls. High-resolution transmission electron microscopy images show the nano-precipitates are: (b) MnSiO₃ and (c) TiO₂. (d) Dark-field transmission electron microscopy image indicates that the cell boundaries in MA-ASS are modified by high-density nano-phases. (e) Enlarged view of precipitates along the dislocation cell walls. (f) Schematic diagram of the "hammer-chain" structure formed by precipitates and dislocations.

The formed heterogeneous austenitic steel achieves a yield strength exceeding 1.1 GPa, a tensile strength of 1.5 GPa, while maintaining an average uniform elongation of 7%.

Fig. 5 (a) Tensile engineering stress-strain curves of MA-ASS compared with 316L stainless steel; (b) True stress-strain curves of specimens prepared by Laser Powder Bed Fusion (L-PBF) and Liquid Metal-Assisted Laser Powder Bed Fusion (LMA-LPBF) processes, respectively; (c) Corresponding strain hardening rate vs. true strain relationships; (d) Summary comparison of ultimate tensile strength and uniform elongation for additively manufactured 316L stainless steel, including data from this study, Laser Powder Bed Fusion (L-PBF), Directed Energy Deposition (DED), and Electron Beam Powder Bed Fusion (EB-PBF) processes.