Laser additive manufacturing (AM) has become one of the key technologies in the fabrication of components with high performance and complex structure, playing an important role in the fields of aeronautics, astronautics, weapons, etc. Based on the independently developed Alumics materials, professor Wang Haowei's group (School of Materials Science and Engineering, Shanghai Jiaotong University) focuses on the entire AM procedure of “materials & process & structure”. They constructed a design theory of powder compositions for AM, revealed the formation mechanism of key defects, established a multiscale method of defect controls and deformation controls during the printing, and realized the integrated design and forming of large, complex and functional structures. Relevant research achievements were published in top journals, such as Progress in Materials Science, International Journal of Machine Tools and Manufacture, Additive Manufacturing, and Composites Part B: Engineering, etc.
Due to the inherent fast heating and cooling process of AM, large columnar grains and periodic cracks usually appear in the solidified structure of the fabricated parts. It is recognized that nanoparticles can solve the problems mentioned above. Till now, most of the work on nanoparticle-reinforced metal matrix composites focuses on the microstructure and mechanical properties. The group established a comprehensive model, combining the multiphysics modelling with the single-track experiments, and quantified the effects of nanoparticles on the melt pool characteristics and printability. This work provides a theoretical framework to predict printability and efficiently screen for promising metal materials with good printability. The research results were published in the Additive Manufacturing (IF=11.632) under the title of “A comprehensive model to quantify the effects of additional nano-particles on the printability in laser powder bed fusion of aluminium alloy and composite”.
https://doi.org/10.1016/j.addma.2022.103011
The introduction of nanoparticles can improve the printability, refine the grain size and enhance the mechanical properties of non-castable 2024Al alloys. However, there is limited research related to the efficiency of these inoculates. The key challenge is quantifying the relationship between nanoparticle content and defect content, grain refinement level, and mechanical properties of the printed materials. Thus, the group, together with Shanghai Synchrotron Radiation Facility, University College London, and Research Complex at Harwell, designed and manufactured 2024 aluminium matrix composites containing different TiB2 particles by laser powder bed fusion (LPBF) technology. The as-printed xTiB2/2024Al composites show weak texture and duplex microstructure with refined grains. A quantitative relationship between TiB2 particle content and grain size is proposed, which can be utilized to predict and control the grain size of TiB2 particle reinforced composites under the LPBF process. The research results were published in the Materials Research Letters (IF=8.516) under the title of “The role of in-situ nano-TiB2 particles in improving the printability of non-castable 2024Al alloy”.
https://doi.org/10.1080/21663831.2022.2080514
In addition to the design of special material system, it is also critical to explore the process conditions suitable for forming. Keyhole-induced porosities under high energy density can potentially affect the mechanical properties of the fabricated parts. Based on the dynamic characteristics of the melt pool and the keyhole observed by in-situ X-ray imaging technology, the group established a multiphysics model to reveal the different keyhole-pore formation mechanisms. The effects of the powder on the characteristics of the keyhole, molten pool, and pore formation were explored. In addition, a relationship map between the input energy density and pore number was built via a high-throughput simulation, providing a strategy to reduce or remove the pores in LPBF.The research results were published in the International Journal of Machine Tools and Manufacture (IF=10.331) under the title of “Understanding keyhole induced-porosities in laser powder bed fusion of aluminium and elimination strategy”.
https://doi.org/10.1016/j.ijmachtools.2022.103977
Non-ferrous materials such as aluminium and copper have high reflectance to a traditional infrared laser. Therefore, industry and academia have a high hope for the 450 nm blue laser, which has a high absorptivity for high reflectivity materials. The group took the lead in building a 2000 W blue laser AM prototype system. Combined with the multi-source sensor monitoring method, they established the method of characterizing the molten pool metallurgical dynamics state by the internal area characteristics of the molten pool, constructed the mapping relationship between process parameter, sensing signal, molten pool characteristic, metallurgical features and key quality. At last, blue laser-based directed energy deposition of thin-wall aluminium alloy blade was successfully achieved. The research results were published in the Virtual and Physical Prototyping (IF=10.962) under the title of “2000W blue laser directed energy deposition of AlSi7Mg: process parameters, molten pool characteristics, and appearance defects”.
https://doi.org/10.1080/17452759.2022.2120405
The surface quality of metallic components fabricated by laser AM is mainly determined by spheroidization, ripple, and step effects. Considering the effect of forming process parameters on further improving surface quality is limited, there is an urgent need to develop more efficient electrochemical post-treatment methods. Based on different regions of the electrochemical polishing curve, the group reviewed the research progress of electrochemical methods in the surface treatment of metallic AMed parts from the aspects of the latest electrochemical methods and theories, factors, application analysis, comparison with traditional post-treatment methods, and composite electrochemical polishing methods. This review was published in the journal Progress in Materials Science (IF=48.165) under the title of “Application of electrochemical polishing in surface treatment of additively manufactured structures: A review”.
https://doi.org/10.1016/j.pmatsci.2023.101109
AM provides unprecedented design freedom for complex structural design. In the past decade, mechanical metamaterials with highly complex artificially designed internal structures that achieve exotic mechanical properties not found in natural materials have gained widespread attention in the fields of materials science and AM. Collaborating with Professor Chu Lun Alex Leung from University College London and Professor Yaoyao Fiona Zhao from McGill University in Canada, the group investigated the mechanical properties of honeycomb multilevel structures and proposed a bio-inspired multilevel spherical lattice metamaterial with ultra-high specific energy absorption. Experimental results have shown that the developed metamaterials exhibit significantly improved energy absorption performance compared to existing materials of the same density. By using a data-driven approach, they also proposed a bio-inspired composite metamaterial with a complex fiber helix structure that exhibits both ultra-high specific energy absorption and high recovery capacity similar to rubber. The research results were published in Composites Part B: Engineering (IF=11.322) under the titles of “Additively manufactured high-energy-absorption metamaterials with the artificially engineered distribution of bio-inspired hierarchical microstructures” and “Data-driven design of biometric composite metamaterials with extremely recoverable and ultrahigh specific energy absorption”.
https://doi.org/10.1016/j.compositesb.2022.110468
https://doi.org/10.1016/j.compositesb.2022.110345