Harbin University Of Technology Made A New Breakthrough in Diamond 3D Printing Technology

Core abstract: Recently, Professor Zhu Jiaqi of Harbin University of Technology proposed a method to adjust the accuracy saturation of the embryo in the production of binder spray additive based on the rapid in-situ curing process.

Source: Materials Science and Engineering

Recently, Professor Zhu Jiaqi of Harbin University of Technology proposed a method to adjust the accuracy saturation of the embryo in the process of binder spray additive manufacturing based on the rapid in-situ curing process. According to this method, the formation of high precision/saturation embryo can be realized, and the internal relationship between the strength of binder itself and the strength of embryo can be strengthened to the greatest extent, which is of great significance to the basic research on the formation quality in the field of adhesive additive manufacturing.

Relevant achievements were published on Additive Manufacturing, an international top journal of additive manufacturing, under the title of Overcoming the penetration – saving trade off in binder jet additive manufacturing via rapid in situ cutting.

Paper link: https://doi.org/10.1016/j.addma.2022.103157

Research background

Diamond/metal matrix composites are regarded as the next generation of thermal management materials because of their high thermal conductivity and low thermal expansion, and have great application prospects. However, due to the high hardness of diamond, there is no good post-treatment method such as polishing and polishing at present, so the near net forming process of diamond/metal matrix composites is the focus of current research. Among them, the 3D printing technology of diamond/metal matrix composites has attracted extensive attention.

Binder Jetting (BJ) is a 3D printing technology applicable to various materials. During the processing, the binder is directionally deposited on the powder bed to produce embryo with complex three-dimensional structure. The interaction between binder and powder is affected by the physical properties of the relevant solid-liquid system and the pore structure of the powder bed, which makes it difficult to accurately describe the entire printing process with a simple physical model. Due to the PSTO, there is an inevitable contradiction between the size accuracy and strength of embryos produced by BJ. The strength of embryo body increases with the increase of effective saturation, but the increase of penetration distance has adverse effects on its size accuracy. In order to overcome PSTO, researchers often focus on the optimization of processing parameters (such as powder particle size, layer thickness or drying conditions). Although researchers have made great efforts in this area, the problem of PSTO has not been solved well.

Fig. 1 Schematic diagram of binder injection principle

research contents 

In this study, in order to overcome PSTO, the research team developed a rapid in-situ curing (rapid curing of adhesives during printing) adhesive spray additive manufacturing technology based on the self-developed acrylic adhesive. The use of pure copper powder as printing material has laid a foundation for the research on additive manufacturing of diamond/copper composites.

Fig. 2 Performance characterization of fast curing acrylic adhesive

(a) TGA and DSC curves of binder, (b) DSC curve of binder, (c) FTIR of binder without TBPB heated at different temperatures, (d) FTIR of 2wt% TBPB binder heated at different temperatures

Figure 3 shows the relationship between penetration distance and ink-jet times. In the samples that are not cured in situ (the adhesive is not cured during the printing process), the penetration distance mainly depends on the amount of single inkjet, which increases slightly with the increase of the amount of inkjet. On the contrary, in the in situ solidified samples, the penetration distance increased significantly with the increase of the amount of inkjet.

Fig. 3 Relationship between Permeation Distance, Saturation and Injection Times

(a) Non in-situ curing, (b) in-situ curing

Under the semi in situ curing condition (the traditional process of curing the adhesive with infrared lamp), the penetration distance is mainly related to the total amount of single layer adhesive, and the penetration distance increases with the increase of the amount of adhesive sprayed. Since the saturation related to each layer is overlapped in the multi-layer printed sample, the saturation of the multi-layer printed sample exceeds that of the single-layer printed sample. Compared with non in-situ curing printing method, semi in-situ curing with the same saturation has a lower penetration distance, which shows that semi in-situ curing can reduce the penetration distance to a certain extent and overcome PSTO. Based on the above analysis, the penetration models of adhesives under different processes were established.

Fig. 4 Establishment of infiltration process model under different processes

(a) Non in-situ curing, (b) semi in-situ curing, (c) in-situ curing

The relationship between infiltration distance and saturation is shown in Figure 5. Under the non in-situ curing condition, the penetration distance mainly depends on the amount of single binder injection, and the saturation increases with the number of binder injections; At a specific saturation, the penetration distance of the in-situ solidified print sample is the lowest, which overcomes the PSTO brought by the traditional BJ.

Fig. 5 Relationship between Permeability Distance and Saturation

Summary and outlook

In this study, the research team developed a methacrylate adhesive system with thermal initiation and rapid curing, which proved that the in-situ curing conditions can improve the accuracy and strength of printing embryos. Single layer and multi-layer printing experiments were carried out to determine the printing characteristics of the binder powder system under different printing and curing conditions, providing a basis for deriving the physical models of printing in situ, semi in-situ and in-situ conditions. In addition, the relationship between saturation and penetration distance related to different curing conditions was discussed. This study provides a reference for the further development of in-situ curing (UV or heat activated) adhesives and printing technology.

Transformation and application

Taking diamond/copper composites as an example, copper and its alloys have excellent thermal conductivity (350W/m · K) and excellent bending bearing capacity, and are widely used in high-performance thermal management materials. Diamond is the material with the highest thermal conductivity in nature, and its thermal conductivity can reach 2000W/m · K. Therefore, the structure/thermal conductivity integrated material with diamond/copper composite as the system has excellent mechanical properties, but also has a high thermal conductivity of more than 700 W/m · K and less than 10 × The low thermal expansion coefficient of 10-6 is the most potential material to solve the heat dissipation problem of electronic devices. In the future, the use of diamond/copper composites is not limited to the basic shapes such as round hexagon, and the demand for heterogeneous diamond/metal alloy composites is increasing. However, the diamond material is very hard, and the processing cost accounts for more than 65% of the total cost of the material, which makes the traditional hot pressing sintering and other methods ineffective. This technology provides a good idea for the high-precision additive manufacturing of diamond/copper and other diamond/metal matrix composites, and injects new vitality into the additive manufacturing research of diamond/copper materials. It has great application potential in radar, new energy vehicles, power devices, 3C electronics and other structural heat dissipation integrated high heat flux fields.

The laboratory independently developed a series of diamond/metal matrix composites, including but not limited to diamond/copper, diamond/titanium, diamond/tungsten, diamond/nickel, etc., and developed corresponding batch preparation processes. Based on the microstructure of micro scale materials, a heat transfer model is established. Combined with the simulation of carbide crystal growth process and the calculation of interface thermal resistance crystal structure model, the development and optimization of the calculation principle of composite interface heat transfer are completed. The original controllable diamond metallization process provides a guarantee for the multi-scale optimization of thermal conductivity of diamond/metal matrix composites.

Fig. 6 Diamond/copper powder products independently developed by the laboratory

Based on the research and development of diamond/metal matrix powder materials and the optimization of additive manufacturing process, the laboratory developed a diamond/metal composite material represented by aluminum and copper, which is suitable for the molding of heterogeneous parts. The thermal conductivity is up to 700W/m · K, and the thermal expansion coefficient is ≤ 10 × 10-6, with a strength of 220MPa, has huge application potential in the field of thermal management. Through multi-scale thermal conductivity structure optimization, the thermal management efficiency of diamond/copper composites is improved, the bottleneck of low overall thermal conductivity of composites is broken, and the design and manufacturing of complex and efficient thermal management structures are realized, which greatly expands the application prospects of diamond/metal matrix composites and improves their engineering potential.

Fig. 7 Additive manufacturing products

(a) Diamond copper printing series products, (b) diamond/aluminum printing series products, (c) ceramic material printing series products