Tungsten is the material of choice for high-temperature applications due to its good thermomechanical properties such as high melting point, high density, high thermal conductivity， and moderate thermal expansion. In addition, its high density and extremely low sputtering erosion rate make it suitable for radiation or other extreme environments and can be used to manufacture waveguides, collimators, nuclear reactor plasma surface components, etc., covering aerospace, aviation, military, medical and nuclear industries, etc. Many fields.
The wide range of advantages of tungsten metal also makes it difficult to process. The melting point of pure tungsten is as high as 3410 degrees Celsius. Although the melting point of tungsten alloy is lowered, they are all refractory metals, which are difficult to manufacture by conventional methods. Generally, tungsten and tungsten alloys can be processed into materials by powder metallurgy blank making, extrusion, forging, rolling, spinning, and drawing, but the processing cost is high and time-consuming, and the structural complexity of the parts that can be manufactured is limited.
In recent years, 3D printing technology has provided a means for the manufacture of tungsten metal, and the manufacture of this material has been explored using different 3D printing processes such as SLM, BJ, FDM extrusion, and DLP, which are based on direct melting and sintering. feasibility. Cemented carbide manufacturing companies hope that this new technology can open up a new way for the manufacture of tungsten metal, and mainstream 3D printing equipment manufacturers have also actively explored the forming process of tungsten metal and expressed that they have made breakthroughs.
Melting-based, direct laser 3D printing
Selective laser melting (SLM/L-PBF) is one of the most successful additive manufacturing techniques for producing high-precision and high-quality functional parts. Over the years, well-known metal 3D printing manufacturers in China have stated that they have conquered the laser 3D printing of tungsten and successfully realized the application. The examples given are all tungsten grids for medical use, and there are few sustainable ones. reports.
The biggest problem with laser-based technology is the existence of temperature gradients, which can easily lead to residual stress and cause cracking. Researchers at Lawrence Livermore National Laboratory pointed out that in 3D printing studies on tungsten, high densities greater than 98% have been reported, but the formation of microcracks is unavoidable. 3D printing technology reference has learned about researchers from several units engaged in the research of this material. Tungsten grids are relatively easy to print. Although the strength is not high, they can meet the medical requirements for radiation shielding. Very easy to crack during printing.
Laser printing of tungsten can be improved through alloying and process optimization, but both approaches have had limited success. For high-density tungsten alloys, due to the variety of components, the properties vary greatly, the melting point varies up to 2400°C, and the saturated vapor pressure of each element is different. Researchers from Tianjin University and Central South University also pointed out that it is difficult to ensure the controllability of the components in tungsten alloys by using SLM, and it is also difficult to manufacture full-density tungsten alloys with excellent mechanical properties.
Undoubtedly, the use of the laser to manufacture tungsten grids is a significant breakthrough and the most successful application of direct laser melting, but the application of tungsten is not just for grids.
Sintering-based, indirect 3D printing
Indirect 3D printing based on sintering provides another processing method for forming tungsten metal materials. The main processes include extrusion, light curing, and binder jetting. These processes are to form the blank of the part first, and then use the traditional powder metallurgy process to realize the sintering and densification of tungsten metal.
Powder Extrusion printing (Powder Extrusion printing, PEP) is an example, this technology does not have strict requirements on the sphericity and fluidity of the original powder, by heating the pellets mixed with metal powder and polymer binder into a molten paste Fluid, and depositing it layer by layer to produce a green body, after degreasing and sintering, an alloy part with the desired structure and high performance can be formed.
Tungsten alloy green body
Tungsten alloy after sintering
The use of powder melt extrusion indirect 3D printing technology has certain advantages in printing tungsten alloy parts, making it possible to manufacture near-net-shape structural parts. Moreover, this forming process is simple, does not require laser devices, and has low equipment and material input costs. It is suitable for powder materials used in powder metallurgy and has the characteristics of low-temperature forming and high-temperature forming.
Summarize
Each process has its own advantages and disadvantages. The current direct laser manufacturing of tungsten metal blocks has deficiencies in cracking and forming, and the scheme of extrusion and sintering is difficult to manufacture thin-walled grid structures.