Tungsten powder metal tungsten is the raw material for preparing tungsten processed materials, tungsten alloys, and tungsten products. It is grayish-black metal with metallic luster (body-centered cubic crystal). Melting point 3400℃. Boiling point 5555℃. The hardness of tungsten is the hardest among metals. The hardness of sintered tungsten bars is 200-250, and that of tungsten rods after the rotary hammer is 350-400.
Mixed acid dissolved in nitric acid and hydrofluoric acid. Melt with a mixture of sodium hydroxide and sodium carbonate. Slightly soluble in nitric acid, sulfuric acid, aqua regia, insoluble in water, hydrofluoric acid, potassium hydroxide. There are two variants of tungsten, a and B. At standard temperature and normal pressure, type a is a stable body-centered cubic structure. B-type tungsten can only appear in the presence of oxygen. It is stable below 630 ℃, converted to tungsten above 630 ℃, and is irreversible.
In addition to specific requirements for the impurity content of tungsten powder, the oxygen content should be controlled within a particular range. The particle size of commonly used tungsten powder is generally Fischer's average particle size, two～10μm. The tungsten powder is in the shape of polygonal particles. Besides, the specific surface, bulk density, and tap density of tungsten powder also vary within a particular range. The performance of tungsten powder has a direct impact on the production of tungsten materials. The quality of tungsten powder metallurgy products, especially the effect of purity and particle size, is more prominent. Tungsten powder is classified according to virtue and particle size and different uses.
Most of the tungsten is used to produce cemented carbide and Ferro tungsten. Tungsten, chromium, molybdenum, and cobalt are heat-resistant and wear-resistant alloys used to make tools, hardened materials for metal surface, gas turbine blades, and combustion tubes. Tungsten and tantalum, niobium, molybdenum, and other refractory alloys. Tungsten copper and tungsten silver alloys are used as electrical contact materials. High-density tungsten-nickel-copper alloy is used as a shield against radiation.
Metal tungsten wires, rods, sheets, etc. are used to make light bulbs, electron tubes, and electrodes for arc welding. Tungsten powder can be sintered into various porosity filters. FW-1 is used as raw material for large slab and tungsten rhenium couplers. FW-2 is used for contact alloy and high specific gravity shielding raw materials. FWP-1 is used for plasma spraying materials.
Tungsten powder is the primary raw material for processing powder metallurgy tungsten products and tungsten alloys. Pure tungsten powder can be made into processed materials such as wires, rods, tubes, plates, etc. and certain shaped products. Tungsten powder is mixed with other metal powders to make various tungsten alloys, such as tungsten-molybdenum alloy, tungsten-rhenium tungsten-copper alloy and high-density tungsten alloy. Another critical application of tungsten powder is to make tungsten carbide powder and then to prepare cemented carbide tools, such as turning tools, milling cutters, drill bits, and molds.
Tungsten is a compact and robust metal. Its excellent corrosion resistance has been widely used in many fields, such as the chemical industry. However, its high hardness and high melting point have hindered its development in 3D printing. Now, a research team has challenged this problem and published a paper entitled "The Influence of Processing Parameters in the Laser Powder Bed Fusion Process on the Densification, Microstructure and Crystal Structure of Pure Tungsten."
The researchers explained: "We applied the laser powder bed manufacturing process to refractory metals, such as the pure tungsten powder in the paper. A process scheme for manufacturing high-density parts was proposed, and the effect of laser energy density was studied. Researchers evaluated the process quality using techniques such as optical microscopy, XCT, SEM, and EBSD. The results show that the laser energy density can process tungsten materials into good functional parts."
Depending on the process conditions, the volume density of tungsten and the optically measured density range from 94% to 98%, but due to the presence of micro and macro residual stresses, the parts still show defects such as micro cracks.
The researchers continue to introduce: "The analysis results of the microstructure and crystal structure show that the melting groove formed under the laser beam is cured by the epitaxial growth mechanism to achieve the ideal orientation. The texture analysis results of EBSD show that tungsten has //Z Is parallel to the direction of construction."
Both types of tungsten samples were produced by 3D printing and analyzed using a scanning electron microscope. Although these parts still have the problem of natural cracking, the researchers determined that as long as the density and quality of 3D printed samples are improved, they will make a lot of difference in the fields of medical radiation protection and nuclear imaging, and other plasma environments in the future. They also concluded that laser powder bed fusion technology could be used to manufacture relatively dense tungsten parts.
The researchers also added: "The results of micro, macro, and local texture analysis show the columnar grain structure produced by the epitaxial growth mechanism, which is consistent with the performance of other pure metals. Laser energy with a density of up to 348 J/mm3 can The sample shows a strong //Z fiber structure. It is speculated that this may be related to the shape of the melting tank, the high thermal conductivity of tungsten, the low surface tension, and the 67° grating direction rotation of the deposited layer in Renishaw AM. Caused this phenomenon."
3D printing can provide new application opportunities for tungsten materials, producing parts with high precision and complexity. Other researchers have studied the 3D printing process of tungsten materials, some of which have even been commercialized. Despite the challenges, tungsten has proven to be a valuable 3D printing material, and many experts are interested in its heat resistance.
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