Tungsten Alloy (High Specific Gravity Tungsten Alloy)

Tungsten alloy is an alloy composed of tungsten as the base and other elements. Among metals, tungsten has the highest melting point, high temperature strength and creep resistance, as well as thermal conductivity, electrical conductivity and electron emission properties. It is used in the electronics and electric light source industries, and also in the aerospace, casting, weapons and other departments to make rocket nozzles, die-casting molds, armor-piercing cores, contacts, heating elements and heat shields.

According to different uses, tungsten alloy is divided into cemented carbide, high specific gravity alloy, metal sweating material, contact material, electronic and electric light source material.

Molybdenum-tungsten alloy is an alloy containing two elements, molybdenum and tungsten. It includes molybdenum-based molybdenum-tungsten alloy and tungsten-based tungsten-molybdenum alloy series. This alloy can be formed in any proportion and is a complete solid solution alloy at all temperatures.

Niobium-tungsten alloy is a niobium alloy formed by adding a certain amount of tungsten and other elements based on niobium. Tungsten and niobium form an infinite solid solution. Tungsten is an effective strengthening element of niobium, but with the increase of tungsten addition, the ductility-brittle transition temperature of the alloy will rise, and the grains will grow significantly. Therefore, in order to obtain a high-strength niobium-tungsten alloy, the amount of tungsten added must be properly controlled, and an appropriate amount of elements such as zirconium and hafnium that can refine grains and reduce the ductility-brittle transition temperature must be added. In 1961, the United States successfully developed Nb-10W-2.5Zr alloy for the skin of the space shuttle, and later developed into Nb-10W-1Zr-0.1C alloy. In the early 1970s, China also successfully developed NbWl0Zr2.5 and NbWl0Zr1C0.1 alloys.

Tungsten alloy (high specific gravity tungsten alloy) is usually a refractory metal, generally composed of W-Ni-Fe (tungsten-nickel-iron) or W-Ni-Cu (tungsten-nickel-copper) or W-Ni-Cu-Fe (tungsten-nickel-copper) -Nickel-copper-iron), some tungsten alloys also add Co (cobalt), Mo (molybdenum), Cr (chromium), etc. They have high melting points, are twice as dense as steel, and are 50% heavier than lead. The content of tungsten in the alloy usually accounts for 90%~98%, which is why the tungsten alloy can have a high density (usually 16.5g/cm3~18.75g/cm3). Ni, Fe, and Cu are used as binders to bond the brittle tungsten together, thereby enhancing the ductility of the tungsten alloy and making it easy to process. Ni-Fe is a commonly used additive, and its ratio is 7Ni:3Fe or 8Ni:2Fe (weight ratio).

The conventional production process of tungsten alloy (high specific gravity tungsten alloy) includes compounding, cold pressing and liquid phase sintering until the desired density. In the process of liquid phase sintering, the base alloy is in a molten state, which helps the tungsten to dissolve in the liquid better, so that the large tungsten particles (20-60 microns) are dispersed in the base alloy. The sintered material is usually subjected to a thermomechanical treatment process, such as forging, in order to increase its hardness and strength. At present, the composition of high specific gravity tungsten alloys is WNiFe, such as 93W-4.9Ni-2.lFe and 95W-4Ni-lFe. Adding appropriate amount of cobalt to WNiFe alloy can enhance its strength and ductility.