in refractory metals

In the 1950s, China has been able to produce tungsten material. 1960 tungsten smelting, metallurgy and processing carried out research, is now able to produce plate, sheet, foil, bar, pipe, wire and other shaped pieces. Tungsten materials using high temperature, only using the solid solution strengthening methods to improve the high temperature strength of tungsten little effect. However, in the solution based on the further strengthening dispersion (or precipitation) hardening, to greatly improve the high temperature strength, and precipitated with ThO2 HfC particle dispersion strengthening effect is best. At 1900 ℃ or so W-Hf-C system and the W-ThO2 alloys have a high-temperature strength and creep strength. Used below the recrystallization temperature of the tungsten alloy, taking temperature hardening methods, to produce strain hardening is an effective way to strengthen. Such as fine tungsten wire wire with high tensile strength, deformation rate of 99.999% total processing a diameter of 0.015 mm thin tungsten wire, room temperature tensile strength of up to 438 kg / mm; in refractory metals, tungsten and tungsten alloy plastic - brittle transition temperature maximum. Sintering and melting of the plastic material of polycrystalline tungsten - brittle transition temperature is about 150 ~ 450 ℃ between, resulting in difficulties in processing and use, and the single crystal of tungsten is below room temperature. Tungsten material in the interstitial impurities, microstructure and alloy elements, and plastic processing and surface state, the plastic timber tungsten - brittle transition temperature has a significant impact. In addition to tungsten rhenium can significantly reduce the plastic timber - brittle transition temperature, the other alloying elements on the lower plasticity - brittle transition temperature have little effect (see the metal reinforcement). Poor oxidation resistance of tungsten oxide, molybdenum similar characteristics and, above 1000 ℃ volatile tungsten trioxide will occur, resulting in "catastrophic" oxidation. Therefore, high temperature tungsten materials must be used in a vacuum or inert atmosphere protection, if used in high temperature oxidizing atmosphere, you must add a protective coating.According to different purposes, tungsten carbide alloys are divided into high proportion alloy, metal sweating materials, contact materials, electronics, and electric light materials.