Application of tungsten alloy as high temperature material
It is not effective to improve the high temperature strength of tungsten simply by solid solution strengthening. However, on the basis of solid solution strengthening, dispersion (or precipitation) strengthening can greatly improve the high temperature strength, ThO2 and precipitation of HfC dispersion particles have the best strengthening effect. Both the w-hf-c and w-tho2 alloys have high high-temperature strength and creep strength at about 1900℃.It is an effective way to strengthen tungsten alloys used below the recrystallization temperature by means of warm working and hardening. For example, fine tungsten wire has a high tensile strength, the total processing deformation rate of 99.999%, the diameter of 0.015 mm of fine tungsten wire, the tensile strength at room temperature up to 438 kg force/mm.
Among refractory metals, tungsten and tungsten alloys have the highest ductile-brittle transition temperatures. The plastic-brittle transition temperature of sintered and fused polycrystalline tungsten is about 150 ~ 450℃, which makes it difficult to process and use, while the single-crystal tungsten is lower than room temperature. The interstice impurities, microstructure and alloying elements in tungsten as well as the plastic processing and surface state have a great influence on the ductile-brittle transition temperature of tungsten. Except rhenium, which can obviously reduce the ductile-brittle transition temperature of tungsten, other alloying elements have little effect on reducing the ductile-brittle transition temperature (see strengthening of metals).
Tungsten has poor antioxidant properties and similar oxidation characteristics with molybdenum. Tungsten trioxide volatilizes at more than 1000℃, resulting in "disastrous" oxidation. Therefore, tungsten material high temperature use must be in the vacuum or inert atmosphere protection, if the use of high temperature oxidation atmosphere, must add protective coating.
