Molybdenum tungsten alloy
It includes molybdenum tungsten alloy based on molybdenum and tungsten molybdenum alloy series based on tungsten. The alloy can be formed in any proportion and is a complete solid solution alloy at all temperatures.
Properties (1) the melting point of molybdenum tungsten alloy increases with the increase of tungsten content. When the tungsten content increases to 25%, the melting point of the alloy is about 200 ℃ higher than that of pure molybdenum. Therefore, according to the service temperature and the required melting point of the alloy, the corresponding alloy composition can be selected in the range of 2620 ~ 3410 ℃. This advantage is also one of the advantages that molybdenum tungsten alloy can be widely used. The relationship between tungsten content and melting point of molybdenum tungsten alloy is shown in the figure. (2) The lattice constant and density of Mo-W alloy increase linearly with the increase of W content. The hardness and strength of Mo-W alloy increase with the increase of W content. (3) The highest room temperature hardness value of the alloy is between 90% and 100% of tungsten content, and its Vickers hardness value is as high as 3530 ~ 3860mpa, which is more than twice as high as that of pure molybdenum. The highest high temperature hardness of the alloy is between 70% and 85% of tungsten content. When the W content increases from 0% to 40%, the room temperature tensile strength of Mo-W alloy increases from 617 MPa to 900 MPa. The hardness values of molybdenum tungsten alloy ingots by vacuum arc melting are listed in the table.
Strengthening mechanism the strengthening effect of binary Mo-W alloy is mainly solution strengthening and strain strengthening. When titanium, zirconium, niobium, carbon and other alloying elements are added into the alloy, the precipitation strengthening effect is obvious. The nominal compositions of commonly used molybdenum tungsten alloys are mo-20w, mo-30w, mo-50w, mo-75w, mo-90w and mo-25w-0.1zr-0.03c, mo-25w-1.67nb-1.37ti-0.12zr-0.18c.
There are three production methods of molybdenum tungsten alloy ingots: powder metallurgy, vacuum arc melting and vacuum electron bombardment melting. Powder metallurgy is the most widely used method because it is simple and can obtain alloy ingots with fine grains, which is conducive to plastic processing. The main process of powder metallurgy is: mechanical mixing molybdenum powder and tungsten powder in proportion; pressing the raw blank by mechanical press or isostatic press; sintering alloy ingot in high temperature sintering furnace with hydrogen. The sintering temperature increases with the increase of tungsten content, which ranges from 2150 ℃ to 2300 ℃. Finally, the sintered billets are rolled or forged into products.
Application molybdenum tungsten alloy can be used at higher temperature than molybdenum or molybdenum alloy. For example, when molybdenum tungsten alloy is used as electrode, flow mouth and thimble components in the wave batch furnace for producing high melting point refractory ceramic fiber, its service life is much longer than that of pure metal molybdenum products. Mo-30w has higher corrosion resistance than pure molybdenum in molten zinc. It is widely used in zinc temperature measuring tube, zinc pump rotor and some corrosion-resistant parts of zinc smelting furnace. Because of its high melting point, good ablation resistance and flame erosion resistance of solid particles, Mo-W alloy can also be used in gas rudder and guard plate of solid rocket motor. The nominal compositions of commonly used molybdenum tungsten alloys are mo-30w, mo-50w and mo-85w. Molybdenum tungsten alloy can be regarded as the transition alloy between molybdenum and tungsten. Therefore, the alloy can be used in a wide temperature range between molybdenum and tungsten.
