The invention relates to a molybdenum base alloy and a preparation method thereof
The test data of pure molybdenum show that the strength of pure molybdenum is about δB = 40kg/mm2 at 20℃, 7kg/mm2 at 1000℃, and only 1.2kg/mm2 at 2000℃. Therefore, pure molybdenum has no unique physical properties such as high temperature strength and oxidation resistance. However, molybdenum is a metal that can maintain the high-temperature strength and corrosion resistance of its alloy, that is, molybdenum in the form of alloy can have unique physical properties, for example, molybdenum alloy components such as mandrel head and crucible used in steel tube rolling mill can work in harsh environment.
In the existing technology, many kinds of technologies about the composition and preparation of molybdenum alloys have been put forward. For example, Chinese patent 1540017 "a method for preparing low oxygen TZM molybdenum alloy rod billet" is an example. In this method, high carbon molybdenum powder, titanium hydride and zirconium hydride are used as raw materials to make molybdenum alloy rod billet by mixing and sintering. Its meaning is to use carbon as deoxidizer, and generate carbon monoxide gas, at the same time, using trace zirconium element to improve the high temperature strength of molybdenum and trace titanium to improve the recrystallization temperature of molybdenum. Although this kind of molybdenum and molybdenum alloy as-cast alloy compared with low cost, simple process and relative higher life advantages, but, the preparation of the alloy in ingredients must control the content of carbon, because of excessive amounts of carbon and molybdenum compound generated after molybdenum carbide can make the plasticity and toughness of molybdenum alloy is reduced, enhanced and brittle, and appear crack and other issues; In addition, the hydrogen released from titanium and zirconium hydride during carbonization reacts with the remaining oxygen to generate more water, which will hinder the movement of grain boundaries and form holes in the removal process, thus affecting the service life of molybdenum alloys.
In addition, Chinese patent No. 1083900 also discloses a technology named "a preparation method of a doped molybdenum alloy". In this method, the doped ammonium paramolybdate is prepared by mixing the solution of ammonium paramolybdate with the solution of rare earth salt, and then the doped molybdenum powder is reduced to ammonium paramolybdate, and processed into various products through molding and sintering process. Obviously, liquid-liquid doping method is used to prepare molybdenum alloy powder, so that rare earth elements can be evenly distributed in molybdenum to form composite oxides, so as to effectively improve the comprehensive mechanical properties of molybdenum material. However, there are some differences between this method and the powder metallurgy method for preparing molybdenum base alloy.
In particular, the active component added to the molybdenum base alloy only accounts for about 3% of its total weight, and its particle size is an important parameter to evenly and fully mix the active component with the molybdenum powder, which determines the impurity concentration and other properties on the unit grain boundary of the molybdenum base alloy. If the particle size of the active component is too large, the concentration of impurities on the unit grain boundary will increase, and the impurities contain atomic oxygen and carbon and other elements on the grain boundary segregation, the trend of intergranular fracture will increase, resulting in the strength and other properties of the alloy reduced. At the same time, the large particle size can also affect the intermolecular diffusion, so that the alloy can not be fully alloyed in the sintering process, and there are large pores in the alloy matrix, and then prone to crack, seriously affect the service life of the alloy.
