High temperature molybdenum/molybdenum lanthanum alloy MoLa alloy processing and customization
Molybdenum lanthanum alloy is composed of matrix metal molybdenum and lanthanum trioxide in the matrix as a dispersed particle. The La2O3 content in the alloy is generally 0.5%~5.0%(mass fraction).
Molybdenum is an important high temperature structural material with high melting point, excellent high temperature performance, good electrical and thermal conductivity. However, due to the high brittleness transition temperature of molybdenum, molybdenum used at high temperature (higher than recrystallization temperature) will show serious brittleness when returned to room temperature. Therefore, researchers at home and abroad have done a lot of research on the addition of rare earth to molybdenum, and it is concluded that adding rare earth to molybdenum can refine grain, reduce the brittle-forming transition temperature of molybdenum, improve the recrystallization temperature, high temperature strength, improve the toughness and plasticity and high temperature creep properties of molybdenum.
It is found that the addition of lanthanum oxide can greatly improve the mechanical properties of molybdenum, and the lanthanum molybdenum after high temperature heat treatment has excellent strength and toughness at room temperature or liquid nitrogen temperature region. However, the study of lanthanum oxide behavior in plastic deformation and heat treatment is not enough. In recent years, a large number of tests have been carried out on lanthanum molybdenum alloy in the West Refractory Material Factory, and the powder, pressing, sintering, sheet rolling and sheet properties have been systematically studied.
The lanthanum molybdenum alloy was doped in molybdenum powder in the form of La(NO3)3 alcohol solution by liquid-solid mixing method. The amount of lanthanum oxide was about 1%. The molybdenum powder was pretreated at 700~900℃ for 2 h in hydrogen atmosphere, and after isostatic pressing, the lanthanum molybdenum alloy billet with relative theoretical density of 92%~96% was formed by high temperature firing.
After the blank of lanthanum molybdenum alloy was opened at 1500℃, the sheet was rolled to 2.4 mm thick through warm rolling and cold rolling. The processing rate of each pass is 25%~35%, and the total processing rate is 80%. The rolled lanthanum molybdenum plate was annealed in hydrogen furnace at 1100, 1250, 1400, 1550 and 1950℃, respectively.
The rare earth element lanthanum does not react with molybdenum and exists in molybdenum matrix in the form of lanthanum La2O3. In alloy powder, rare earth lanthanum is embedded on the surface of molybdenum powder in the form of La2O3. In the sintered billet, La2O3 particles are evenly distributed, not only in the molybdenum grain boundary, but also in the molybdenum grain. The size of rare earth particles on the grain boundary is generally larger than that in the grain. Rare earth oxide particles mainly exist in spherical and equiaxed form.
The La2O3 particles of lanthanum molybdenum alloy plate are very small and difficult to identify when it is heat treated below 1400℃. Heat treatment above 1400℃, La2O3 small particles gathered into larger spherical or short rod like small particle string, and after 1550℃, with the increase of heat treatment temperature, La2O3 particle size and shape change little.
Molybdenum element is located in the VIB group in the periodic table. It is a high melting point and high strength metal with high elastic modulus, small expansion coefficient and excellent electrical and thermal conductivity. It is an ideal matrix material for superalloys. The rare earth molybdenum plate made by powder metallurgy and pressure processing with appropriate rare earth elements added into molybdenum powder has good mechanical and technological properties at high temperature. It is widely used in high-temperature furnace, electronic components, heating element and iron and steel smelting industry as a vessel, heat insulation screen and high temperature structure.