Molybdenum lanthanum alloy is an alloy composed of molybdenum and lanthanum trioxide in the matrix. The content of La2O3 in the alloy is generally 0.5% ~ 5.0% (mass fraction).
History of molybdenum lanthanum alloys
Molybdenum is an important high temperature structural material with high melting point, excellent high temperature performance, good conductivity and heat conduction. However, due to the higher plastic brittle transition temperature of molybdenum, molybdenum used at high temperature (higher than recrystallization temperature) will appear serious brittleness when it returns to room temperature. Therefore, researchers at home and abroad have carried out a lot of research on the addition of rare earth in molybdenum. It is concluded that adding rare earth in molybdenum can refine grain size, reduce the plastic brittle transition temperature of molybdenum, increase the recrystallization temperature, high temperature strength, improve the toughness plasticity and high temperature creep properties of molybdenum.
It is found that the mechanical properties of molybdenum are greatly improved by adding a small amount of lanthanum oxide. After high temperature heat treatment, the lanthanum molybdenum material has excellent strength and toughness at room temperature (liquid nitrogen temperature). However, the behavior of lanthanum oxide in plastic deformation and heat treatment is not fully studied. In recent years, a large number of tests have been carried out on molybdenum lanthanum alloy in the refractory plant of Western materials. The powder, pressing, sintering, rolling of thin plate and properties of the plate are systematically studied.
Preparation of molybdenum lanthanum alloy blank
In this paper, La (NO3) 3 was doped into molybdenum powder by liquid-solid mixing method. The molybdenum powder was pretreated at 700 ~ 900 ℃ for 2 h in hydrogen atmosphere. After static pressing, the molybdenum powder was sintered at high temperature to form molybdenum lanthanum alloy blank with relative theoretical density of 92% ~ 96%.
Rolling and heat treatment of Mo La alloy sheet
The molybdenum lanthanum alloy blank is rolled and cold rolled to 2.4 mm thick plate after being opened at 1500 ℃. The pass processing rate is 25% ~ 35%, and the total processing rate is 80%. The rolled Mo La plates were annealed in hydrogen furnaces at 1100, 1250, 1400, 1550 and 1950 ℃ respectively.
Research conclusion of Mo La alloy plate
Lanthanum does not react with molybdenum and exists in molybdenum matrix in the form of lanthanum La2O3. In the alloy powder, lanthanum is embedded on the surface of molybdenum powder in the form of La2O3. La2O3 particles are distributed uniformly in the sintered billets, not only on the molybdenum grain boundaries, but also in the molybdenum grains. The grain sizes of rare earth particles on the grain boundaries are generally larger than those in the grains. Rare earth oxide particles are mainly spherical and equiaxed;
When the molybdenum lanthanum alloy plate is heat-treated below 1400 ℃, the particle size of La2O3 is very small and difficult to identify. After heat treatment above 1400 ℃, small particles of La2O3 aggregate into larger spherical or short rod-shaped clusters. After 1550 ℃, the size and shape of La2O3 particles change little with the increase of heat treatment temperature.
