Molybdenum has excellent high temperature strength, creep resistance, low thermal expansion coefficient, good thermal conductivity and corrosion resistance, so it is widely used in the electronic industry, aviation and military fields. However, molybdenum has a lower recrystallization temperature, so the use of pure molybdenum is often limited. The recrystallization temperature of molybdenum is about 1000℃. Once the recrystallization of molybdenum occurs, harmful impurity elements are easy to concentrate on the grain boundary, thus reducing the high temperature and normal temperature properties of molybdenum. Like other metals, alloying is beneficial to improve the high temperature performance of molybdenum. Solid solution strengthening and second phase strengthening occur after alloying, which improves the properties of molybdenum alloy. The analysis of the high temperature properties of the representative molybdenum lanthanum alloy and TZM alloy plays an important role in the further development of molybdenum alloy.
After annealing at 1100℃, a small part of grains of molybdenum lanthanum alloy and TZM alloy recrystallized, and with the increase of annealing temperature, the recrystallized grains gradually increased. Different from the pure molybdenum recrystallization structure, the recrystallized grain of molybdenum alloy presents elongated structure, while the recrystallized grain of pure molybdenum is equiaxed grain.
When the annealing temperature is less than 1400℃, the molybdenum lanthanum alloy has strong strength and plasticity. When the temperature is higher than 1400℃, the tensile strength and plasticity are obviously lower. The tensile strength of TZM alloy decreases with the increase of temperature, but the ductility of TZM alloy increases, which is contrary to that of molybdenum lanthanum alloy. In addition, the comprehensive comparison shows that the high temperature properties of TZM alloy are better than that of molybdenum lanthanum alloy at the same temperature.
The thermal brittleness of molybdenum-lanthanum alloy is different from that of TZM alloy when the annealing temperature is higher than 1400℃. The main reason is that the streamline structure of molybdenum lanthanum alloy tends to fracture with the increase of annealing temperature. However, the size, shape and distribution of the second phase of TZM alloy do not change significantly either in the processed state or in the recrystallization state.
