Hot working method of molybdenum rhenium alloy ingot by electron beam suspension melting
Because of its good room temperature plasticity, high temperature strength and good plasticity after recrystallization, molybdenum alloys are widely used in electric vacuum devices, such as grid insulation screen. Good room temperature plasticity makes deep processing more convenient, such as cutting, drum, deep drawing and so on are much easier than pure molybdenum processing, and it is not easy to appear burr, delamination and cracking. The good high temperature makes the parts not deform and twist when heated to a higher temperature, so as to ensure the normal use of the device, not easy to short circuit, uneven electric field strength fault, to ensure the normal operation of the device. When heated to a higher temperature, the heating element will recrystallize.
When pure molybdenum is used to make molybdenum fabricated parts, when the temperature drops to room temperature after recrystallization, the parts will become brittle and will not be affected by external forces such as vibration and impact. However, the components made of aluminum rhenium alloy can still maintain certain plasticity after recrystallization, and can withstand vibration and impact without fracture, which greatly improves the service life and reliability of components. The MoRe alloy used in high temperature and high vacuum must have low impurity content, especially gas impurity content. Because the gas elements will be released from the alloy at high temperature, which will reduce the vacuum degree of the electron tube, and then affect the electrical properties and service life. In order to obtain high purity molybdenum rhenium alloy with low impurity content, electron beam suspension melting process was adopted. This process has the advantages of high melting temperature, long refining time, sufficient volatilization of impurity elements, no contact between ingot and crucible, and pollution of external impurities avoided. Therefore, molybdenum rhenium alloy ingots with purity ≥ 99.99% can be obtained, which can meet the requirements of electric vacuum application. However, there are always two properties of things. When the purity is improved, the grain size of ingot is very coarse. Sometimes a bunch of grains may grow from one end of the ingot to the other, or even appear the state similar to single crystal.
The present problem is that the ingot can not be processed into products due to large intergranular cracking under external force. In order to solve the problem of hot working cracking, we have tested the stress state and shear slip direction of the material to make the processing process conducive to material deformation, avoid the initiation and propagation of cracks, and obtain qualified plates.
