Molybdenum and rhenium belong to rare metals, molybdenum rhenium alloy with high melting point and boiling point, very low vapor pressure, high density, high temperature hardness and high temperature strength of many excellent high temperature performance, in metal processing, electronic industry, aerospace and nuclear industry and military and other fields have a very wide range of applications. Molybdenum-rhenium alloy is the main material of fuel rods used in pressurized water reactors. Because molybdenum-rhenium alloy has obvious tendency of brittle fracture at low temperature and produces great thermal stress in the welding process, there are a lot of cracks and pores in the welding joints. For fusion welding process, the welding temperature is too high will lead to the heat affected zone and weld grain coarse, so that the mechanical properties of the joint seriously decreased, if the use of electron beam welding, limited by the vacuum chamber size, welding parts can not be too large, so it is not valuable. Resistance welding and friction welding are not suitable for the complex structure of the workpiece or the fine structure of the workpiece, can not be mass production. However, the solder used in brazing method has a low melting point, which will reduce the high temperature performance of the material itself.
As a solid state bonding method, diffusion welding has incomparable advantages over other welding methods. Diffusion welding is carried out in vacuum, there is no influence of gas impurities on the joint, through the diffusion connection of different components, the product does not need to undergo secondary processing, and can realize the complex structure that cannot be achieved in mechanical processing. At present, the diffusion bonding technology of molybdenum-rhenium alloy is mainly focused on diffusion welding with intermediate layer. However, the introduction of intermediate layer will make the technological process complicated, and the types of intermediate layer materials will also affect the high temperature performance of materials. Therefore, it is of great significance to study the direct diffusion bonding of molybdenum-rhenium alloy.
Compared with fusion welding method, it has many advantages. The fusion welding method is used to impose temperature on a certain point of the weld, which will cause the temperature of the applied position is significantly higher than that of other parts, the temperature distribution is not uniform, the local heat is much, and it is easy to cause residual stress, cracks and other defects. The diffusion welding material is heated in the furnace as a whole, and the temperature distribution is uniform. Therefore, the invention has the advantages of low applied temperature, fewer welding defects (mainly cracks and pores) of joints, and the quality of joints is significantly improved. This indicates that hard second phase metal compounds are produced in the weld, and these second phase structures are helpful to improve the strength and fatigue resistance of the weld. At the same time, the hardness difference between the weld and the base metal is not high, indicating that the hardness and content of the second phase structure are in a more appropriate degree, which will not lead to obvious brittle tendency of the weld, indicating that this welding process can get stable molybdenum-rhenium alloy welding parts.
