Molybdenum-molybdenum diffusion welding with titanium foil interlayer
Molybdenum is a silver-white metal, with good thermal conductivity, electrical conductivity, low thermal expansion coefficient, low steam, become electronic and electric equipment manufacturing, metal material processing industry, glass manufacturing, high-temperature furnace structural components manufacturing, aerospace and national defense industry applications of important materials. In addition, molybdenum has high corrosion resistance to molten glass, molten salt and molten metal, and is widely used as heating materials and structural materials of high temperature electric furnace, large electrode and grid of vacuum tube, semiconductor and electric light source materials. With the increasingly extensive application of molybdenum foil and the complex shape of structural devices, the effective connection between molybdenum and molybdenum foil matrix is not only of academic value, but also opens up a practical road for the further application of molybdenum foil.
Diffusion connection is a welding method in which the welds are placed in a vacuum or protective atmosphere, under the action of pressure and temperature at the same time, so that the microscopic protrusions on the welding surface produce plastic deformation and achieve close contact, and then form the overall solid connection through atomic diffusion. Due to the relatively high melting point of molybdenum foil, high welding temperature is necessary for vacuum diffusion welding of molybdenum matrix, which is very unfavorable to welding structural parts. In order to achieve welding through atomic diffusion at a low temperature, an interlayer metal with a relatively low melting point is usually added, and the connection is realized through the diffusion of the interlayer metal and the base metal. When Ni was used as the intermediate layer, Mo-Ni was first connected at 900℃, and then Mo/Ni and Al were connected at 550℃ to obtain the best connection strength. When Ti is used as interlayer material, Mo-Al Foil is welded by direct diffusion and the bonding rate reaches 100%. The Ag-Cu-Ti active filler metal was used for vacuum brazing of molybdenum and graphite. The results showed that the Ag-Cu-Ti filler metal formed a good bonding interface with both molybdenum and graphite matrix, and the shear strength of the joint reached more than 80% of that of graphite substrate. The Ni or Ti foil was used as the intermediate layer to connect Mo with graphite by diffusion connection method. The shear strength of the joint exceeded the strength of graphite itself. It can be seen that Ti and Mo have good compatibility. In particular, Ti has strong diffusion capacity and is the most effective active element in active brazing.
