Molybdenum is a silver-white metal with good thermal and electrical conductivity, low thermal expansion coefficient, and low vapor pressure. It has become electronic and electric equipment manufacturing, metal material processing, glass manufacturing, high-temperature furnace structural parts manufacturing, aerospace and defense industry applications Important material. 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 for high-temperature electric furnaces, large electrodes and grids of vacuum tubes, semiconductors and electric light source materials. With the increasing application of molybdenum and the complicated shapes in structural devices, the effective connection between molybdenum and the molybdenum metal matrix not only has academic value, but also opens up a feasible way for the further application of molybdenum.
Diffusion bonding is a welding method in which the weldment is placed in a vacuum or a protective atmosphere, and under the simultaneous action of pressure and temperature, the microscopic protrusions on the welding surface are plastically deformed to achieve close contact, and then the entire solid connection is formed by atomic diffusion. . Because the melting point of molybdenum metal itself is relatively high, the vacuum diffusion welding of molybdenum matrix must require a higher welding temperature, which is very unfavorable for welding structural parts. To achieve welding through atomic diffusion at a lower temperature, an intermediate metal with a relatively low melting point is usually added, and the connection is realized by the diffusion of the intermediate metal and the base metal. With
Nickel or
Titanium box as the middle layer,
Mo and Al were connected by vacuum diffusion welding. When
Ni is used as the intermediate layer, first make Mo-Ni connection at 900°C, and then connect MoNi to Al at 550°C to obtain the best connection strength; when using
Ti as the intermediate layer material, direct diffusion welding of Mo-Al box The welding rate reaches 100%. The Ag-Cu-Ti active solder was used for vacuum brazing of molybdenum and graphite. The results showed that the Ag-Cu-Ti solder and the molybdenum and graphite matrix on both sides formed a good bonding interface, and the shear strength of the joint reached graphite. More than 80% of the base material. With Ni or Ti box as the intermediate layer, Mo and graphite are connected by diffusion bonding method, and the shear strength of the joint exceeds the strength of graphite itself. Diffusion welding of Mo and graphite with Cr and Ni mixed powder with a thickness of less than or equal to 1 mm as an intermediate layer has also obtained good welding strength. It can be seen that Ti and Mo are homogeneous phase diagrams, and the two have good compatibility. In particular, Ti has a strong diffusion ability and is also the most effective active element in active brazing.
Here, 5μm Ti foil is selected as the intermediate layer, and Mo-Mo diffusion welding is carried out under vacuum conditions. The interface morphology, diffusion and interface bonding quality are studied, which lays an important experimental and theoretical basis for the low-temperature diffusion bonding of Mo matrix.
A 5μm Ti box is selected as the intermediate layer, and Mo-Mo diffusion welding is carried out under vacuum conditions. The element composition of the layer area is tested and analyzed, and the interface morphology, diffusion and interface bonding quality are studied.
(1) Under the process conditions of 1000 ℃, 10 MPa, and 60 min, a 5μm Ti foil was added as an intermediate layer to successfully realize the vacuum diffusion welding between the molybdenum and molybdenum substrates, and the welding rate was 100%.
(2) Based on the infinite mutual solubility of Mo-Ti, and the strong diffusion ability of Ti atoms, Mo-Ti solid solution is formed across the thickness of the entire Ti foil, and its composition is close to uniform, and the original Ti layer forms a complete composition close to uniform Mo-Ti solid solution layer.
