Preparation process of molybdenum/palladium/silver layered metal matrix composites. The steps are pretreatment of molybdenum metal foil, molybdenum metal surface electroplating palladium, annealing of molybdenum/palladium electroplating sample, dehydrogenation treatment, molybdenum/palladium layer annealing of silver electroplating surface of dehydrogenation sample and pressure annealing of molybdenum/palladium/silver electroplating sample, scanning electron microscope observation of cross section morphology of molybdenum/palladium/silver layered metal matrix composite material and resistance spot welding tensile strength test. The present invention diffuses the molybdenum/palladium and palladium/silver interfaces, thus realizing metallurgical bonding on the molybdenum/palladium and palladium/silver interfaces, and obtains the molybdenum/palladium/silver lamellar metal matrix composite material with good weldability and high interface bonding strength.
Although platinum has strong chemical stability and oxidation resistance, it is too expensive to produce molybdenum/platinum/silver laminated composites and use in space vehicles. Due to the similar properties of the same platinum group metals, and molybdenum in palladium metal has a high solid solubility (molybdenum in palladium at 1600°C solid solubility reached about 46%atm, at room temperature molybdenum in palladium solubility can also reach about 20%atm), molybdenum and palladium are not easy to form brittle intermetallic compounds at room temperature. At the same time, when palladium and silver are alloyed, discontinuous mutual solubility between components can be produced. Therefore, palladium metal is tried to replace platinum metal as the intermediate layer metal to prepare lamellar composite materials, namely molybdenum/palladium/silver lamellar composite materials.
The preparation of metal matrix composites usually requires multiple high-temperature annealing, which may involve hydrogen protection annealing, and palladium metal is more sensitive to hydrogen. Mainly at room temperature, 1 volume of spongy palladium can absorb 900 volume of hydrogen, and 1 volume of colloidal palladium can absorb 1200 volume of hydrogen. The bulk metal palladium can absorb more hydrogen, and the volume will expand significantly, become brittle and even break into fragments. This brings great difficulty to the preparation of molybdenum/palladium/silver layered composites. In addition, the thermal expansion coefficient of palladium is greater than that of molybdenum (molybdenum's thermal expansion coefficient is about 5.2 '10-6/K-1, palladium's thermal expansion coefficient is about 11.0' 10-6/K-1), and the thermal stress of molybdenum/palladium interface is easy to be too large during annealing, which leads to the destruction and delamination of molybdenum/palladium interface, which also makes the yield of molybdenum/palladium/silver laminated composite difficult to control. This is also the reason why molybdenum/palladium/silver laminated composites have not been made for many years.
