Molybdenum and its alloys
Molybdenum and molybdenum alloy is a kind of high temperature resistant material, can maintain high strength at high temperatures. At the same time, it also has high thermal conductivity and low thermal expansion coefficient, and good heat shock resistance. The material also has good electrical conductivity and wear resistance. Due to the above advantages, molybdenum and molybdenum alloys are widely used in the aerospace field, including molybdenum foils for interconnecting solar arrays of space vehicles (satellites, spacecraft and space stations). However, the weldability of molybdenum is relatively poor and will be strongly oxidized at high temperature, this oxide film has no protective effect, and for the space vehicle solar panel interconnecting material, good weldability and electrical conductivity is indispensable. In order to solve the problem, the surface of molybdenum needs to be modified by electroplating. Because silver has good brazing properties, silver is usually plated on the surface of molybdenum to improve weldability and reduce or prevent oxidation of molybdenum.
Since there are often natural oxides on the surface of molybdenum, mainly MoO3, this oxide will interfere with the adsorption of the coating. At the same time, the formation of an alloy (solid solution) between molybdenum and silver is very difficult, the reason is that molybdenum in silver solubility is very small, at 1600℃, molybdenum in silver solubility is only about 5%, the current market of AgMO30, AgMo50, AgMo65 and AgMo75 and other alloys are sintered by powder metallurgy method. Therefore, it is difficult to electroplate silver on the surface of molybdenum, and direct silver plating often does not adhere well, and the coating quality is poor. The solution to the difficulty of molybdenum plating silver is generally to use the method of pre-plating or impact plating on the surface of a thin layer of metal (such as chromium, nickel, gold, rhodium, platinum, etc.), after high temperature heat treatment and then continue plating, the process is more cumbersome, silver plating and molybdenum foil combination is not good.
Metal plasma injection modification technology is a surface treatment technology developed in the 1980s. It is to directly inject metal ions into the material that needs to be modified to obtain a metal modified layer with no obvious interface and high bonding strength, and improve the surface conductivity. At the same time, the ion beam also has a bombardment effect on the surface of the material during the injection process, which can often remove the oxide on the surface of the material. On this basis, the electroplating of the material can be obtained with good quality and high bonding strength. Obviously, metal plasma injection technology can solve the problems of silver plating on the surface of molybdenum foil, including the existence of natural oxides on the surface of molybdenum foil and the difficulty of forming a solid solution of silver molybdenum.
