Electron beam vacuum melting is to use the huge local energy of the electron beam (103~106W/cm3) to volatilize impurities (such as phosphorus and aluminum) whose vapor pressure is higher than that of silicon (the vapor pressure of 1700K silicon is 0.0689Pa). Additionally, localized overheating can remove oxides.
The basic principle of the electron beam melting furnace is: in a high-voltage electrostatic field, a high-speed electron beam is bombarded on the metal to be smelted, and the kinetic energy of the high-speed electron beam is converted into thermal energy to achieve the purpose of smelting the ingot. After the cathode is heated to a temperature high enough to emit free electrons under a high-voltage electric field in a high-vacuum environment, a cloud of electrons forms in the space on the surface of the cathode. Under the action of the accelerating voltage, these electrons move to the anode at a very high speed. Through focusing and deflection, the electrons are formed into beams, which accurately bombard the surface of the charge and the molten pool to melt and cool to form crystalline materials. Theoretical calculation and practice have proved that within the range of the operating voltage of the electron beam melting furnace (currently no more than 40kV), the maximum loss caused by X-ray radiation does not exceed 0.5%, and the loss caused by secondary emission is also very small.
In a word, almost all of the energy obtained by the electron beam from the electric field is converted into heat energy. In the range of the electron beam accelerating voltage, the speed of electron movement under the action of the electric field is proportional to the square root of the voltage. Electron beam smelting is generally carried out in a water-cooled copper crucible, and ingot crystallization is characterized by sequential solidification. Electron beam melting can be used not only for smelting rare metals and alloys, superalloys and special steels and other metal materials, but also for smelting non-metallic materials such as ceramics.
Figure 1 is a schematic diagram of the working principle of the electron beam.