Alumina ceramic materials have many excellent characteristics at high temperature, such as high strength, high hardness, high insulation, high corrosion resistance, high wear resistance, good thermal stability and chemical stability. They are ceramic motors, magnetic fluid power generation and nuclear reactions. The key material of the device. When ceramic materials are used in gas turbines or reciprocating engines, such as hoops, turbine blades, valve parts and gas turbine turbocharger parts, their welding technology is particularly important.
Microwave welding is another new method of ceramic welding. Due to its high heating speed and uniformity, it has many potential economic benefits. So far, this technology has been used for the welding of ceramics and ceramics and ceramics and glass.
Ceramic materials have good heat resistance and corrosion resistance, and are playing an increasingly important role in many high-tech fields such as aerospace, automotive, chemical and electronic industries. However, the mechanical processing of alumina ceramic materials is extremely difficult. This greatly limits the further promotion and use of ceramic materials. Solution In addition to the ceramic superplastic forming that is currently being studied, the most promising technology is ceramic welding, which is to weld simple-shaped ceramic parts to make components with complex shapes or large sizes. For this reason, ceramic welding People pay more and more attention. Microwave welding is a brand-new welding technology. It uses microwave to heat the ceramics in the material and completes the connection under a certain pressure. According to whether an intermediate medium is added between the joints, microwave welding can be divided into direct welding and indirect welding. Since the heating of the ceramics is achieved by the interaction of microwaves and materials, the joints can be evenly connected and cracks are avoided. At the same time, the heating speed of microwave heating is extremely fast, the internal ceramic grains will not grow up seriously, and the distribution of grain boundary phase elements is more uniform than before welding, so that the materials in the joint area maintain excellent performance.
Test equipment and characteristics of microwave welding
Typical test device for microwave welding of ceramic materials. The ceramic material to be welded is placed in a microwave applicator, and pressure is applied to both ends of the ceramic material. The microwave generated by the magnetron is transported to the microwave applicator through the microwave waveguide. The microwave frequency is usually 2 45 GHz or 0.915 GHz.
Microwave heating of ceramic materials uses the interaction of microwave electromagnetic fields and ceramic materials, so the microwave heating of ceramic materials has a great relationship with the performance of the ceramic material itself. For ceramic materials that have high dielectric loss and do not change drastically with temperature, the heating process of microwave sintering is relatively stable and easy to control, but most ceramic materials have low dielectric loss at room temperature. When heating exceeds the critical temperature, the dielectric loss of ceramic materials The sharp increase causes the temperature to rise rapidly. In addition, for some ceramic materials that are transparent to microwaves, an appropriate amount of additives or glass phases with microwave absorbing properties must be added to the material to perform microwave heating. Using the dielectric loss of microwave in the material can not only complete the sintering of ceramics, but also realize the connection of alumina ceramic materials. Meek and Black are the first to use microwave technology to realize the glass connection between Al2O3 sheets and the ceramic/glass/metal connection. The main principle of microwave connection of ceramic materials is to realize the focus of microwave energy by changing the distribution of the electromagnetic field, and local and rapid heating of the connection parts, so as to realize the connection of ceramic materials.
There are three characteristics of microwave connection alumina ceramic materials. First, for the traditional ceramic joining process, energy is transferred from the surface of the sample to the inside through thermal conduction, so as to achieve a uniform temperature. Due to the poor thermal conductivity of most ceramics, the connection takes a long time. The use of microwave heating connection makes the ceramic connection layer heat up quickly, thereby greatly shortening the connection time, saving energy and reducing the connection cost. Second, because the microwave heating is relatively rapid and the reaction time is short, the temperature of the connection part can be increased rapidly, thereby inhibiting the internal grain growth of the matrix material due to the increase in temperature, so that the connection part has better mechanics performance. Third, the feature of microwave local heating makes the microwave mainly heat the area that needs to be heated, and the heating of other areas is not obvious. Therefore, the thermal mismatch problem caused by the mismatch of the thermal expansion coefficients of the two base materials in the traditional welding process can be improved to a certain extent.
Microwave applied to the connection of ceramic materials
The microwave connection between ceramic materials can be divided into two types according to whether an intermediate connection layer is used or not. One type is an indirect connection that uses an intermediate medium as a connection layer, such as using Al as a connection layer to connect SiC ceramics and SiC ceramics. The other is the direct connection of ceramic materials, such as the connection of SiC ceramics and SiC ceramics without using a connection layer. According to the type of ceramic base material to be connected, it can be divided into microwave connection between the same kind of ceramic materials and microwave connection between dissimilar ceramic materials.
Ceramic materials play an important role in science and technology, especially high-tech fields, and have broad application prospects. Ceramic connection technology is the key to the wide application of these materials, so it has become one of the research hotspots in the field of materials.