Application of welding ceramics
With the development of science and technology, fundamental changes have taken place in the composition, performance, manufacturing technology and application fields of welding ceramics. At the same time, due to its unique high temperature performance, wear resistance and corrosion resistance, etc., it has become Important materials for high-tech products such as magnetic fluid power generation and nuclear reaction devices have developed from traditional living ceramics to functional ceramics with special properties and high-performance engineering ceramics, which have played an important role in electronic information technology; but due to its Severe brittleness makes it impossible to manufacture complex and impact-resistant parts. Let's learn about the application of welding ceramics together !
1. The importance of welding ceramic technology
Whether it is welding ceramic to metal welding or welding ceramic to ceramic with metal filler materials, the bonding of the ceramic to metal interface is problematic. It is very difficult to realize the metallurgical bonding of the interface between ceramics and metals; due to the obvious differences between ceramics and metals in the crystal structure, mechanical properties, thermophysical properties and chemical properties of the electronic team, in the usual welding materials and processes, it is almost impossible to to reliable connections, especially fusion welding.
1) The problem of interface reaction Whether it is diffusion welding or brazing, the bonding mechanism of ceramic/metal interface is chemical bond. In order to obtain a good interface bonding during diffusion welding, the metal must also be active to the ceramic. According to the thermodynamic conditions, the selection principle of the active element is based on the free energy change g0 of the reaction with the ceramic.
2) Thermal-mechanical matching problem on both sides of the interface. Due to the large difference in thermal expansion coefficient between ceramics and metals, the metal used as the intermediate layer has a metal yield point s with a small thermal expansion coefficient and a soft metal with a low elastic modulus e. Cooling at the welding temperature will generate a lot of thermal stress, which will reduce the fracture strength of the joint and even crack. The current main solution is to add an intermediate layer between ceramics and metals, however, the two are usually at odds.
3. Comparison of several welding methods
The previous analysis shows that fusion welding is not suitable for ceramic welding. Solid phase diffusion welding and brazing are suitable for welding ceramics,
4. Development prospects of welding ceramics
There are a lot of studies on ceramic welding. At present, in addition to more in-depth research on theoretical issues such as interface reaction and numerical simulation of internal stress, it will also focus on practical applications. Its main problems are as follows
1) In order to give full play to the high temperature resistance of ceramics, it is necessary to solve the high temperature performance of the joint.
2) The current tests use small samples. The front cracks and low stress damage of ceramics are serious problems. It is necessary to further study the method of reducing internal stress. The problem of internal stress is not too prominent. In the case of large-area and complex parts welding .
3) The current welding of ceramics is mainly carried out in vacuum, which has low efficiency and high cost. It is necessary to study non-vacuum low-cost welding methods.
The above is the application of welding ceramics , and the reliability evaluation of ceramics for welding is also an important issue. Since ceramics are brittle materials, brittle fractures in service are very dangerous if they contain welding microcracks and internal stress levels are too high.