Several main problems in the connection of ceramics and metals

    (1) It is difficult for the solder to wet both ceramics and metals. Most of the conventional brazing filler metal can wet metal, but the ceramics and its composite materials are not wet or have poor wettability, so it is difficult to choose a brazing filler metal that can well wet the two base materials. In recent years, the active brazing filler metal represented by AgCuTi (the active element Ti is added to the brazing filler metal) is capable of wetting ceramics, but it reacts violently on the metal side and easily forms intermetallic compounds. The high temperature performance is not good, and the joint strength is very low when the ambient temperature exceeds 300 ℃.

    (2) A variety of brittle compounds are easily formed at the interface. Since the physical and chemical properties of ceramics and their composite materials are very different from those of metals, in addition to the bond conversion, various chemical reactions are prone to occur during the connection, and various carbides, nitrides, silicides, and oxidations are formed at the interface. And multiple compounds. These compounds have high hardness, high brittleness, and complex distribution, which are the main reasons for brittle fracture of joints.

    (3) There is a large residual stress at the interface. Since the thermal expansion coefficients of ceramics and metals are very different, the joints are prone to residual stress during the connection process and the subsequent cooling process, and the distribution of thermal stress is extremely uneven, causing stress concentration at the bonding interface, resulting in a decrease in the load-bearing performance of the joint.

    (4) It is difficult to quantitatively analyze interface compounds. When determining interface compounds, due to the large quantitative analysis errors of light elements such as C, N, and B, it is necessary to prepare a variety of standard specimens for calibration of each element. For the determination of the phase structure of multiple compounds, X-ray diffraction standard patterns are generally used for comparison, but there is no standard for some new compound phases, which brings great difficulties to the determination of the types and components of the reaction phases.

    (5) The basic data of numerical simulation is lacking. Since ceramic and metal brazing and diffusion bonding, the interface is prone to multi-layer compounds. These compound layers are very thin and have a great impact on the performance of the joint. The lack of room temperature and high temperature data of these phases in the calculation and simulation of interface reaction, reaction phase growth law, and stress distribution brings great difficulties to the simulation calculation.

    (6) There is no reliable non-destructive testing method and evaluation standard. At present, quality control can only be achieved by controlling the macroscopic process parameters (bonding temperature, holding time, bonding pressure), and it is not possible to directly control the connection quality by controlling the interface reaction and interface structure from the microstructure aspect. There is less research on reliability evaluation, lack of credible non-destructive evaluation methods, and no non-destructive testing evaluation standards.

(Huiputech)