Wetting phenomenon of metal ceramics
Wetting is the process by which a gas on a solid surface is replaced by a liquid. In metal-ceramic systems, when a molten metal droplet comes into contact with a ceramic substrate, a flat droplet of a certain shape is formed on the surface of the substrate depending on the properties.
Non-reactive wetting
No chemical reaction occurs during the interfacial wetting process, and the driving forces of the wetting process are only diffusion and van der Waals forces. The surface tension of the liquid metal is the main thermodynamic parameter that determines whether the liquid metal can be wetted on the surface of solid-phase ceramics.
The wettability of non-reactive wetting systems is generally poor, but the process proceeds quickly. The non-reactive wetting system can complete the wetting process in about 10-3 s. Therefore, the influence of the holding temperature and holding time on the wettability of the system is very small, and the main thermodynamic parameters that determine the wettability are the surface tension, gravity and viscosity of the liquid metal.
The metallicity of the ceramic, crystal orientation and the content of alloying elements in the metal liquid have a great influence on the wettability of the system.
Reactive wetting
Reactive wetting is mainly divided into redox wetting and dissolution wetting. Redox wetting process will occur at the interface to generate interfacial reaction products, thus improving the wettability of the system. Representative metal-ceramic systems include Cu-Si/Cv, Al/TiC, Al/SiC, AgCuTi/Al2O3 and TiB2.
Along with the interfacial chemical reactions, the main parameters affecting the wettability of metal/ceramic systems during the wetting process are the interfacial products and their chemical properties. Redox wetting generates new interfacial products at the metal/ceramic interface, allowing the liquid metal to be wetted at an interface that is more affinity to it, thus improving the wettability of the metal-ceramic system.
The increase in holding time, the addition of alloying elements, and the increase in holding temperature during redox wetting generally improve the wettability of the metal-ceramic system.
