Metals and their alloys are widely used in ship corrosion protection, especially in direct contact with the external seawater, as corrosion resistant and structural materials with toughness and toughness requirements. In addition, metals and alloys are also used in ships as important coating materials due to their superior corrosion resistance and wear resistance.
With the improvement of the application requirements of ship materials, composite materials came into being, among which the metal-ceramic materials with high-temperature resistance, excellent corrosion resistance, and wear resistance was born. In recent years, metal ceramic materials have been gradually applied to engines and internal combustion engines with high temperature, corrosion resistance, and other requirements, which have special requirements for thermal and mechanical properties. Metal-ceramic composites not only have excellent corrosion resistance but also inherit the toughness of the metal. The double properties of high-temperature resistance of ceramics make the metal-ceramic composites widely favored.
Metal alloy coating
As the modern ship industry puts forward higher requirements on temperature and pressure, metal and alloy coatings are increasingly favored. The study of the metal protective coating was officially started after 1960, and the first subject studied was M-Cr-Al-Y. With the development of research, the industrialization of this product has become a reality, and it has been widely accepted and applied for its excellent high-temperature resistance and corrosion resistance.
At present, the most widely used coating is cobalt-nickel cesium aluminum alloy, which not only has the fine character of the metal and its alloy but also has the composition control, the stable material itself property and the coating contact interface. It is able to form stable oxides at high temperatures, such as alumina, which is conducive to the preservation of the protected material.
The material itself is easy to adjust the composition of the metal alloy according to different needs to improve the performance of the coating. There are various ways to improve the metal coating. In addition to the composition adjustment method mentioned above, the order of action of the alloy can be controlled by controlling the diffusion method to meet the requirements of aerospace or other aspects for metal alloy. The improvement method of metal coating also includes process improvement, which can provide space for the coating to meet service performance. However, with the further improvement of the coating application requirements of ship materials, the metal and alloy coating obtained by the above methods can hardly meet the actual requirements. Therefore, it is very urgent to develop a new type of coating material with good resistance to high temperature and corrosion.
With further research on the coating, people no longer limited to the research on the coating itself, but take the ship material and coating as a systematic research object. The reason is that the application of hull materials and their interaction should be considered in the study of coatings so that the functional and environmental requirements of ship materials can be taken into account. Ceramic coatings can be studied independently without considering matrix due to their special composition, so people began to study the ceramic coating with good corrosion resistance and can realize the separation of the matrix.
Ceramic coating has many excellent characteristics, such as high hardness, high chemical stability, high corrosion resistance, etc. Ceramic coating is free from the limitation of matrix research and can be studied as a single individual without affecting its performance and without being restricted by matrix size, all of which are properties that are difficult for ordinary coating materials to possess. However, ceramic materials also have their disadvantages. If they are not as tough as metal materials, they will easily flake off with ship deformation or collision after being coated on the substrate.
Metal-ceramic composite coating
The common metal alloy coating on the surface of ships is easy to cause the coating to fall off due to friction, potential corrosion, and seawater corrosion, thus losing the effect of the coating. Besides the toughness of the metal, the metal-ceramic coating also has the chemical inertia of the ceramic itself, which can effectively prevent the corrosion caused by seawater and potential.
The major factors affecting the corrosion resistance of the metal-ceramic coating include the proportion of doped elements in the material and the thickness of the bond layer. For example, the bond thickness can significantly affect the corrosion resistance of ship materials, and cobalt-nickel alloy can alleviate the problem of coating rupture caused by stress concentration at the optimal thickness. With the deepening of the research, the optimal transition layer thickness has been gradually deduced. This transition layer can not only alleviate the peeling of the coating caused by excessive stress concentration but also can supply internal and external elements and play a role of corrosion resistance. The choice of doping elements lies in the actual demand for ship materials, and the composition adjustment of the metal-ceramic coating according to the actual demand can realize various functions of ship materials.
It is worth mentioning that the research proves that the metal-ceramic coating with excellent performance is not a simple two-layer coating, but a mechanical property combination that takes full account of stress, composition, heat insulation performance, corrosion resistance, and other factors.
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