There are many kinds of ceramic coatings, such as oxide ceramic coating, carbide, nitride, boron and silicified ceramic coating, intermetallic compound ceramic coating, plastic ceramic composite coating, etc. Among them, cermet coating has been widely used due to its special composition and good comprehensive performance.
Cermet coating is a coating material made of metal and alloy as adhesive phase and ceramic particles as reinforced hard phase through spraying, sintering, agglomeration, coating, and other processes. A series of ceramic powder materials can be made by using different metal and alloy components and proportions and combining with different ceramic powder materials.
With the addition of metal components, the bonding strength between the ceramic coating and the matrix material increases, the adhesion strength between the ceramic particles of the coating increases, the porosity of the coating decreases, and the densification improves. The results show that the ceramic coating has better mechanical properties than the pure ceramic coating, and can be applied to more stress and fatigue conditions and obtain ideal results.
The performance of cermet coating depends on several factors, such as the composition and performance of the metal base, the performance of the ceramic phase, composition, proportion, particle size, etc., the degree of mutual infiltration of the metal base and ceramics, the degree of infiltration of the whole cermet coating and the metal surface, etc. The degree of infiltration determines the adhesion between the various components of the coating and the size of the adhesion between the coating and the metal matrix.
Common cermet coatings are as follows.
Cemented carbide coatings
The cemented carbide coating is made of fine cobalt powder and tungsten carbide sintered, in which cobalt can be replaced by steel matrix, but the resistance to high temperature is decreased. The cobalt-based coating can be used in oil field mud pump plunger, corrugated paper roller, high-speed train brake disc and other applications of abrasion resistance under high temperature. The steel base can be used for cold extrusion die edge incisions.
Tungsten carbide dispersion self-fused alloy coating
The self-fused alloys in such coatings may be nickel, cobalt or iron-based upon performance requirements. The coating is characterized by very tight and high wear resistance and can be used for the various pin, plunger, scraper, and other components.
Coated hard wear-resistant cermet coating
The ceramic powder in the hard wear-resisting ceramic coating is coated with a layer of cobalt and nickel and mixed with the metal base. In this way, the obtained coating avoids the decomposition of some ceramics at high temperature and ensures the consistency and consistency of the coating performance. The nickel-coated diamond coating can be used on diamond grinding wheels and drilling bits. The metal base can also be nickel-aluminum powder and self-melting alloy, which can be sprayed together with tungsten carbide powder to significantly improve the spraying process performance, and is conducive to the production of thin wear resistant coating and reduce the amount of processing.
The coated hard wear-resistant cermet coating is widely used, which can be made into the heat-resistant and high-temperature wear-resistant coating for the high-temperature valve, engine rotor, turbine blade, blast furnace tuyere, and other parts.
Abrasion seal cermet coating
The ceramic phase of attrition seal cermet coating is soft and scratchable non-metallic particles, such as graphite and bentonite. It is a special coating and mainly used in aircraft engines
Anti-friction self-lubricating cermet composite coating
In contrast to the hard wear-resisting cermet coating, the friction-reducing self-lubricating metal-ceramic composite coating uses soft material particles with low friction coefficient, low hardness and self-lubricating performance as ceramic phases, such as graphite, molybdenum disulfide, calcium fluoride, and other solid lubricants. Most of these coatings are used in vacuum applications where liquid lubricants are not available.
High-friction cermet coating
Friction and lubrication are opposite concepts in tribology. Such coatings are generally composite of the multi-component cermet. The metal base includes the copper base, bronze base, iron base, and cobalt base, while the ceramic powder is a mixture of various non-metal particles.
High-friction cermet coating is often used in various types of equipment, motor vehicles on the brake disc, oil field; it can also be used on brake pads of various rotating mechanisms, such as the brake pads of drilling machines.
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