Jun 16, 2021
When designing the coating, it is first necessary to understand the service condition of the workpiece and the performance of the surface of the workpiece, and accurately determine the cause of the failure of the workpiece, such as the working medium of the workpiece, the temperature, the nature and size of the force, the material, organization, and size of the workpiece, etc. , So as to determine the requirements for the coating, including bonding strength, hardness, thickness, the number and size of pores, surface accuracy, wear resistance, corrosion resistance, heat resistance or other properties.
 
High temperature oxidation coating
 
High-temperature oxidation resistance refers to the boudoir that can prevent damage to the substrate due to high-temperature oxidation. The melting point of the coating is required to be higher than the working temperature and have a low vapor pressure at the working temperature. The coating is not required to withstand mechanical abrasion. The coating material can be Al, Ni-Cr alloy, Ni/Al wire, etc.
This kind of coating must be resistant to oxidation at ambient temperature. The coating should be as dense as possible. Periodic changes in temperature will affect the thermal fatigue or thermal shock resistance of the coating. The greater the temperature range, the faster the deformation speed, the coating The easier it is to damage, so it is required that the coating and the substrate have a similar coefficient of thermal expansion. Commonly used in exhaust mufflers, annealing pans, annealing hoods, heat treatment fixtures, metal bars, the outer surface of rotary kilns, etc.
 
Gas corrosion resistant coating
 
Gas corrosion resistant coating refers to a coating that can protect the substrate from exposure to high-temperature corrosive gases. It must be considered that when the gas reacts with the coating, it is necessary to prevent the formation of adhering oxides, brittle compounds, or damage to the substrate due to penetration of the coating. This coating is not required to withstand mechanical shock or wear. The coating material can be Ni-Cr alloy, Ni-Cr-Al alloy or Al.
May encounter periodic heating and local hot spots. These are the worst exposed areas. The coating and the base material should have similar thermal expansion coefficients. Commonly used in the end of the plunger, the inner surface of the rotary kiln, brazing fireware, exhaust valve stem, carbonization box, cyanide crucible.
High temperature resistant (above 850℃) erosion coating
 
High temperature resistant (above 850℃) erosion coating refers to a coating that can withstand high temperature and particle erosion. High-speed particles and high-pressure gas at high temperatures create various harsh environments. These coatings must be able to withstand the abrasion caused by moving sharp and hard particles. The coating can be made of pure Al2O3 and stable ZrO2 coating materials. Commonly used in rocket nozzles (nozzles) and missile nose cones.
 
Thermal barrier coating
 
This kind of coating has low thermal conductivity, can be used as a thermal barrier to prevent the base material from reaching its melting point, and also has the effect of transferring radiant heat. The coating can be high temperature oxide coating Al2O3 or CaO, MgO, Y2O3 stabilized ZrO2, etc. General features and requirements:
It must be resistant to oxidation at the working environment temperature. The coating and the base material should have similar thermal expansion coefficients, low vapor pressure, low thermal conductivity, low emissivity and high reflectivity. The lower the emissivity of the coating, the better the thermal insulation performance. The low-density coating is a better insulator and is less sensitive to thermal shock. Commonly used in induction coils of high-temperature furnaces, rocket engine combustion chambers, rocket engine propulsion chambers, brazing and heat treatment fixtures, etc.
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