Heat resistant and oxidation resistant coating

1. High temperature oxidation coating
Resistance to high temperature oxidation is to prevent the matrix due to high temperature oxidation damage caused by the Buddha. The melting point of the coating is required to be higher than the operating temperature and to have a low vapor pressure at the operating temperature. The coating is not required to withstand mechanical wear. Al, Ni-Cr and Ni / Al wires can be used as coating materials.

Such coatings must be resistant to ambient temperature oxidation, the coating should be as dense as possible, the temperature cycle will affect the coating thermal fatigue resistance or thermal shock resistance, the greater the temperature range, the variants faster, coating The more easily damaged, so the coating and the substrate requires a similar thermal expansion coefficient. Commonly used in exhaust muffler, annealing plate, annealing hood, heat treatment fixture, metal bars, the outer surface of the rotary kiln.


2. High temperature gas corrosion coating
A gas-resistant coating is a coating that protects the substrate from exposure to high-temperature corrosive gases. It is necessary to take into account that the gas reacts with the coating to prevent the formation of adherent oxides, brittle compounds, or destruction of the matrix due to the permeation of the coating. Such coatings are not required to withstand the effects of mechanical impact or wear. The coating material may be Ni-Cr alloy, Ni-Cr-Al alloy or Al.

May experience periodic heating and local hot spots, which are the worst exposed areas, and the coating and matrix materials should have similar thermal expansion coefficients. Commonly used in the plunger end, rotary kiln internal table, brazing firearms, exhaust valve stem, carbonization box, cyanide treatment crucible.


3. High temperature (above 850 ℃) erosion coating
High temperature (more than 850 ℃) Erosion coating is resistant to high temperature and particle erosion of the coating. At high temperatures, high-speed particles and high-pressure gas form a variety of harsh environments. These coatings must be able to withstand the movement of the sharp particles caused by wear and tear, the coating can be used pure Al2O3 and stable ZrO2 coating material. Commonly used in rocket nozzles (nozzle), missile nose cone.


4. Thermal barrier coating
This coating has a low thermal conductivity, can be used as a thermal barrier to prevent the matrix material to reach its melting point, also has the role of transfer of radiant heat. Coating can be coated with high temperature oxide Al2O3 or CaO, MgO, Y2O3 stable ZrO2. General characteristics and requirements:

The coating and the substrate should have similar coefficient of thermal expansion, low vapor pressure, low thermal conductivity, low emissivity and high reflectivity at the operating ambient temperature. The lower the emissivity of the coating, the better the thermal insulation, the lower the density of the coating is a better insulation, but also the thermal shock sensitivity is small. Commonly used in high-temperature furnace induction loop, rocket engine combustion chamber, rocket engine room, brazing and heat treatment fixture.