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Industrial Gas Turbine (IGT)

Industrial gas turbines play an extremely important role in fields such as energy production. Thermal spraying technology has extensive and crucial applications on industrial gas turbines. On the surface of gas turbine blades, thermal spraying can form coatings that are resistant to high temperatures, oxidation, and corrosion. For example, by plasma spraying ceramic coatings, it can effectively protect the blades from the erosion and corrosion of high-temperature gas, significantly prolong the service life of the blades, and improve the operating efficiency and reliability of gas turbines. At the same time, for components such as the combustion chamber of gas turbines, thermal spraying coatings can also enhance their thermal shock resistance and wear resistance, reduce damage caused by high temperatures, high pressures, and high-speed airflows, lower maintenance costs, and ensure the stable operation of gas turbines.

Thermal Spray Technologies Applicable to Industrial Gas Turbines

Plasma Spray

  • Working Principle:

It utilizes the high temperature generated by the plasma arc to heat the spraying materials to a molten or semi-molten state, and then sprays them at high speed onto the surfaces of gas turbine components to form coatings.

  • Advantages:

It can generate extremely high temperatures and melt almost all materials, including ceramic materials with high melting points. Therefore, it has a wide range of applicable coating materials. For example, thermal barrier coating materials such as yttria-stabilized zirconia (YSZ) are commonly prepared by plasma spray.
The high speed of the plasma flame flow enables the sprayed particles to have a high flight speed. When they impact the component surfaces, they can form dense coatings with high bonding strength, which is beneficial for improving the quality and durability of the coatings. For instance, the ceramic coatings formed on the turbine blades of gas turbines can effectively resist the erosion and corrosion of high-temperature gas.
The process parameters can be precisely controlled, so as to regulate the performance of coatings such as thickness and porosity, meeting the usage requirements of different components.

  • Disadvantages:

The equipment cost is relatively high, and the operation and maintenance expenses are also relatively high. Moreover, it has relatively high technical requirements for operators.

High-Velocity Oxygen-Fuel Spray (HVOF)

  • Working Principle:

Using oxygen and fuel gas (such as propane, propylene, etc.) as fuel, it burns in a high-pressure combustion chamber to generate a high-temperature and high-speed flame flow. The spraying powder is heated and accelerated and then sprayed onto the workpiece surface to form coatings.

  • Advantages:


The flame flow has an extremely high speed, which can make the sprayed particles obtain greater kinetic energy. As a result, the coatings formed have higher density and hardness. For example, the erosion resistance of tungsten carbide-cobalt (WC-Co) coatings prepared by HVOF is significantly improved, and they can effectively resist the erosion of components caused by solid particles carried by the high-speed gas flow in gas turbines.
During the spraying process, the residence time of the powder in the flame flow is short, and chemical reactions such as excessive oxidation are less likely to occur, which is beneficial for maintaining the properties of the coating materials. It has good spraying effects on some alloy materials that are prone to oxidation.
Compared with plasma spray, the cost of HVOF equipment and its operation cost are lower, and the operation is relatively simple.
Disadvantages: The maximum temperature that can be reached is not as high as that of plasma spray. Therefore, the spraying effect on some ceramic materials with high melting points may not be as good as that of plasma spray. Moreover, when spraying large-sized components, there may be problems in controlling the uniformity of the coatings.

Arc Spray

  • Working Principle:

It uses two continuously fed metal wires as consumable electrodes. An electric arc is generated by short-circuiting at the end of the spray gun to melt the metal wires. Then, the molten metal is atomized by compressed air and sprayed onto the workpiece surface to form coatings.

  • Advantages:

The equipment cost is low, the structure is simple, the operation is convenient, and it is easy to maintain. Moreover, the spraying efficiency is high, which is suitable for spraying protective coatings on large-area and large-quantity components. For example, it can be used to prepare protective coatings for large components such as the casings of gas turbines.
A variety of metal wires can be used as spraying materials, such as zinc, aluminum, stainless steel, nickel-chromium alloys, etc. Appropriate materials can be selected according to different requirements for anti-corrosion, wear resistance, etc. For example, for gas turbines operating in a marine environment, aluminum coatings can be applied by arc spray to improve the corrosion resistance of components.
The bonding force between the coating and the substrate is relatively good. It mainly forms a firm protective layer on the component surface through mechanical bonding and metallurgical bonding.

  • Disadvantages:

The porosity of the coatings is relatively high, and its application in some coatings requiring high precision and high density may be limited. In addition, more splashes will be generated during the spraying process, and appropriate protection for the surrounding environment is needed.

Cold Spray

  • Working Principle:

High-pressure gases (such as nitrogen, helium, etc.) are used to accelerate powder particles to supersonic speeds, so that they impact the workpiece surface in a solid state at a relatively low temperature. The combination with the substrate is achieved through the plastic deformation of the particles to form coatings.

  • Advantages:

During the spraying process, the temperature of the powder particles is relatively low, and problems such as oxidation and phase transformation will not occur. The original properties of the materials can be maintained. It has advantages for spraying materials that are sensitive to temperature or need to retain special properties, such as some materials with special magnetic or electrical conductivity.
Relatively thick coatings can be formed, and the internal stress of the coatings is small. Cracks, peeling and other defects are less likely to occur, which is beneficial for improving the reliability and service life of the coatings.
It has a small thermal impact on the substrate and will not cause obvious changes in the structure and properties of the substrate material. It is suitable for some gas turbine components with high requirements for dimensional accuracy and substrate properties.

  • Disadvantages:

The equipment is expensive, the operation cost is high, high-pressure gases are needed as the acceleration medium, and the requirements for the particle size and shape of the powder are strict. The types of available spraying materials are relatively few.

How to choose thermal spraying materials suitable for industrial gas turbines?

Consideration of Working Temperature

    • Selection of Materials for High-Temperature Environments:

The working temperature of industrial gas turbines is usually quite high, especially in the combustion chamber and on turbine blades. For areas with a working temperature ranging from 1000 °C to 1300 °C, yttria-stabilized zirconia (YSZ) is an ideal thermal spraying material. YSZ has excellent high-temperature resistance, low thermal conductivity, and a high coefficient of thermal expansion. After forming a coating on the surface of turbine blades through plasma spraying, it can effectively protect the blades from the erosion of high-temperature gas. This material can maintain a stable structure at high temperatures and prevent the blades from deforming or being damaged due to overheating.
In regions with even higher temperatures, such as the leading edge of the first-stage turbine blades of advanced gas turbines, which may be exposed to high-temperature gas above 1400 °C. In such cases, some new ceramic materials can be considered, such as rare earth zirconates (e.g., La₂Zr₂O₇). These materials have higher melting points and better high-temperature stability, enabling them to withstand extreme high-temperature environments and ensure the safe operation of gas turbines at high temperatures.

    • Materials for Medium and Low-Temperature Areas:

In some medium and low-temperature components of gas turbines, such as the intake part and some cooling channels, the working temperature may range from 400 °C to 800 °C. For these areas, nickel-chromium (Ni-Cr) alloys are commonly used as thermal spraying materials. Ni-Cr alloys have good antioxidant properties and a moderate coefficient of thermal expansion, and they can form stable protective coatings in medium and low-temperature environments to prevent components from rusting and being corroded.

Consideration of Corrosion Environments

    • Materials Resistant to Gas Corrosion:

During the operation of gas turbines, impurities in the gas (such as compounds of sulfur, sodium, potassium, etc.) can cause corrosion to components. To resist this kind of gas corrosion, aluminide coatings are an effective choice. Aluminide coatings, such as aluminum-chromium (Al-Cr) coatings, can be prepared on the surface of components through methods like chemical vapor deposition (CVD) or low-pressure plasma spraying (LPPS). This kind of coating can form a dense aluminum oxide protective film in a high-temperature gas environment, effectively preventing the corrosive components in the gas from contacting the component substrate, thereby extending the service life of the components.
For gas turbines operating in marine environments or environments with high humidity, the requirements for corrosion resistance are higher. In such cases, adopting thermal sprayed ceramic coatings (such as TiO₂ – Al₂O₃ composite coatings) combined with sealing treatment can effectively resist salt spray corrosion and moisture corrosion. This composite coating has good chemical stability and can prevent salt and moisture from penetrating into the coating interior to protect gas turbine components.

    • Materials Resistant to Erosion:

Solid particles carried by the high-speed gas flow in gas turbines (such as dust, sand grains, etc.) can cause erosion on the surface of components. For this situation, tungsten carbide-cobalt (WC-Co) coatings are a good choice. The WC-Co coatings prepared by the high-velocity oxygen-fuel spraying (HVOF) method have high hardness and good erosion resistance. In areas that are prone to particle erosion, such as the leading and trailing edges of turbine blades, this kind of coating can effectively resist the impact of solid particles, reduce component wear, and maintain the performance of gas turbines.

Consideration of the Bonding Performance between Coatings and Substrates

    • Materials with Matched Coefficients of Thermal Expansion:

To ensure that thermal sprayed coatings can firmly adhere to gas turbine components, the coefficients of thermal expansion of the coating materials and the substrate materials need to be well matched. For example, for gas turbine components with a nickel-based superalloy substrate, when selecting thermal spraying materials, it is necessary to consider that their coefficients of thermal expansion are close to that of the substrate. In this case, MCrAlY (where M represents nickel, cobalt, or their combinations) coatings are a good choice. The coefficient of thermal expansion of MCrAlY coatings matches well with that of the nickel-based superalloy substrate. Through appropriate thermal spraying processes (such as vacuum plasma spraying), a good bond can be formed between the coating and the substrate, reducing the phenomenon of coating peeling caused by thermal cycling.

    • Material Pretreatment and Post-treatment for Strengthening Bonding:

Before performing thermal spraying, appropriate pretreatment of the substrate of gas turbine components is a crucial step to improve the bonding performance of the coating. For example, sandblasting treatment can increase the roughness of the substrate surface, thereby improving the mechanical bonding force between the coating and the substrate. After thermal spraying, some post-treatment methods can also enhance the bonding performance of the coating. For example, laser remelting treatment of the coating can make the particles in the coating combine more densely, while also improving the metallurgical bond between the coating and the substrate, further improving the quality and stability of the coating.

Consideration of the Thermal Conductivity of Coatings

    • Selection of Materials for Heat Dissipation Requirements:

In some cooling components of gas turbines (such as cooling blades and cooling channels), it is necessary to select thermal spraying materials with good thermal conductivity to effectively dissipate heat. Copper alloys are materials with high thermal conductivity. By applying thermal sprayed copper alloy coatings, the heat dissipation efficiency of components can be improved. For example, in the internal channels of gas turbine blades cooled by air, thermal sprayed copper alloy coatings can quickly transfer the heat absorbed by the blades to the cooling air, preventing the blades from overheating and ensuring the efficient operation of gas turbines.

    • Materials for Thermal Insulation Requirements:

For the combustion chamber and high-temperature turbine areas of gas turbines, in some cases, it is necessary to adopt coating materials with good thermal insulation properties to reduce the transfer of heat to the interior of components. For example, ceramic thermal insulation coatings with a low thermal conductivity, such as yttrium silicate (Y₂SiO₅) coatings, can be used. This kind of coating can effectively reduce the surface temperature of components, reduce thermal stress, and simultaneously protect the internal material structure of components, improving the reliability of gas turbines in high-temperature environments.

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