Most metals exhibit remarkable heat resistance. But, when exposed to high temperatures for an extended period, they eventually succumb to oxidation and thermal fatigue. This vulnerability is a common cause of metallic component failures in high-temperature environments such as the aerospace and automotive industries.
Thankfully, thermal barrier coatings (TBCs) help to solve this problem. These specialized materials protect metallic components by reducing their heat exposure, making them a key technology in advanced aero engines.
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Among the various TBC materials, advanced ceramics are some of the most preferred options due to their low thermal conductivity and ability to withstand high temperatures better than metals. In the following sections, we explore the application of ceramic materials in thermal barrier coatings.
What is a Thermal Barrier Coating?
A thermal barrier coating is a material that helps reduce a component’s exposure to extreme heat. It forms a protective layer that insulates machine parts from high temperatures.
Typically, thermal coatings consist of materials with heightened temperature resistance, durability, and low conductivity. These features make them remarkably effective in increasing the thermal efficiency of devices and extending the lifespan of critical parts.
Ceramic thermal barrier coatings, in particular, have found extensive applications across various industries, from jet engine turbines in the aerospace sector to automotive exhaust systems and industrial gas turbines.
For example, ceramic coatings applications for automobiles include ceramic car polish production and ceramic car paint protection, among others.
But how do ceramic coatings work? What makes them the preferred thermal barrier coatings choice in most industries?
Why are Ceramic Materials Good for Thermal Barrier Coatings?
Several factors contribute to the heightened preference for ceramic materials in thermal barrier coatings. Below are three key reasons:
High Melting Point
How often do you come across molten ceramics? Probably not so much, because ceramic materials have exceptionally high melting points.
The most typical ceramic thermal barrier coatings, composed of zirconia (ZrO₂) with yttria (Y₂O₃) stabilizers, can withstand temperatures of up to 1200°C–1250°C before even cracking. This far exceeds the capabilities of many metals and polymers.
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The ability of ceramic materials to remain intact at temperatures that would liquefy most metals makes them especially suited to protecting high-temperature engine parts. This makes them perfect TBCs for aerospace shuttle bodies and jet engine turbine fans.
Low Thermal Conductivity
While several metals have high thermal resistance, they are excellent heat conductors, making them prone to high-temperature corrosion.
On the other hand, advanced ceramics are poor heat conductors, a key requirement for efficient performance in aggressive thermo-mechanical environments. Thanks to their low heat conductivity, they don’t experience the thermal expansion stress that occurs with rapid heating and cooling of components.
Additionally, their porosity allows them to adjust to the thermal expansion coefficient of the substrate materials which helps to prevent spalling.
Overall, ceramics’ low conductivity contributes to its ability to keep the substrate’s temperatures low even while exposed to extreme heat.
Oxidation and Corrosion Resistance
Ceramics are inherently resistant to oxidation and corrosion, making them ideal for long-term use in harsh environments.
Chemical reactions occurring due to high heat cause metals to degrade over time in high-temperature environments. This is why some vehicle paint coatings rust or lose their vibrancy when exposed to heat and other harsh environmental effects for a long period.
In most cases, oxidation and corrosion weaken metallic components, compromising their integrity and increasing the risk of failure. But ceramic thermal coating materials, with their inherent resistance to corrosion, can provide remarkable protection against these effects.
By combining these properties, ceramic materials outperform other options, such as polymers or metal coatings, in extreme thermal environments.
To see examples of how ceramic thermal barrier coatings work in the auto industry, check out these Cerakote for Cars reviews.
How are Ceramic TBCs Applied?
Engineers have devised three primary techniques for applying ceramic barrier coatings on machine components. These methods incorporate specialized equipment to ensure optimal performance and adhesion. They are:
Plasma Spray Coating
The plasma spray coating method has the highest popularity rating of all the ceramic TBC techniques. Using this approach, thermal barrier coating suppliers/technicians melt ceramic powders with a plasma torch and then spray the molten particles onto the substrate’s surface.
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This technique helps to create a robust, insulative layer of ceramics on a wide range of materials.
The plasma spray technique demonstrates exceptional bonding and minimal risk of substrate distortion. Despite its high deposition rate, it also guarantees remarkable flexibility in coating thickness.
This method’s versatility makes it applicable across various professional ceramic coating use cases, including auto paint coatings. However, the process requires precise control to achieve uniform coating across the substrate’s surface.
Electron Beam Physical Vapor Deposition (EB-PVD)
EB-PVD involves an almost identical procedure to plasma spray coating. The difference is it uses an electron beam instead of a plasma torch to evaporate the ceramic materials, allowing the vapour to condense on the substrate.
The main advantage of this method is that it produces a columnar structure, which gives the TBC superior thermal fatigue resistance while enhancing its mechanical performance.
However, this technique is often limited to high-value applications due to the high equipment cost and other related expenses. Nevertheless, it guarantees the highest quality ceramic coatings.
Sol-Gel Techniques
The sol-gel technique involves the application of a liquid precursor onto the substrate, which then undergoes drying and heat treatment to create a solid ceramic layer. This emerging TBC application method provides a cost-effective alternative to the other two.
Thanks to its lower cost and ease of use, this technique shows great potential for application in the automotive industry, with various use cases in creating professional-grade ceramic coatings for cars and top ceramic coatings in other industrial machinery.
Additionally, the sol-gel technique’s ability to achieve thin, uniform coatings makes it a promising option for ceramic coatings on windshields.
Final Thoughts
Ceramic materials are redefining the application of thermal barrier coatings. They possess exceptional thermal resistance, durability, and ability to withstand oxidation. These properties make ceramics critical components in industries that require reliable performance in extreme environments.
Advancements in technology will see continuous innovation in ceramic materials and application methods. This will contribute to the greater incorporation of ceramics in automotive paint coatings.