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Understanding Thermal Barrier Coatings (TBCs)

In the realm of high-temperature protection and enhanced turbine engine efficiency, TBCs are at the forefront. These coatings play a pivotal role in safeguarding turbine engines from the detrimental effects of extreme temperatures. In this article, we will delve into the world of TBCs, exploring their significance, applications, and the innovative strides Oerlikon is taking to meet the evolving needs of the aerospace and industrial sectors.

Defining Thermal Barrier Coatings

Thermal Barrier Coatings, commonly referred to as TBCs, are advanced protective layers applied onto the critical components of gas turbine engines. These specialized coating systems serve primarily as thermal insulators, safeguarding turbine engine components from the extreme temperatures and harsh operating conditions to which they are subjected. TBCs typically consist of a yttria stabilized zirconia (YSZ) ceramic coating layer that is applied over an oxidation-resistant metallic MCrAlY bond coat. The primary function of TBCs is to reduce the transfer of heat into the underlying base material, leading to improved mechanical properties and significantly extended component life. This technology has become instrumental in the pursuit of higher efficiency, reduced emissions, and enhanced engine performance of aerospace and industrial gas turbines. Historically, thermal barrier coatings have been plasma sprayed with the Metco 204 yttria stabilized zirconia (ZrO2 8Y2O3) family of powders for ceramic top coats along with our Amdry 386 family of bond coats (NiCoCrAlSiHfY). These notable examples have demonstrated excellent performance for decades. Today, Oerlikon offers vast portfolios of both TBC and MCrAlY powders to meet the needs of its customers.

The Need for Thermal Barrier Coatings

In the constant pursuit of higher efficiency, today's aero and industrial gas turbine engines operate under more stringent conditions, characterized by tighter tolerances, increased pressure ratios, and elevated turbine inlet temperatures. These advancements aim to reduce environmental impacts by lowering NOx and CO2 emissions. However, a significant challenge emerges: while turbine inlet temperatures have risen by a staggering ~500°C (932°F) over the past four decades, the limits of materials used for turbine fabrication have only increased by ~220°C (396°F). As a result, turbine components, and coatings, must now endure temperatures exceeding 1500°C (2732°F). To address this challenge, engineers continue to rely on innovative coating solutions like Thermal Barrier Coatings. Advanced TBCs find application on various critical components such as transition ducts, combustors, heat shields, augmenters, nozzle guide vanes, and blades…to name only a few.

Advancements in TBC Materials

Oerlikon understands that there is no one-size-fits-all solution in the world of thermal barrier coatings. That is the reason why we offer a wide range of materials today, including standard YSZ compositions, high-purity options, and advanced Low-k alternatives with superior thermal insulation properties. We are committed to continuous research and development. By harnessing our in-house Rapid Alloy Development (RAD) materials modeling and simulation tool, while also collaborating with customers and academia, we can pioneer the next generation of material compositions to meet the needs of advanced engine designs. Some examples are products resistant to calcia-magnesia-alumina-silica (CMAS) attack (Metco 6041A), zirconia-based complex oxides with increased service temperature capabilities (Metco 206A), and innovative High Entropy Oxides (HEOs) that are tailored to combine multiple properties (ex. high-temperature phase stability, erosion and CMAS resistance).

Thermal Spray Coating Application Technologies

The coating application process is a critical aspect of TBC effectiveness and performance. Oerlikon has embraced cutting-edge technologies to enhance the efficiency and reliability of the thermal spray process. We develop, offer, and deploy various equipment and application methods including atmospheric plasma spray (APS), vacuum plasma spray (VPS) or low-pressure plasma spray (LPPS), and high-velocity oxygen fuel spray (HVOF). Our innovative cascaded-arc technology, as used in the SinplexPro™ plasma spray torch, offers substantial increases in efficiency, repeatability, and reliability.  This results in significant time and cost savings for coating applicators. In many operations, the time required for TBC coating application has been drastically reduced, leading to fewer work stoppages for maintenance or quality issues. Oerlikon’s leading-edge expertise in developing complete coating solutions enables end users to cost-effectively apply even advanced TBCs which may inherently come with higher material costs and increased application complexities.

Oerlikon's Commitment to TBC Advancements

At Oerlikon, we are dedicated to the continual evolution of TBC systems, thermal spray materials, equipment, and application technologies. In the quest for more efficient and environmentally friendly turbine engines, we are actively exploring customized solutions to meet the ever-changing demands of the aerospace and industrial sectors. Oerlikon's commitment to research and development, coupled with our expertise in developing advanced coating solutions, makes us a frontrunner in the field. Along with our industrial partners, we look forward to the future of sustainable gas turbine engines, made possible by the remarkable world of Thermal Barrier Coatings.