The Role of Plasma Spray Coatings in Increasing Gas Turbine Engine Efficiency

Gas turbines are high-performance machines central to power generation, aviation, and industrial applications. Efficiency and reliability are critical to their operation, as even minor improvements in performance lead to significant reductions in fuel consumption, increased power output, and substantial cost savings.

Plasma Spray Coating is a key method for improving turbine performance, particularly for abradable coatings. In general, there are two main types of coatings used in turbines: hard coatings, which are designed to make surfaces more wear-resistant, and soft, or abradable, coatings. While hard coatings protect parts from wear, abradable coatings are intentionally made soft for specific functions inside turbines.

Material selection and engineering criteria are explored in more detail later in this article.

Plasma Spray and HVOF: Two Different Coating Technologies

Before looking at how plasma spray coatings work in turbines, it helps to know that several types of thermal spray processes are used in industry.

The two most common methods are High Velocity Oxygen Fuel (HVOF) spraying and plasma spraying. HVOF is typically used to create hard coatings, such as Tungsten Carbide, for industrial equipment that requires abrasion and wear resistance. These hard coatings help protect parts from damage.

Plasma spray coatings, in contrast, can be applied to many materials and are well-suited for both hard and soft (abradable) coatings. In gas turbines, plasma spray is often used to create abradable coatings, which serve a different purpose from hard coatings by improving engine efficiency through a controlled wear mechanism.

While both HVOF and plasma spray processes involve thermal spraying, they differ in key parameters. Plasma spraying typically operates at higher temperatures, often exceeding 15,000°C, while HVOF uses lower flame temperatures, generally around 2,500°C to 3,000°C. The particle velocity in HVOF is much higher, usually in the range of 500–900 m/s, compared to plasma spray, which delivers particles at 200–500 m/s. These differences affect the resulting coatings: HVOF produces denser, thinner coatings (often 50–250 microns thick) with low porosity, ideal for hard, wear-resistant surfaces. Plasma spray, on the other hand, can deposit thicker coatings (up to several millimetres) and is better suited for abradable layers that require a specific combination of softness and porosity. The choice between the two methods depends on whether the turbine application requires toughness and wear resistance or a precisely controlled, conformable abradable layer.

The Efficiency Challenge Inside Gas Turbines

Inside a gas turbine engine, there are two primary types of components.

Rotating components include turbine blades, while stationary elements comprise housings or shrouds encasing the blades.

Turbine efficiency depends on the gap between blades and housing. A too-large gap lets air leak, lowering efficiency.

In simple terms, smaller gaps mean better efficiency.

Maintaining small gaps is difficult because blades and housing expand and move under heat and force.

How Abradable Coatings Solve the Problem

Plasma-sprayed abradable coatings play a critical role in resolving clearance management challenges in turbines. According to a 2023 article in Coatings, abradable coatings are designed to be soft enough that they can be easily cut or worn away by the turbine blades, which helps minimise the clearance between the casing and the rotating parts and improves gas turbine efficiency.

How Abradable Coatings Improve Engine Efficiency

Engineers use plasma spray to add a thick abradable layer to the shroud. As the blades lightly touch it, the soft coating is shaped by the motion rather than being damaged by the blades.

This process customises the coating to fit the blade path exactly.

Close Clearance Control (CCL) Coatings

This application is referred to as Close Clearance Control (CCL) coating, as it facilitates consistently precise and minimal clearance within the engine. In practice, engineers optimise the thickness and porosity of the abradable coating to achieve the ideal balance between forming a tight seal and allowing for predictable wear. This optimisation process typically involves a combination of computer simulations, which model airflow and thermal expansion, as well as prototyping and experimental testing of coating samples under operational conditions. Engineers use these methods to assess how different coating formulations respond to blade contact, heat, and pressure and to adjust parameters until the desired performance is achieved. By carefully selecting and validating these properties, designers ensure that the coating conforms to the blade path without risking blade contact with harder underlying surfaces, ultimately maximising efficiency while protecting critical components.

An Everyday Analogy

Imagine applying a deformable, chalk-like layer to the inside of the housing. As it spins, the chalk is incrementally sculpted, leaving an accurately matched groove.

The spinning turbine blades shape the soft coating during engine operation, resulting in a precise gap tailored to the engine.

Protecting Expensive Turbine Blades

Abradable coatings offer an additional technical advantage by protecting turbine blades from wear or impact damage.

Turbine blades handle heat and stress but are complex and costly to make.

If blades hit a hard surface, they can be damaged. A soft coating on stationary parts lets the coating wear away safely instead.

This protective approach extends blade service life and significantly reduces required maintenance and component replacement intervals.

Abradable coatings also prevent fouling from deposits that block airflow and reduce performance. While metallic abradable coatings are widely used in gas turbine engines to improve efficiency by enabling tighter clearances and reducing air leakage, a report from MDPI does not specifically mention General Electric’s LM2500 models or quantify the efficiency gains associated with their use. Other manufacturers, such as Siemens, have also reported measurable gains in fuel savings and durability as a direct result of abradable coatings in their advanced turbine designs. These real-world successes demonstrate how abradable coatings enhance power generation and cost-effectiveness in the energy and aviation industries.

Real-World Impact on Turbine Performance

With tight gaps and blade protection, abradable coatings boost Gas Turbine efficiency. Tighter gaps mean more energy goes to power, so turbines produce more output with less fuel. Small efficiency gains in turbines result in much higher energy output and cost savings in power plants and aircraft.

Tighter gaps mean more energy goes to power, so turbines produce more output with less fuel.

Small efficiency gains in turbines result in much higher energy output and cost savings in power plants and aircraft.

Importance of Plasma Spray Technology

The plasma spray process is fundamental for fabricating specialised coatings, offering precise control over coating properties to meet stringent turbine requirements.

Through meticulous adjustment of composition, thickness, and porosity, plasma spraying enables the production of coatings that balance required softness for blade conformability with sufficient robustness to endure elevated thermal loads. However, these coatings have limitations. Over time, abradable coatings can be affected by erosion from airborne particles, thermal degradation at high operating temperatures, wear from repeated contact with turbine blades, and, in some cases, adhesion failure or cracking during extreme thermal cycling.

To detect and address these issues, engineers routinely inspect turbine components using visual checks, ultrasonic testing, and other non-destructive evaluation techniques. Data from these inspections helps to inform maintenance schedules and identify coatings that need to be refurbished or replaced before failures occur. In addition, advances in coating materials such as the development of more erosion-resistant ceramics or improved binder systems are ongoing to mitigate common failure modes. Understanding these detection and mitigation strategies is essential for engineers to optimise coating design, extend service life, and ensure that coatings continue to perform reliably in demanding turbine environments.

Conclusion

While coatings are conventionally designed for hardness and durability, Plasma-Sprayed Abradable Coatings demonstrate that material engineering can also deliver tailored, application-specific solutions.

In gas turbines, these soft coatings are essential for keeping tight gaps between blades and stationary parts, protecting expensive blades, and preventing air leaks.

These advancements yield improved engine performance, increased power generation, and extended component service life.

As performance demands increase, plasma spray coating technology will remain a core enabler of higher turbine output and efficiency.