November 20th, 2020
Ceramic coatings are a mature technology in the aerospace sector thanks to tandem improvements in both materials and processing capabilities. Technical ceramics can now be deposited as uniform coatings that supplement the underlying substrate. These plasma-sprayed ceramic coatings can offer dramatic improvements to component performance and longevity.
Why Use Ceramic Coatings in Aviation?
Engineers select specific ceramic coatings to add thermodynamic/chemical functionality to base metals that are deployed in challenging conditions. They are usually chosen to improve corrosion-, temperature-, and wear-resistance in afterburners, blades, combustors, nozzle guides, transition ducts, and more. The challenge herein from a processing perspective is how to uniformly coat base parts with high melting point ceramics. Plasma spraying offers a unique solution to this problem.
The Basics of Plasma Spraying
Plasma spray coating is a precision method of depositing a near limitless range of materials onto suitable workpieces. It involves the use of complex integrated equipment including a plasma torch and a powder injector to heat feedstock particles and direct the high-velocity stream onto a relatively cold substrate. This heated flow of ceramic or metallic particles rapidly cools and deposits on the workpiece to form a coating.
The primary advantage of plasma spraying is its ability to deposit materials with extremely high melting points, such as zirconia (2715°C).
Case Study: Plasma Sprayed Zirconia
Yttria-stabilised zirconia, or zirconium oxide, (YSZ) is an ideal material for thermal barrier coatings owing to its low thermal conductivity. The problem, as mentioned, is that the melting point of zirconia prohibits deposition via most thermal spray processes. Plasma spraying provides sufficient thermal energy to melt all materials with reasonably low heat flux on the workpiece.
A typical form of plasma spraying apparatus uses a single electrode pair to initiate ionization of inert gas (argon, nitrogen, etc.) which flows through a constricted nozzle.
Zirconia powder is then fed via a feed line to the extended plasma plume which both heats the particles to the point of melting and propels the molten spray onto the workpiece. The result is a high-performance thermal barrier coating that can mitigate heat propagation from tough working environments to the base metal.
Plasma Sprayed Aerospace Components
Saint-Gobain Coating Solutions is the go-to provider of plasma spraying equipment and thermal spray powders of refractory ceramics for aerospace applications. If you would like to learn about using our feedstock powders or purchasing high power plasma systems for cost-effective thermal spray workflows, simply contact a member of the team today.