At Metallisation, we work with plasma spray systems that support demanding industrial needs across aerospace, energy, engineering and manufacturing. This article explains how plasma spray works, step by step, in clear and simple terms.
What Is Plasma Spray?
Plasma spray is a thermal spray process that uses a high temperature plasma jet to melt coating material. The molten particles are sprayed onto a prepared surface, where they cool and form a solid coating. Plasma spray can process metals, ceramics and composites that other spray methods cannot easily melt.
Why Use Plasma Spray?
Plasma spray is often used when standard coating methods cannot meet performance demands. It suits applications where parts face high temperatures, heavy wear or aggressive environments – for example, in the aerospace, medical, automotive and power generation sectors.
Plasma spray works well on complex shapes and critical components. The short heat exposure reduces the risk of distortion, which is important for precision parts.
The Science Behind Plasma Spraying
Plasma is often called the fourth state of matter. It forms when gas is heated to very high temperatures and becomes electrically charged. In plasma spray, this ionised gas reaches temperatures above 10,000°C. This intense heat melts the spray material almost instantly. The molten particles are then accelerated towards the surface at high speed, where they flatten and solidify to form a coating.
So what are the steps involved? Let’s take a look.
Step 1: Preparing the Component
As with all thermal spray coatings, surface preparation is critical. The surface must be clean, dry and free from oil, grease or oxidation. Grit blasting is used to roughen the surface and create a mechanical key. This textured surface allows the molten particles to anchor securely when they impact the part.
Step 2: Selecting the Spray Material
Plasma spray uses powder feedstock rather than wire. The powder choice depends on the coating purpose. Common materials include alumina, zirconia, chromium oxide, tungsten carbide and metallic alloys. Ceramic powders are often used for thermal insulation and electrical resistance, while metallic powders are used for wear and corrosion protection.
The powder size and flow rate are carefully controlled to achieve a stable spray and even coating.
Step 3: Generating the Plasma Jet
Inside the plasma spray gun, an electric arc forms between a cathode and an anode. A process gas (often argon with hydrogen or helium) flows through this arc. The gas becomes ionised and forms plasma. This plasma exits the nozzle as a high-velocity jet with extreme heat.
Unlike arc spray, plasma spray requires high electrical power and precise gas control to operate correctly.
Step 4: Injecting the Powder into the Plasma
The coating powder is injected into the plasma jet, either internally or externally. As the powder enters the plasma, the particles heat up rapidly. Most particles melt fully, while some may become semi-molten depending on material and settings. The plasma jet accelerates these particles towards the surface at very high speeds.
Step 5: Spraying the Molten Particles onto the Surface
The operator holds the plasma gun at a controlled distance and angle. When the molten particles strike the surface, they flatten into thin discs called splats. These splats cool almost instantly and bond mechanically to the roughened surface. As the spray continues, layers build up to form the full coating.
The base material remains relatively cool because the heat exposure time is very short.
Step 6: Building the Coating Structure
Plasma spray coatings are built up through multiple passes. Each pass adds thickness and density. Typical coating thickness ranges from 50 microns to over 1 millimetre, depending on the application. Ceramic thermal barrier coatings are usually thinner, while wear coatings may be thicker.
The coating structure can be tailored by adjusting spray distance, power level and powder feed rate.
Step 7: Cooling and Finishing
Once spraying is complete, the coating cools naturally. Some coatings require post-spray finishing. This may include grinding or polishing to achieve a smooth surface or precise dimensions. Certain coatings may also need sealing to limit porosity and improve resistance to fluids or gases.
What Are the Key Benefits of Plasma Spraying?
- Plasma spray can process materials with very high melting points. This makes it ideal for ceramic coatings that resist heat and electrical current.
- It also produces dense coatings with strong adhesion. The process allows precise control over coating thickness and structure.
Typical Uses
Aerospace
Used to apply thermal barrier coatings on turbine blades and engine components.
Medical
Used to coat implants with biocompatible materials such as hydroxyapatite.
Power Generation
To help protect components exposed to heat and erosion.
Manufacturing
Used to protect rolls, shafts and seals from wear.
Safety and Good Practice
Plasma spray uses high voltage, intense heat and fine powders. So proper safety practices are essential. Operators must wear protective clothing, eye protection and respiratory equipment. Spray booths need good ventilation and dust extraction. Regular maintenance and training are critical for stable operation and repeatable coating results.
The Final Finish
Metallisation has become the UKs leading developer, manufacturer and worldwide supplier of a full range of metal spraying equipment – providing high quality plasma spray systems, since 1922. If you’ve got a project you need help with, simply contact us today and we’ll be more than happy to help.