Learn why cobalt is used in aircraft engines, which hot-section parts contain it, and why nickel or titanium is chosen elsewhere.
Cobalt is used in aircraft engines mainly as part of cobalt-based superalloys and as an addition to nickel-based superalloys. In the engine’s hottest zones, it helps materials retain strength, resist oxidation, hot corrosion, thermal fatigue and wear. It is not used as pure cobalt, nor is it the principal material throughout the engine.
In our Aviation & Real-World Flying coverage, the key distinction is between cobalt-based and cobalt-bearing alloys. A cobalt-based alloy uses cobalt as its matrix metal; a nickel-based superalloy may contain cobalt as one controlled ingredient. The exact composition depends on the alloy grade, component and operating conditions.
What properties make cobalt suitable for jet engines?
Cobalt is valuable because cobalt-rich alloys preserve useful strength and surface durability after ordinary steels and light alloys have lost them.
- High-temperature strength: alloying elements and carbides help the material resist softening and deformation in the hot section.
- Oxidation and hot-corrosion resistance: cobalt works with elements such as chromium and aluminium to form protective surface oxides.
- Thermal-fatigue resistance: combustors and turbine parts repeatedly heat and cool during starts, power changes and shutdowns, creating expansion stresses.
- Wear and galling resistance: cobalt-based hard-facing remains useful on rubbing surfaces, seals and other contact points exposed to heat.
Melting point alone does not explain the choice. Gas-path temperatures can exceed what an unprotected alloy could withstand, so engines combine superalloys with cooling air, protective coatings and carefully controlled component geometry. Combustion chemistry also matters: our guide to avgas and turbine-engine fuel types provides the fuel context, while airborne contaminants such as salt can also contribute to hot corrosion.
Where is cobalt found in an aircraft engine?
Cobalt is concentrated in hot-section and wear-critical parts rather than spread uniformly through the engine.
- Combustor liners, flame holders and related hardware may use cobalt-based sheet alloys.
- Nozzle guide vanes, turbine stator parts and shrouds may use cobalt alloys where thermal fatigue and corrosion resistance outweigh mass.
- Seal lands, contact faces and other wear points may receive cobalt-based hard-facing or coatings.
- Nickel-based turbine blades, discs and other hot-section parts can contain cobalt as an alloying addition.
- Some piston engines use cobalt-bearing hard-facing on exhaust valves, seats or similar high-temperature wear surfaces.
The same material logic applies to the small gas turbine inside an aircraft APU, although its component sizes and duty cycle differ from those of a propulsion engine.
Is cobalt used in turbine blades?
Cobalt may be present in turbine blades, but a modern blade is usually a nickel-based superalloy rather than a cobalt-based alloy.
Rotating blades experience immense centrifugal loading as well as heat. Advanced nickel superalloys generally provide better creep and rupture strength for that job; creep is the slow, permanent stretching of a material under sustained load at high temperature. Cobalt-based alloys are often more attractive for static parts, wear surfaces and components exposed to severe thermal cycling.
| Material | Typical engine use | Main reason for selection | Main limitation |
|---|---|---|---|
| Cobalt-based superalloy | Combustors, vanes, shrouds and wear surfaces | Thermal-fatigue, corrosion and wear resistance | Cost, mass and lower suitability for the most highly stressed rotating parts |
| Nickel-based superalloy | Turbine blades, discs and many hot static parts | Excellent creep and fatigue strength at high temperature | Still requires specialised cooling, coatings and manufacturing |
| Titanium alloy | Fans, compressors and cooler structural areas | High strength relative to weight | Temperature and ignition limits prevent routine use in the hottest gas path |
Does cobalt make an aircraft engine more efficient?
Cobalt does not create thrust or reduce fuel consumption by itself; it helps an engine survive the temperatures and service life demanded by its design.
Higher permissible operating temperatures can support better thermodynamic efficiency, but materials are only one part of the result. Compressor aerodynamics, turbine cooling, bypass ratio, control systems and coatings all contribute. The engine choices behind the A320ceo and A320neo generations illustrate how propulsion improvements come from a complete design rather than one metal.
Why is cobalt not used throughout the engine?
Cobalt is not used everywhere because its heat resistance comes with cost, mass, manufacturing and creep-performance trade-offs.
It offers no weight advantage over nickel and is far heavier than titanium or aluminium. Its supply and price can also be restrictive, while machining, casting, welding and heat treatment require tightly controlled processes. In cooler engine sections, cheaper or lighter materials do the job more effectively.
A common mistake is to treat “cobalt” as a generic hot-section material or replaceable coating. Appearance alone cannot identify an alloy, and an unsuitable repair can cause cracking, coating failure or rapid wear. Engine overhaul therefore uses the approved alloy, filler material, coating and heat-treatment procedure specified for that exact component; grinding or welding also requires controls for metal dust and fumes.