Material
Ceramic Matrix Composite CMC
Ceramic fiber in a ceramic matrix, which survives above 1300 degrees Celsius at a third the density of nickel superalloy. The material that lets a turbine run hotter, and the one most tied to hypersonics.
Overview
Ceramic matrix composites exist to solve one problem: monolithic ceramics have the temperature capability engines need but shatter, because a single crack runs straight through them. Putting ceramic fiber into a ceramic matrix gives the crack somewhere to stop, converting catastrophic failure into gradual damage accumulation. The result is a material that holds structural load above where nickel superalloys melt, at roughly a third the density, and needs far less cooling air. The cost is manufacturing: densifying a preform by chemical vapor infiltration takes repeated cycles measured in days to weeks, which is why CMC parts carry lead times unlike anything else in this atlas and why the qualified supplier base is essentially one company deep.
Supply chain
What feeds what. Click any box with suppliers on file.
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Forms you purchase by the pound or the piece. Each page separates mills from distributors.
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Processes performed on material you already own.
Defense applications
Turbine hot section
Shrouds, nozzles, combustor liners and blade tracks running above the nickel superalloy ceiling. Every degree of turbine inlet temperature bought here converts directly into thrust or fuel burn, and the cooling air saved is air that no longer has to be bled from the compressor.
High pressure turbine shrouds, Combustor liners, Nozzle assemblies, Blade tracks
Hypersonic structure
Leading edges, control surfaces and acreage thermal protection on vehicles where sustained atmospheric flight generates temperatures no metal survives. This is the fastest-growing driver of US CMC investment.
Leading edges, Control surfaces, Thermal protection, Propulsion flowpath structure
Rocket propulsion
Nozzle extensions and thrust chamber components where the alternative is heavy ablative material or actively cooled metal.
Nozzle extensions, Thrust chamber liners, Hot gas valves
Exhaust and signature structure
Exhaust nozzles and aft-end structure where high temperature capability and low weight combine with infrared signature management.
Exhaust nozzles, Divergent flaps, Aft deck structure
Alloys and grades
| Designation | Grade | Class | Notes | Typical forms |
|---|---|---|---|---|
| SiC/SiC | Silicon carbide fiber in silicon carbide matrix | The dominant structural CMC and the one in production turbine service. Fibers and matrix share a chemistry, which avoids the thermal expansion mismatch that plagues mixed systems. | Fiber and Tow, Prepreg, Preform, Laminate and Panel | |
| Oxide/Oxide | Alumina or mullite fiber in an oxide matrix | Inherently oxidation resistant, so it needs no environmental barrier coating, at lower temperature capability than SiC/SiC. Suits exhaust and acreage structure rather than the turbine hot section. | Dry Fabric, Prepreg, Laminate and Panel | |
| Carbon/Carbon | Carbon fiber in a carbon matrix | The highest temperature capability of any structural composite in an inert or short-duration environment, but it oxidizes rapidly in air above roughly 400 degrees Celsius without a coating. | Preform, Laminate and Panel |
Properties
| Property | Value | Unit | Note |
|---|---|---|---|
| Density | 2.1 to 2.8 | g/cm3 | Roughly one third that of nickel superalloy, which is the weight argument |
| Maximum service temperature, SiC/SiC | approximately 1300 | degrees C | Well above the nickel superalloy ceiling; higher with an environmental barrier coating |
| Tensile strength | 200 to 400 | MPa | Modest in absolute terms, but retained at temperatures where metals have no strength at all |
| Fracture behavior | Graceful | Fiber pullout arrests cracks, giving damage tolerance a monolithic ceramic cannot | |
| Residual porosity | typically 5 to 15 | percent | Inherent to infiltration processing; more cycles reduce it but never eliminate it |
| Coefficient of thermal expansion | 4 to 5 | micrometre/m-K | Low, which eases attachment to metallic structure but never eliminates the mismatch |
| Typical manufacturing lead time | Weeks to months | Driven by repeated densification cycles, not by machining or assembly | |
| Environmental durability | Requires coating | Silicon carbide recedes in high pressure steam, so an environmental barrier coating is not optional in a turbine |
Advantages
- Structural capability above 1300 degrees Celsius, well beyond nickel superalloys
- Roughly one third the density of the superalloys it replaces
- Substantially reduced cooling air requirement, which improves engine cycle efficiency
- Graceful damage accumulation rather than the catastrophic failure of monolithic ceramics
- Low thermal expansion and good thermal shock resistance
- Enables sustained hypersonic flight regimes where no metallic option exists
Limitations
- Extremely long manufacturing lead times driven by repeated densification cycles
- Very expensive, with silicon carbide fiber among the costliest structural reinforcements made
- Requires an environmental barrier coating in steam-bearing environments or the matrix recedes
- Residual porosity is inherent to the process and never fully eliminated
- Attachment to metallic structure is a persistent design problem because of thermal expansion mismatch
- Machining requires diamond tooling and is slow and costly
- The domestic qualified supplier base is effectively one company deep
- Non-destructive inspection is difficult, since the material is porous by design
Governing specifications
| Designation | Body | Scope |
|---|---|---|
| ASTM C1275 | ASTM International | Monotonic tensile behavior of continuous fiber-reinforced advanced ceramics |
| ASTM C1341 | ASTM International | Flexural properties of continuous fiber-reinforced advanced ceramic composites |
| CMH-17 Volume 5 | Composite Materials Handbook | Ceramic matrix composites design and analysis guidance |