C/SiC LSI (LSI / MI)
Matrix · default condition
also Cesic
Choose the liquid-silicon-infiltrated route for the lowest cost and highest density in brake discs, optical structures and mid-temperature hot structures; residual free silicon caps use near 1350 °C.
Values for the LSI condition
Other C/SiC grades and fills
C/SiC is listed in 5 conditions; see the grade overview at C/SiC.
Compare all 5 grades and fillsHide
| Grade · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness |
|---|---|---|---|---|---|
Short/chopped fibre brake grade | Use the chopped-carbon-fibre, silicon-melt-infiltrated brake grade for carbon-ceramic discs and clutch plates: quasi-isotropic, 35 W/m·K and wear resistant, but only 40 MPa tensile. | — | 40 | 0.15 | — |
LSIDefaultThis page LSI / MI | Choose the liquid-silicon-infiltrated route for the lowest cost and highest density in brake discs, optical structures and mid-temperature hot structures; residual free silicon caps use near 1350 °C. | — | 150 | 0.3 | — |
3D woven / needled preform | Pick the 3D woven or needled preform for throat inserts, joints and other triaxially loaded parts, where through-thickness fibres markedly raise interlaminar shear and delamination resistance. | — | 180 | 0.5 | — |
Polymer infiltration & pyrolysis matrix | Use polymer infiltration and pyrolysis for large thin-wall complex parts such as radomes and nozzle extensions; repeated infiltration-pyrolysis cycles leave shrinkage cracks and lower density, 1.9 g/cm³. | — | 220 | 0.4 | — |
Chemical vapour infiltration matrix | Pick chemical vapour infiltration when matrix purity, mechanical performance (300 MPa) and minimal fibre damage matter for aero-engine and rocket hot sections; accept 10–15 % porosity, long cycles and highest cost. | — | 300 | 0.6 | — |
What is C/SiC LSI?
C/SiC LSI is C/SiC in the LSI condition — choose the liquid-silicon-infiltrated route for the lowest cost and highest density in brake discs, optical structures and mid-temperature hot structures; residual free silicon caps use near 1350 °C. C/SiC LSI has a tensile strength of 150 MPa (21.8 ksi), weaker than 57% of composite grades. Elongation at break is 0.3% and the elastic modulus is 65 GPa (9.43 Msi). C/SiC LSI has a density of 2.1 g/cm³ (0.0759 lb/in³), heavier than 78% of composite grades.
Advantages
- High service temperature — 1,350°C (2,462 °F), better than 98% of composite grades
- Good UV / weathering resistance — 100/100, better than 93% of composite grades
- Polishes to a fine finish — 60/100, better than 90% of composite grades
- Conducts heat well — 20 W/m·K (11.6 BTU/hr·ft·°F), better than 78% of composite grades
Limitations
- Limited ductility — 0.3%, worse than 95% of composite grades
- Difficult to machine — 10/100, worse than 91% of composite grades
- High embodied carbon — 45 kg CO₂/kg, worse than 90% of composite grades
- Heavy — 2.1 g/cm³ (0.0759 lb/in³), worse than 78% of composite grades
C/SiC LSI properties
Typical room-temperature values for C/SiC LSI; 11 are specific to this condition. Other listed values are C/SiC reference data and may not represent this condition. Bars are the position among composite grades.
Physical2
C/SiC LSI has a density of 2.1 g/cm³ (0.0759 lb/in³), heavier than 78% of composite grades.
Mechanical10
C/SiC LSI has a tensile strength of 150 MPa (21.8 ksi), weaker than 57% of composite grades. Elongation at break is 0.3% and the elastic modulus is 65 GPa (9.43 Msi).
Thermal6
C/SiC LSI is rated for continuous service to 1,350°C (2,462 °F). It conducts heat at 20 W/m·K (11.6 BTU/hr·ft·°F), better than 78% of composite grades. Thermal expansion is 2.5 µm/m·K (1.39 µin/in·°F).
Electrical1
C/SiC LSI has an electrical resistivity of 0.001 Ω·m.
Chemical & Environmental3
Corrosion resistance is very good (80/100), better than 54% of composite grades. UV resistance is excellent.
Sustainability3
Producing a kilogram of C/SiC LSI takes about 700 MJ of energy and emits 45 kg of CO₂ — more than 90% of composite grades. Typical recycled content is 0%.
Manufacturability2
C/SiC LSI's machinability is not recommended (10/100, worse than 91% of composite grades).
Common Calculations4
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with C/SiC LSI
Is C/SiC easy to machine?
Near-net shaping is the rule. Once densified, only diamond grinding, ultrasonic machining or laser/waterjet cutting is practical; conventional carbide tooling must not be used because it severs fibers and initiates delamination.
Can C/SiC be welded?
Not fusion weldable. Join by silicide brazing, glass-ceramic adhesive bonding, or bolted/pinned attachment to metal parts, matching CTE to avoid thermal-stress cracking.
Can C/SiC be formed, bent or molded?
Form the fiber preform first (weaving, lay-up or needling) and trim it in the green state, then densify by CVI, PIP or LSI. The finished part cannot be reshaped.
What surface finishes work on C/SiC?
CVD SiC coatings or Si-based pore sealing are used to improve oxidation resistance. Optical parts can be SiC-clad and polished to nanometre-level figure; phosphate or glass coatings are applied for emissivity control.
C/SiC chemical composition (wt %)
Limits by weight percent from the governing specification, written the way the spec states them — a single maximum for impurities, a range for alloying elements, and the base element as balance. Nominal is the typical mid-range value.
| Element | Spec limit (wt %) | Nominal |
|---|---|---|
| carbon fiber (PAN/pitch)Volume fraction approx. equals weight fraction; 2D/3D preform | 35 – 55 | 45 |
| free SiResidual free Si only in LSI/melt-infiltration routes | 0 – 20 | 8 |
| residual C matrixUnconverted pyrolytic carbon from LSI/PIP | 0 – 15 | 5 |
| porosityvol%; highest for CVI, lowest for LSI | 1 – 15 | 5 |
| PyC/BN interphaseInterphase layer; determines non-brittle fracture | 0.1 – 2 | 0.5 |
| SiC matrixformed by CVI/PIP/LSI | ≥ 35 (balance) | — |
C/SiC LSI — frequently asked
What is C/SiC LSI used for?
C/SiC LSI is typically used for rocket nozzle liners, re-entry thermal protection panels, high-performance brake discs, turbine engine hot-section components and furnace fixtures. In short: lightest hot-structure CMC; high thermal-shock resistance; brake and nozzle grade.
What is the tensile strength of C/SiC LSI?
C/SiC LSI has a typical tensile strength of 150 MPa (21.8 ksi) — weaker than 57% of composite grades. Strength varies by condition: see the 5 listed tempers.
Is C/SiC LSI easy to machine?
Not especially — machinability is rated not recommended (10/100, worse than 91% of composite grades). Near-net shaping is the rule. Once densified, only diamond grinding, ultrasonic machining or laser/waterjet cutting is practical; conventional carbide tooling must not be used because it severs fibers and initiates delamination.
Can C/SiC LSI be welded?
Not fusion weldable. Join by silicide brazing, glass-ceramic adhesive bonding, or bolted/pinned attachment to metal parts, matching CTE to avoid thermal-stress cracking.
What surface finishes work on C/SiC LSI?
CVD SiC coatings or Si-based pore sealing are used to improve oxidation resistance. Optical parts can be SiC-clad and polished to nanometre-level figure; phosphate or glass coatings are applied for emissivity control.
Can C/SiC LSI be formed, bent or molded?
Form the fiber preform first (weaving, lay-up or needling) and trim it in the green state, then densify by CVI, PIP or LSI. The finished part cannot be reshaped.
What is the maximum service temperature of C/SiC LSI?
C/SiC LSI is rated for continuous use to about 1,350°C (2,462 °F), and briefly to 1,650°C. Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
Sources
- Ceramic Matrix Composites: Fiber Reinforced Ceramics and their Applications (W. Krenkel, ed.) — Wiley-VCH (2008)
- Engineered Materials Handbook Vol. 4: Ceramics and Glasses — ASM International (1991)
- C/C-SiC and Cesic CMC material data — Schunk / ECM (ECM Engineered Ceramic Materials) (2020)
- Cerasep CMC product information — Safran Ceramics (2021)
- SGL Carbon SIGRASIC C/SiC — SGL Carbon (2022)
Property data is compiled from published supplier and standards handbooks and normalised for comparison. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.