Material
Silicon Carbide SiC
The workhorse armor ceramic and the practical middle of the ballistic market: harder and lighter than alumina, cheaper and tougher than boron carbide, and produced domestically at real volume.
Overview
Silicon carbide sits where most armor programs land. Alumina is cheaper but heavy; boron carbide is lighter but several times the price and loses performance against the highest velocity threats. SiC covers the middle with good multi-hit behaviour and a domestic production base that can actually meet volume. Outside armor it does the jobs that need hardness and heat together, from pump seals and bearings to semiconductor process hardware, where its chemical inertness and stiffness matter more than its ballistics. Like every monolithic ceramic it is brittle: it defeats a projectile by shattering it, then needs a composite backer to catch the fragments.
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Defense applications
Body armor strike face
The ceramic front of an ESAPI or SAPI plate. It fractures the incoming projectile; a UHMWPE or aramid backer then catches the ceramic and bullet fragments. Neither half works alone, which is why armor is bought as a qualified plate design rather than as material.
ESAPI and SAPI plates, Side plates, Helmet appliqué, Aircrew armor
Vehicle and aircraft armor
Tiled appliqué over a structural hull, where the tile array is bonded to a backing and the joints between tiles are the design problem. Areal density is the governing number.
Vehicle appliqué arrays, Cockpit shielding, Crew seat protection, Door and hatch armor
Seals, bearings and wear parts
Pump seal faces and bearings in seawater and abrasive service, where the combination of hardness, stiffness and chemical inertness outlasts any metal.
Pump seal faces, Bearings and bushings, Nozzles, Valve components
Semiconductor and optics hardware
Chemical vapour deposited SiC is used for process chamber components and as a substrate for lightweight optical mirrors, where stiffness per unit weight and dimensional stability govern.
Process chamber hardware, Lightweight mirror substrates, Wafer handling components
Alloys and grades
| Designation | Grade | Class | Notes | Typical forms |
|---|---|---|---|---|
| Sintered SiC (SSiC) | Pressureless sintered silicon carbide | Sintered without applied pressure, giving lower cost and free choice of shape at slightly lower density and ballistic performance than hot pressed material. | Armor Tile, Ceramic Component | |
| Hot Pressed SiC (HPSiC) | Uniaxially hot pressed silicon carbide | Densified under simultaneous heat and pressure, producing higher density and better ballistic performance at higher cost and with shape limited to what a press can make. | Armor Tile | |
| Reaction Bonded SiC (RBSiC / SiSiC) | Silicon infiltrated silicon carbide | Formed by infiltrating a porous preform with molten silicon, giving near-net shape with essentially no firing shrinkage. Residual free silicon limits temperature and hardness. | Ceramic Component, Armor Tile | |
| CVD SiC | Chemical vapour deposited silicon carbide | Fully dense, extremely pure SiC grown from a gas phase. The highest purity and best surface finish available, at a cost that confines it to semiconductor and optical work. | Ceramic Component, Optical Window and Dome |
Properties
| Property | Value | Unit | Note |
|---|---|---|---|
| Density | 3.1 to 3.2 | g/cm3 | Roughly 40 percent the density of steel |
| Vickers hardness | 24 to 28 | GPa | Harder than alumina, softer than boron carbide |
| Elastic modulus | 410 to 450 | GPa | Roughly double steel; very stiff for its weight |
| Flexural strength | 350 to 550 | MPa | Strong in compression, comparatively weak in tension like all ceramics |
| Fracture toughness | 3 to 4.5 | MPa m^0.5 | Low. This is the number that makes it brittle and the reason it needs a backer |
| Maximum service temperature | approximately 1600 | degrees C | In inert atmosphere; oxidises slowly in air above this |
| Thermal conductivity | 80 to 150 | W/m-K | High for a ceramic, which is why it resists thermal shock better than alumina |
| Relative cost | Roughly 2 to 3 times alumina | And roughly a third to a half of boron carbide |
Advantages
- Better ballistic mass efficiency than alumina at substantially lower cost than boron carbide
- High thermal conductivity gives good thermal shock resistance for a ceramic
- Chemically inert, including in seawater and most acids
- Very high stiffness per unit weight, useful for optical and structural applications
- Real domestic production capacity at volume, unlike some armor ceramics
- Retains hardness at temperature where metals have softened completely
Limitations
- Brittle, with low fracture toughness; requires a composite backer in any armor application
- Cannot be machined by conventional tooling once fired; needs diamond abrasive throughout
- Sintering shrinkage is large, so near-net forming rarely holds final tolerance
- Multi-hit performance is limited by cracking radiating from the first impact
- Cannot be welded or joined conventionally; requires metallisation and brazing
- Ballistic qualification is per plate design, so a material substitution is not a drop-in
Governing specifications
| Designation | Body | Scope |
|---|---|---|
| MIL-DTL-46593 | U.S. Department of Defense | Projectile, calibers .22, .30, .50 and 20mm fragment simulating. The test projectile behind most armor qualification |
| NIJ Standard 0101.06 | National Institute of Justice | Ballistic resistance of body armor; the governing performance classification for plates |
| ASTM C1421 | ASTM International | Determination of fracture toughness of advanced ceramics |
| ASTM C1161 | ASTM International | Flexural strength of advanced ceramics at ambient temperature |
| Berry Amendment (10 U.S.C. 4862) | United States Code | Domestic sourcing for individual equipment, which captures armor plate |