DLC puts a 1–3 µm layer of amorphous carbon on the surface: harder than any steel, with friction close to PTFE, and thin enough to leave the tolerance alone.
| Thickness | 1–3 µm |
|---|---|
| Hardness | 2000–4000 HV |
| Friction | 0.05–0.15 against steel, depending on hydrogen content and humidity |
| Max service temperature | ≈300 °C (some grades 400 °C) |
| Process temperature | <200 °C — no effect on a hardened substrate |
| Effect on dimension | Minimal — 2–6 µm across a diameter |
| Typical use | Raceways, sliding surfaces, fuel and injection components, cutting tools |
DLC is a thin film of amorphous carbon with a mixture of sp2 and sp3 bonds. The sp3 fraction gives diamond-like hardness; the hydrogen content and the doping control friction and residual stress. Because it is deposited at low temperature, it can be applied to a finished, hardened bearing ring without altering its heat treatment — unlike a nitride or a chrome deposit.
The catch is thickness. At 1–3 µm, DLC cannot carry load on its own: if the steel beneath yields, the coating cracks and flakes. DLC is a surface treatment for surfaces that are already strong enough, which is why it goes on hardened raceways and not on soft ones.
| Property | DLC | Thin dense chrome | Mn phosphate |
|---|---|---|---|
| Thickness | 1–3 µm | 2–10 µm | 5–15 µm |
| Hardness | 2000–4000 HV | 800–1000 HV | Soft, crystalline |
| Friction | 0.05–0.15 | 0.10–0.20 | Lowers during running-in |
| Max temp | ≈300 °C | ≈300 °C | ≈200 °C |
| Process temp | <200 °C | ≈50–60 °C bath | 85–95 °C bath |
| Relative cost | High | Moderate | Low |
Hardened raceways where friction and wear both matter.
Read →Where the film is thin and scuffing risk is real.
Read →A thicker, cheaper alternative for wear and corrosion.
Read →Long-life joints with restricted lubrication.
Read →By 1–3 µm per surface, so 2–6 µm across a diameter — usually inside the tolerance, but it must be stated on the drawing.
Yes. It is deposited below 200 °C, so a hardened and ground ring is not affected. The bearing must be disassembled, coated and reassembled, which is why it is a high-value-part treatment.
Adhesion failure: insufficient surface preparation, a substrate that is too soft and deflects, or residual stress in a thick film. A thin interlayer is often used to improve bonding.
It is one of the better options, but its friction rises in very dry air and it has limited life once the film wears through. For permanent dry running, a PTFE composite or a ceramic bearing is usually more robust.
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