Friction coefficients for material pairs and hard coatings, Archard wear calculations, Hertzian contact mechanics, and lambda ratio lubrication analysis. Built for field and lab use.
General material pairs
Approximate values for unlubricated conditions at room temperature. Range reflects surface finish, contamination, and test method variation. Use as starting point only — measure under your actual conditions.
| Material pair | Condition | μ static | μ kinetic | Notes |
|---|---|---|---|---|
| Steel / Steel | Dry, clean | 0.60–0.80 | 0.50–0.70 | Galling risk at high contact pressure |
| Steel / Steel | Lubricated (mineral oil) | 0.09–0.13 | 0.07–0.11 | Boundary lubrication regime |
| Steel / Cast iron | Dry | 0.30–0.45 | 0.20–0.30 | Common in machined components |
| Steel / Bronze | Dry | 0.30–0.40 | 0.14–0.20 | Bronze has natural lubricity |
| Steel / PTFE | Dry | 0.04–0.08 | 0.04–0.06 | Lowest dry μ of common polymers |
| Steel / UHMWPE | Dry | 0.05–0.15 | 0.04–0.12 | Used in bearings and orthopedics |
| Steel / Nylon (PA) | Dry | 0.30–0.40 | 0.15–0.25 | Varies significantly with grade |
| Aluminum / Steel | Dry | 0.55–0.65 | 0.40–0.55 | Adhesion tendency; Al transfer common |
| Rubber / Concrete | Dry | 0.60–0.80 | 0.50–0.70 | Tire-road reference |
| Rubber / Concrete | Wet | 0.40–0.60 | 0.30–0.50 | Aquaplaning risk below ~0.3 |
| Glass / Glass | Dry, clean | 0.90–1.00 | 0.35–0.45 | Clean glass is highly adhesive |
| Wood / Wood | Dry | 0.25–0.50 | 0.20–0.40 | Grain direction and species-dependent |
| Ice / Ice | ~0°C | 0.03–0.10 | 0.02–0.06 | Pressure-induced melt film; temperature-sensitive |
Hard coating tribology
Pin-on-disk values against hardened steel (100Cr6 or equivalent) counterpart unless noted. Coating performance varies strongly with substrate finish, counterpart material, and lubrication. Values are literature ranges for guidance only.
| Coating | Dry air / humid | Dry N₂ / vacuum | Typical hardness | Wear rate (mm³/N·m) | Notes |
|---|---|---|---|---|---|
| TiN | 0.40–0.70 | 0.30–0.50 | ~2200–2500 HV | 10⁻⁶ – 10⁻⁵ | Benchmark PVD coating. Gold color. Adequate tribology; primarily valued for hardness and cost. |
| TiAlN | 0.40–0.70 | 0.35–0.55 | ~2800–3500 HV | 10⁻⁷ – 10⁻⁶ | Superior oxidation resistance (~900°C). Secondary hardening on annealing. Preferred for dry machining. |
| CrN | 0.30–0.55 | 0.25–0.45 | ~1700–2000 HV | 10⁻⁷ – 10⁻⁶ | Best corrosion resistance of the nitrides. Lower μ than TiN. Good for hydraulic and marine applications. |
| CrAlN | 0.35–0.65 | 0.30–0.55 | ~2800–3300 HV | 10⁻⁷ – 10⁻⁶ | Combines corrosion resistance of Cr-based with high-temp stability of Al-based. Excellent for wet machining. |
| DLC (a-C:H) | 0.08–0.25 | 0.003–0.05 | ~1500–3000 HV | 10⁻⁸ – 10⁻⁷ | Friction lowest in dry/vacuum; increases with humidity via OH-passivation of dangling bonds. Best for automotive (dry cam/lifter). |
| ta-C (DLC) | 0.05–0.15 | < 0.01 | ~5000–8000 HV | 10⁻⁹ – 10⁻⁸ | Tetrahedral amorphous carbon. Superlubricity possible in vacuum. Highest hardness, thinnest required (0.5–2 μm). Made by filtered cathodic arc. |
| MoS₂ | 0.06–0.20 (degrades) | 0.01–0.05 | ~200–400 HV | 10⁻⁷ – 10⁻⁵ | Lamellar structure; easy shear between S–Mo–S planes. Oxidizes in humid air → MoO₃ causes friction rise. Ideal for space/vacuum mechanisms. |
| WC/C (a-C:H:WC) | 0.08–0.20 | 0.05–0.15 | ~1000–2000 HV | 10⁻⁸ – 10⁻⁷ | Nanocomposite DLC with WC inclusions. Good performance in both dry and lubricated — less humidity-sensitive than pure a-C:H. Common in automotive injection systems. |
| Al₂O₃ | 0.30–0.60 | — | ~1800–2200 HV | 10⁻⁷ – 10⁻⁶ | Hard ceramic; high wear resistance but brittle. Often used as oxidation-resistant top coat over TiAlN for high-temp interrupted cutting. |
| WC (cemented) | 0.10–0.30 | — | ~1400–1800 HV | 10⁻⁷ – 10⁻⁶ | Substrate or coating material. High stiffness (E ~550 GPa). Co binder content affects both hardness and toughness. |
Calculates wear volume from load, sliding distance, hardness, and wear coefficient.
Elastic contact radius, peak pressure, and deflection under normal load.
Sphere material
Flat material
Ratio of minimum lubricant film thickness to composite surface roughness — determines lubrication regime.