Overview
ISO 18535:2016 specifies a standardized ball-on-disc test method to determine the friction and wear characteristics of diamond-like carbon (DLC) films. The standard defines procedures and guidance for measuring the coefficient of friction and the specific wear rate of DLC coatings when tested under dry conditions in paired contacts (ball vs. disc). Results are not applicable to lubricated operating environments.
Key topics and technical requirements
- Test configuration: Ball-on-disc arrangement (DLC-coated ball / DLC-coated disc / mixed pairs).
- Specimen requirements
- Ball: true sphere (recommended 6 mm diameter), surface roughness ≤ 0.1 µm Ra; sphericity per ISO 3290‑1/2.
- Disc: thickness > 3 mm, flat/parallel within 0.02 mm, test circle ≥ 3 mm diameter, surface roughness ≤ 0.02 µm Ra.
- DLC thickness: 0.01 µm to 10 µm.
- Apparatus & measurement
- Disc rotation drive with stable sliding speed and revolution counter.
- Loading mechanism (weights, lever, hydraulic/pneumatic) to apply controlled normal load.
- Friction measurement accuracy: ±1% of applied load (load cell, spring distortion, torque measurement).
- Optional linear wear measurement sensitivity: 2.5 µm or better.
- Environmental control: temperature ±2 °C and relative humidity 50% ±10 % (or chamber meeting these limits).
- Typical test conditions (friction only)
- Applied load: 3 N
- Sliding speed: 0.05 m/s
- Sliding distance: 200 m
- Key definitions & calculations
- Coefficient of friction μ = friction force / applied normal force.
- Specific wear rate Ws = wear volume V / (applied force F × sliding distance L).
- Specimen preparation & reporting
- Ultrasonic cleaning, solvent rinse, oven drying and storage in test atmosphere.
- Mandatory test report items and repeat counts as specified in the standard.
Applications and who uses it
ISO 18535 is used by:
- DLC coating manufacturers for quality control and comparative performance testing.
- Tribology laboratories and test houses performing friction and wear characterization.
- Materials scientists, R&D teams and component designers evaluating DLC coatings for wear-prone applications (e.g., bearings, sliding contacts, MEMS).
- OEMs specifying test methods for coatings where dry sliding performance is critical.
This method is ideal when application conditions are not fully defined and a repeatable, comparable measure of DLC tribological performance is required.
Related standards
Normative references include:
Keywords: ISO 18535, diamond-like carbon, DLC films, ball-on-disc, friction test, wear rate, coefficient of friction, tribology, coating quality control.
Open preview (PDF)Diamond-like carbon films — Determination of friction and wear characteristics of diamond-like carbon films by ball-on-disc method