Overview
ISO 4518:2021 - Metallic coatings: Measurement of coating thickness - Profilometric method - defines a profilometric procedure for measuring metal coating thickness by creating a step between coating and substrate and measuring the step height with a profile recording instrument. The standard covers instrumentation, operational parameters, measurement procedure and accuracy considerations for thicknesses from 0.01 µm to 1 000 µm on flat surfaces (and on cylindrical surfaces with precautions). It is particularly suitable for minute thicknesses and for preparing coating thickness reference standards.
Key topics and technical requirements
- Measurement principle
- Form a step by dissolving part of the coating or by masking before coating, then measure step height with a profilometer.
- Instrument types covered
- Contact stylus instruments (surface analysers / profile recorders): traverse 1–100 mm; thickness range ~0.005 µm to 250 µm; height resolution from 0.0005 µm to 1 µm. Stylus tip radii: 2, 5, 10, 50 µm with specified maximum static forces (e.g., 0.7–16 mN depending on tip radius).
- Inductive measuring probes / displacement sensors: typical linearity ≥ 0.5%; measurement range ~1 µm to 1 000 µm; height resolution 0.02 µm to 20 µm.
- Optical profilometers (white‑light interference, confocal, laser‑scanning, chromatic confocal): excellent height resolution (down to ~0.5 nm); measurement range dependent on surface roughness and instrument.
- Accuracy and operational factors
- Profile fidelity, vertical/horizontal magnification, datum alignment, applied stylus force, stylus radius vs surface roughness, vibrations, surface curvature, cleanliness, temperature and calibration.
- Procedure elements
- Preparation of the step, profile recording, thickness evaluation, calibration and reporting requirements.
Applications and who uses it
- Quality control and acceptance testing of electroplated and metallic coatings.
- Production inspection (masking technique) and laboratory validation (dissolution technique).
- Preparation and verification of coating thickness reference standards.
- Typical users: metallurgists, surface metrology labs, coating engineers, QA/QC personnel in automotive, aerospace, electronics, and industrial plating sectors, and manufacturers of precision components requiring traceable thickness measurements.
Practical value
- Enables high‑accuracy thickness measurement across micro- to sub-millimetre ranges with multiple instrument options.
- Advises on minimizing error sources (stylus selection, force control, datum alignment, calibration) to achieve reproducible, traceable measurements.
- Incorporates modern optical profilometry methods in addition to traditional stylus techniques (2021 revision).
Related standards
- Normative reference: ISO 2177 (Coulometric method by anodic dissolution) - useful complementary method for coating thickness determination.
Keywords: ISO 4518:2021, metallic coatings, coating thickness measurement, profilometric method, profilometer, stylus, optical profilometer, confocal microscope, white‑light interference.
