ISO 4518:2021

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.