Overview
ISO 9220:2022 - "Metallic coatings - Measurement of coating thickness - Scanning electron microscope method" specifies a destructive SEM cross‑section method for determining the local thickness of metallic and other inorganic coatings. The method is applicable for coatings up to several millimetres (for very thick coatings ISO 1463 is usually more practical). The standard covers specimen preparation, SEM instrumentation and calibration, measurement procedure, factors affecting results, expression of results, and precision (including round‑robin data in Annex B).
Key topics and technical requirements
- Method principle: Measure coating thickness on polished cross‑section images acquired with a scanning electron microscope (SEM) using the SEM software or external image analysis tools.
- Destructive testing: The specimen is cut, mounted, ground and polished for materialographic examination.
- Instrumentation: Requires a suitable SEM and calibration tools (stage micrometre, graticule, certified patterned silicon, or polymer spheres). Calibration tools should have an uncertainty of less than 5%.
- Calibration: Calibrate the SEM length measurement under the same imaging conditions used for the sample.
- Preparation requirements:
- Cross‑section plane perpendicular to the coating plane.
- Flat surface with entire coating width in focus.
- Remove material deformed by cutting.
- Well‑defined coating boundaries.
- Factors influencing measurement:
- Surface roughness, cross‑section taper (cosine error), specimen tilt, coating deformation, edge rounding, overplating, etching quality, smearing from polishing, poor material contrast, magnification and SEM imaging parameters (acceleration voltage, probe current, brightness/contrast/gamma).
- Magnification guidance: Prefer a field of view about 1.5 to 3 times the coating thickness where practical; use maximum practical magnification for very thin coatings.
- Precision and reporting: Clause 10 and Annex B address measurement uncertainty, repeatability and reproducibility; test report content is specified.
Applications and users
ISO 9220:2022 is used for:
- Quality control and failure analysis of electroplated, deposited or diffusion coatings.
- R&D and materials characterization where local thickness and layer structure must be resolved at high spatial resolution.
- Certification and acceptance testing when destructive cross‑section measurements are required.
Typical users:
- Materials laboratories, coating manufacturers, surface engineering and metallography labs, automotive/aerospace component inspection teams, and academic researchers.
Related standards
- ISO 1463 - Microscopic (light microscope) method for coating thickness (recommended for very thick coatings).
- ISO 2064 - Definition reference for local thickness (terminology used in ISO 9220).
- SEM imaging and EDS guidance referenced in the standard’s bibliography and Annexes.
Keywords: ISO 9220:2022, coating thickness measurement, SEM method, scanning electron microscope, metallic coatings, cross‑section preparation, calibration, measurement uncertainty.
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