Overview
ISO 26423:2009 specifies the crater-grinding method for determining the thickness of ceramic coatings on fine/advanced ceramics (advanced technical ceramics). The method produces a spherical crater by rotating a ball wetted with an abrasive slurry against the coated surface. Coating thickness is calculated from measured crater dimensions and the ball radius. Note: the test is not suitable when surface roughness of the coating or substrate exceeds 20% of the coating thickness.
Key topics and requirements
- Principle: grind a spherical cavity with a rotating ball and abrasive slurry, then examine crater geometry microscopically to find the coating–substrate interface.
- Mandatory conditions:
- Adequate optical contrast between coating and substrate (or use SEM/etching).
- Smooth, flat specimens (local radius of curvature criteria given in the standard).
- Clean specimen and ball preparation (e.g., ultrasonic cleaning).
- Test parameters (to be selected/recorded):
- Ball diameter, contact load, sliding speed, abrasive type and concentration, slurry feed rate, test duration.
- Example parameters: 25 mm ball, 0.25 N load, 100 r/min, 1 µm diamond in ethanol (1:4), 20 drops/min, 5 min (typical for 3–5 µm hard coatings).
- Measurements:
- Measure outer (D) and inner (d) crater diameters (or X and Y projections), using calibrated imaging.
- At least five measurements to assess repeatability.
- Calculations:
- Preferred formula for thickness: h = (D^2 − d^2) / (8 r), or simplified forms h = (X·Y)/(2 r) for small penetrations.
- Can be applied to multilayers by selecting appropriate crater circles.
- Uncertainty & errors:
- Main error sources: crater dimension uncertainty, deviations from circularity, mismatch between crater and ball radii.
- Standard includes annexes on error sources and uncertainty estimation.
- Reporting:
- Reports should follow ISO/IEC 17025 requirements and include test parameters, results, uncertainty, and micrographs with calibrated scale.
Applications and users
- Useful for quality control, process monitoring and R&D of coated ceramic components, cutting tools, wear-resistant parts, and functional thin films on ceramics.
- Typical users: ceramic manufacturers, coatings suppliers, materials testing laboratories, tribology labs, and tooling engineers seeking an accessible, reproducible method to measure coating thickness on advanced ceramics.
Related standards
- ISO 18452 - Step height method (alternative thickness measurement using profilometry)
- ISO 3290-1 - Specification for bearing balls (used as grinding balls)
- ISO/IEC 17025 - Laboratory competence and reporting requirements
Keywords: ISO 26423:2009, crater-grinding method, fine ceramics, coating thickness, advanced ceramics, measurement uncertainty, abrasive slurry, ball diameter, microscopic examination.
Open preview (PDF)Fine ceramics (advanced ceramics, advanced technical ceramics) — Determination of coating thickness by crater-grinding method