ISO 26423:2009

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.