ISO 19674:2025

Overview

ISO 19674:2025 specifies a test method for determining the internal (residual) stress in thin ceramic coatings by applying the Stoney formula to measured changes in the radius of curvature of isotropic strip or disc specimens with a single-face coating. The method is intended for fine (advanced) ceramics and requires well-characterized substrates, accurate measurement of coating and substrate thicknesses, and careful profile measurement before and after coating.

Key SEO phrases: ISO 19674:2025, fine ceramics, ceramic coatings, internal stress, Stoney formula, residual stress measurement, radius of curvature.

Key technical topics and requirements

• Principle: Internal stress is calculated from the coating-induced bending of a substrate using the Stoney formula. The technique assumes elastic deformation, spherical curvature and thin-film conditions.
• Specimen constraints:
  • Only isotropic substrates (scope limitation).
  • Strip specimens preferred; discs are acceptable.
  • Substrate must have uniform thickness and be stress-free prior to coating (anneal if necessary).
  • Coating thickness should be small compared with substrate thickness (document notes < 2 % as a guideline).
• Material properties needed: Young’s modulus and Poisson’s ratio of the substrate (the coating’s elastic constants are not required for the Stoney approach).
• Measurement/ Apparatus:
  • Profile measurement options include optical profilometers, high‑magnification optical microscopes (~1 µm resolution), laser systems (~5 µm), micrometer stages; Newton’s rings or optical bench methods for polished discs.
  • Careful calibration and low-contact forces (if using a contact profilometer) are required to avoid altering the sample profile.
• Procedure highlights:
  • Measure initial profile, deposit coating, measure coating thickness and final profile, then calculate mean film stress from measured radius of curvature.
  • The method includes guidance on specimen geometry selection, number of repeat measurements, and limits to avoid plastic deformation (consider temperature-dependent yield behavior).
• Limitations: Produces the mean stress through film thickness; results reflect intrinsic growth stress plus thermal mismatch effects if deposition occurs at elevated temperature.

Practical applications and users

• Who uses it: materials scientists, coating process engineers, R&D and QA laboratories in ceramic and advanced materials industries, and manufacturers of thermal barrier, wear-resistant or functional ceramic coatings.
• Practical uses:
  • Quantifying residual stress for process development and optimization.
  • Comparing coating processes or materials for lifetime and adhesion modelling.
  • Supplying input parameters for stress/thermal-mechanical modelling of coated components.

Related standards

• ISO 18452 (step height measurement) - referenced for coating thickness methods
• ISO 26423 (crater grinding) - referenced for thickness determination
• EN 1071-10 (cross-sectioning) - referenced for thickness determination

ISO 19674:2025 provides a practical, standardized approach to thin-film stress measurement in ceramic coatings using curvature data and the Stoney formulation, helping link laboratory measurements with component performance and modelling.