Overview
ISO 23458:2020 specifies a test method for determining the linear thermal expansion coefficient (up to 2 300 K) and the residual stress (evaluated at room temperature) of chemical vapour deposition (CVD) ceramic coatings thicker than 0.03 mm. The standard covers specimen preparation, test modes, heating/cooling rates, apparatus and measurement accuracy, data collection, calculation procedures and reporting requirements. It applies to CVD ceramic coatings on metal or ceramic substrates and is intended for material research, quality control, characterization and design data generation.
Key topics and technical requirements
- Measurement principle: a relative method comparing a coated composite bar and an uncoated substrate bar to deduce the coating expansion coefficient and residual stress via geometric compatibility and elastic equilibrium models.
- Temperature range: thermal expansion coefficient determined up to 2 300 K; residual stress reported at room temperature.
- Specimens: symmetric coating configurations allowed (two-face, four-face, around/cylindrical). Recommended specimen sizes: length 30–50 mm, cross-section ~5 mm, coating thickness > 0.03 mm, and thickness ratio h/H (or h/D) < 1/4. A minimum of three pairs of test pieces is required for comparison.
- Apparatus & sensors:
- Furnace capable of controlled atmosphere and temperature control within 1% of mean temperature.
- Thermocouples per IEC 60584-1; for >2 000 K, infrared detectors or suitable devices may be used.
- Displacement measurement accuracy better than 0.0001 mm; recording error ≤ 1%. Minimum data collection frequency 15 Hz (50 Hz recommended response).
- Dimensional measuring tools: vernier (ISO 3611) with precision 0.02 mm or better; coating thickness via optical microscope at ×1 000 or better.
- Calculations: thermal expansion coefficient (α) from measured length changes and known substrate properties (ISO 17139 referenced); residual stress (σ) computed from α, elastic moduli, coating-to-substrate area ratio and coating temperature history (elastic modulus measurement referenced to ISO 19603).
- Reporting: procedures for documenting specimen geometry, measurement conditions, apparatus, data, calculations and uncertainties.
Applications and users
ISO 23458:2020 is used by:
- Materials scientists and ceramic engineers studying CVD ceramic thermal behavior
- Coating manufacturers and process engineers for quality control and process validation
- Test laboratories performing characterization and certification of advanced ceramic coatings
- Product designers and simulation teams needing accurate thermal and stress input data for components with CVD coatings
Keywords: ISO 23458:2020, CVD ceramic coatings, thermal expansion coefficient, residual stress, test method, fine ceramics, advanced ceramics, characterization, quality control.
Related standards
- ISO 17139 - thermophysical properties / thermal expansion testing
- ISO 19603 - elastic modulus and bending strength of thick coatings
- ISO 3611 - dimensional measuring equipment (micrometers)
- IEC 60584-1 - thermocouples (EMF specs and tolerances)
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