Overview
ISO 22680:2020 specifies a standardized method to measure the linear thermal expansion coefficient of ceramic top coats (TCs) used in thermal barrier coatings (TBCs) - up to 1 300 °C. It addresses reproducible measurement of TC dilatation behavior (not the metallic bond coat or substrate) and fills a gap left by standards that target monolithic ceramics. The procedure covers specimen preparation, apparatus requirements, measurement cycles and reporting essentials.
Key topics and technical requirements
- Scope and principle
- Measures mean linear thermal expansion coefficient α(T) of ceramic top coats of TBCs.
- Requires repeated heating cycles because TCs commonly show unstable expansion during initial cycles; testing continues until a reproducible value is reached.
- Specimen preparation
- TC is separated from the TBC (chemical stripping or mechanical machining) into a free-standing plate.
- Minimum specimen size: length ≥ 10 mm, width ≥ 5 mm, thickness ≥ 0.5 mm; thickness chosen to avoid warping.
- Apparatus and setup
- Typical components: furnace, push rod, load control, differential transformer, recorder and thermocouple (tip close to specimen per ISO 17562).
- Supporting jig must allow free dilatation, prevent tilting, be chemically compatible with specimen; high-purity alumina recommended.
- Calibration required using a reference specimen per ISO 17139.
- Measurement procedure
- Heating rate: 1 °C/min to 5 °C/min.
- Push-rod contact force: 0.1 N to 1 N.
- Temperature increment for computing α(T): approximately 50 °C.
- Repetition continues until the criterion Z(T) ≤ 5% is met - i.e., the relative difference between successive measurements is within 5%.
- Reporting
- Must include specimen details, apparatus and materials, force/heating/atmosphere, number of measurements, expansion curve and α(T) values, and any deviations.
Applications and users
ISO 22680:2020 is relevant to:
- Coating manufacturers (plasma-sprayed, EB-PVD, etc.) validating TC thermomechanical properties.
- Turbine OEMs and aero/industrial gas-turbine component designers evaluating TBC performance.
- Materials and thermal-mechanical testing laboratories performing quality control and R&D.
- Researchers studying high-temperature behavior of ceramic coatings for engine and power-generation applications.
Keywords: ISO 22680:2020, thermal barrier coatings, linear thermal expansion coefficient, TBC, ceramic top coat, thermal expansion measurement, high-temperature testing.
Related standards
- ISO 17139 - thermophysical properties of ceramic composites (reference specimen & apparatus calibration)
- ISO 17562 - push-rod technique for monolithic ceramics (thermocouple placement guidance)
- ISO 14188 - TBC thermal cycle and shock test methods
This standard ensures consistent, reproducible measurement of TC thermal expansion, supporting reliable material selection, coating development and component life prediction at elevated temperatures.