Overview
ISO 20267:2017 defines an indentation-based method to measure the interfacial toughness of thermal-sprayed ceramic coatings at room temperature. Using a Vickers hardness tester, the standard calculates a toughness value from the mean length of cracks that emanate from the corners of an indentation placed at the coating–substrate interface. The method is suitable for single-layer and multilayer ceramic coatings and is intended for ambient-environment testing of thermal barrier, wear‑resistant and electrical‑insulating coatings.
Key topics and technical requirements
- Test principle: Place a Vickers diamond indenter at the coating–substrate interface; measure crack lengths from the impression corners to determine the indentation interfacial toughness (K) and/or convert to energy release rate (G).
- Units and results: Results can be reported as a stress intensity factor (K, typically in MN·m−3/2) or as fracture surface energy (G, in J·m−2).
- Apparatus:
- Standard Vickers indenter and hardness tester complying with ISO 6507-1 / ISO 6507-2.
- Optical microscope with resolution ≈10 μm (recommended magnification ≥200×) to measure diagonals and crack lengths.
- Sample preparation:
- Substrate (including bond coat) recommended thickness: ≥ 5 mm.
- Coating thickness: at least 3× the half‑length of the impression (5× recommended).
- Sample width ≥ 5 mm (recommendations note wider samples reduce edge/stress effects); length > 20 mm.
- Embed specimens in resin, grind back ~0.25 mm to remove damage, and polish to a mirror finish.
- Test procedure:
- Indent with diagonal parallel to the interface; hold load for 10–15 s.
- Maintain spacing between indent centers ≥ 5× crack length (recommended ≥ 5 mm) and from edges ≥ 5 mm.
- Two accepted crack‑measurement methods are provided; define crack length as distance from impression center to crack tip or pore edge.
- Validity and reporting: The standard defines analysis steps, validity checks, and required report items to minimize uncertainty.
Applications and users
ISO 20267:2017 is used to evaluate adhesion and interfacial durability for:
- Aerospace, power‑generation and industrial turbine thermal barrier coatings (TBCs)
- Wear-resistant and electrical-insulating thermal-spray ceramics
- Quality control and acceptance testing in coating manufacturers
- R&D and failure analysis in materials laboratories and universities
- Coating selection and lifecycle assessment for engineered components
Related standards
- ISO 6507-1, ISO 6507-2 (Vickers hardness test and machine calibration)
- ISO 14916 (tensile adhesion testing; complementary method for adhesion assessment)
Keywords: ISO 20267:2017, interfacial toughness testing, thermal spray ceramic coatings, Vickers indentation, thermal barrier coatings, materials testing standard.