Overview
ISO 21874:2019 - PVD multi-layer hard coatings - Composition, structure and properties - defines standardized methods to evaluate the composition, microstructure, surface quality, thickness and mechanical/tribological properties of multi-layer hard coatings produced by physical vapor deposition (PVD). It is intended primarily for coating development and laboratory evaluation of PVD multi-layer systems (e.g., transition metal nitrides and carbides), rather than routine production QA.
Key topics and requirements
- Scope & sample preparation
- Applies to PVD (evaporation, sputtering, arc, etc.) deposited multi-layer hard coatings.
- Samples should be polished to mirror finish (roughness Rpk < 0.05 μm) and ultrasonically cleaned before coating and testing.
- Chemical composition analysis
- Recommended techniques: EDS, EPMA, XPS, AES, SIMS, XRF, GDOES. Choice depends on element (B, C, N, O, metals), depth (surface vs cross-section) and destructiveness.
- Layer structure and microstructure
- Use SEM, TEM, SIMS to characterise columnar, equiaxed or amorphous structures, multi-layer stacks, nano-layered (modulation period Λ) and superlattice coatings. Annex A provides TEM specimen guidance.
- Surface quality / deficiency rate
- Quantify droplets, pinholes and shallow craters by SEM image analysis. Deficiency rate = (defect area / observed area). Polished coatings with ≤10% deficiency are acceptable; production-level tests recommend lower limits (example: <3% for nano-indentation-ready surfaces).
- Thickness measurement
- Use ball crater-grinding (ISO 26423) for thickness; SEM/TEM cross-section preferred for precise layer-by-layer measurements. ISO 9220 referenced for SEM specimen prep on metallic substrates.
- Mechanical and tribological properties
- Hardness: nano-indentation (ISO 14577-1) to avoid substrate influence (typical indentation depths ~50–200 nm); microhardness (Vickers ISO 6507-1, Knoop ISO 4545-1) requires indentation depth < 1/10 of coating thickness (Knoop better for >2 μm; Vickers for >4 μm).
- Friction & wear: ball-on-disc style tribology testing referenced (ISO 20808).
Applications and users
- Coating developers and R&D labs validating new PVD multi-layer recipes
- Materials scientists and TEM/SEM analysts characterizing microstructure
- Tribology and wear test laboratories assessing friction/wear performance
- Tool and component manufacturers (cutting tools, forming dies, wear parts) seeking performance benchmarking
- Quality engineers adopting standard evaluation methods during process transfer and qualification
Related standards
Keywords: ISO 21874:2019, PVD multi-layer hard coatings, physical vapor deposition, composition structure properties, nano-indentation, microhardness, SEM, TEM, SIMS, EDS, GDOES, surface deficiency rate, thickness measurement.
