Overview
ISO 22778:2006 - "Metallic coatings - Physical vapour‑deposited coatings of cadmium on iron and steel - Specification and test methods" - defines requirements and test methods for high‑purity cadmium coatings applied by physical vapour deposition (PVD) to iron, steel and other substrates. The standard covers coating composition, minimum thicknesses, designation conventions (including chromate conversion and supplementary treatments), sampling, rejection criteria and specified test methods to verify compliance. It also notes service limitations (not suitable where parts reach ≥225 °C) and highlights health/environment considerations for cadmium use.
Key topics and technical requirements
- Scope and materials: High‑purity cadmium coatings produced by physical vapour deposition for iron, steel and other substrates. Emphasises vacuum PVD benefits (minimal hydrogen uptake vs electroplating).
- Coating thickness: Minimum local thicknesses are specified (examples): steels - typical 15 µm; small threaded articles and bores - lower minima (e.g., Cd4 to Cd8 depending on diameter). Designation uses “Cd” plus micrometres (e.g., Cd5, Cd8).
- Designation system: Full designation includes “vapour‑deposited coating ISO 22778 – [basis metal]/[pre‑treatment]/CdX/[chromate]/[supplementary treatment]”. Pre‑ and post‑heat treatments are indicated (e.g., [SR(150)2], [ER(400)12]).
- Chromate & supplementary treatments: Chromate types and coatings are coded (A = clear, C = iridescent yellow, D = opaque olive‑green, F = black) with mass per unit area ranges; supplementary treatments (T1–T5) include paints, sealants, dyes, greases, wax. Chromium‑free alternatives are acceptable if corrosion performance is met.
- Hydrogen embrittlement control: Addresses stress‑relief and post‑coating heat treatments and references pre/post‑treatment standards to reduce hydrogen embrittlement risk.
- Test & inspection methods: Specifies sampling, measurement of thickness and adhesion (normative annexes) and references measurement/test standards (XRF, coulometric, microscopy, salt spray, etc.).
- Safety and limits: Warns about cadmium toxicity and service temperature limits (225 °C).
Practical applications
- Aerospace, defence, and critical mechanical components where cadmium’s corrosion resistance, ductility, electrical conductivity and low contact resistance are essential.
- Fasteners, threaded assemblies, small bores and high‑strength steels where hydrogen embrittlement risk is a concern and where vacuum PVD is preferred over electroplating.
- Situations requiring specified chromate conversion finishes or subsequent paint/sealant systems.
Who should use this standard
- Coating processors and PVD service providers, OEMs and procurement engineers specifying protective coatings, quality/inspection teams verifying coatings, and design engineers working with high‑strength steels or critical assemblies.
Related standards (selected)
Keywords: ISO 22778, cadmium coatings, physical vapour deposition, PVD cadmium, coating thickness, chromate conversion, hydrogen embrittlement, test methods, coating designation.