Context: Protecting Tungsten Weights
Black chromium is a specific plating applied to tungsten substrates (heavy metal cores) used as balancing weights. These weights are critical for stabilising helicopter rotors and reducing vibrations.
While the coating is non-decorative (matte black) and set up for anti-reflective applications, its primary function here is anti-corrosion. It is widely used in aeronautics, and for military applications.
The tungsten substrates on which it is applied are highly sensitive to oxidation and, more specifically, to galvanic corrosion, an electrochemical reaction that eats away at metal when two different metals are in contact in the presence of an electrolyte like moisture.
Therefore, these parts require robust surface protection to ensure their integrity over time. Due to its excellent anti-corrosion properties, adhesion, and friction performance, black chromium was the long-standing choice.
The Regulatory Challenge (REACh)
However, the traditional black chromium bath contains Hexavalent Chromium compounds (CrVI).
This substance is heavily impacted by the REACH regulation (the European Union’s strict regulation regarding the Registration, Evaluation, Authorisation and restriction of Chemicals). This is due to the compound’s classification as CMR:
- Carcinogenic (causes cancer),
- Mutagenic (causes genetic mutations),
- Reprotoxic (toxic to reproduction).
Because hexavalent chromium is subject to rigorous industrial oversight, adopting alternatives has become a strategic necessity. Based on technical research, a replacement coating—compliant with REACh and based on Chromium III (trivalent chromium), which is non-toxic—has been identified to protect these specific tungsten parts.
