CVD Tungsten Carbide Coating Qualified by Airbus as an Environment-friendly Alternative to Hard Chrome Plating.

Since the September 2017 “sunset date”, EU REACH regulations restrict the use of toxic Cr6+ salts necessary to produce Hard Chrome plating (HCP), which is widely used to protect steel parts against wear, galling and corrosion. The US OSHA also tightened the Cr6+ exposure limits making HCP increasingly expensive and less available. The aerospace industry has been preparing for these regulatory changes over the last 15 years and has identified several HCP alternatives, but none of them had been able to replace HCP in all its applications.

Hardide Chemical Vapour Deposition (CVD) Tungsten Carbide coating was recently added to the aerospace-approved HCP alternatives when it was technically qualified by Airbus. In 2017 the Hardide UK production site passed the stringent Industrial Qualification process and gained Approved Supplier status from the Airbus Group for the coating of flying components. This coating fills some significant gaps among other HCP alternatives as it can be precision applied to both external and internal surfaces including complex geometries and thin walled parts, which are difficult to coat by other technologies.

Hardide-A type coating was specifically developed for aerospace applications, matching the HCP thickness (50…100 microns) and hardness (800…1200 Hv). This matching significantly simplifies the switch from HCP to Hardide-A as there is no need to change the pre-coating drawings and dimensions or perform stresses calculations and testing. The coating has enhanced resistance to wear, corrosion, galling, and shown excellent fatigue properties (minimum fatigue debit). This paper will present key technical properties of the CVD coating, compare its strength and weaknesses against other HCP alternatives and give examples of its applications.

In 2016, Hardide Coatings opened a coating facility in Virginia, USA, making this advanced coating readily available to aerospace engineers in North America who are working on the challenging task of Chromate-free aircraft design.