Author

Sarah Higgins, Laboratory Manager at ATL Turbine Services

4 minute read

Chrome-Free Diffusion Coatings for Gas Turbines: Meeting the Challenge of REACH Legislation

The gas turbine sector is facing a significant regulatory shift. Under UK REACH legislation, hexavalent chromium (Cr⁶⁺) is being removed from industrial coatings due to its classification as a carcinogen, not diffused, not converted, just phased out. A twelve-year extension has been granted, but in the world of coatings, that is more of a countdown than a comfort. The coatings we’ve relied on for decades are being retired, and the challenge isn’t just finding something that looks good in a lab, it’s finding a coating that can take the heat, shrug off the sulphur, and still show up to work after months of punishing service conditions.

ATL Turbine Services recognised early that this wasn’t just a compliance issue, it was a technical challenge that demanded a proactive, research-led response. As part of this effort, Laboratory Manager Sarah Higgins, who is currently undertaking a PhD in Metallurgical and Mechanical Engineering, led a detailed validation programme to assess chromium-free alternatives, combining academic research with industrial application.

Cr⁶⁺-based coatings like IP1041 have been widely used for over three decades, offering reliable protection against oxidation, sulphidation, and hot corrosion at high temperatures. Their performance is well understood, and they are deeply embedded in repair and maintenance practices across industrial, marine, and aero gas turbines. Replacing them is not a simple task.

The challenge lies in identifying alternatives that match the metallurgical behaviour, durability, and corrosion resistance of legacy coatings, while also complying with evolving health and environmental standards. Many proposed substitutes fall short in one or more areas, particularly when exposed to aggressive thermal environments or extended service conditions.

In response to this, Indestructible Paint Ltd has developed CFIPAL, a chromium-free aluminium slurry coating designed to replicate the performance of IP1041. CFIPAL maintains the same diffused aluminide structure and is compatible with existing superalloy substrates, allowing for a familiar application process.

CFIPAL’s suitability as a drop-in replacement was assessed through a comprehensive testing programme led by Sarah Higgins and supported by ATL Turbine Services. Metallurgical analysis was performed using scanning electron microscopy, electron backscatter diffraction, and optical microscopy. Mechanical and surface properties were assessed through hardness, roughness, and contact angle measurements. Corrosion resistance was evaluated through both salt spray and hot corrosion testing.

The results showed that CFIPAL forms a uniform, well-adhered aluminide layer with comparable grain morphology and diffusion characteristics. Mechanical testing confirmed similar hardness and surface roughness, and corrosion trials demonstrated that CFIPAL not only matched but outperformed IP1041. After 1488 hours of salt spray testing, CFIPAL-coated samples maintained structural integrity with no significant degradation, and the diffusion zones remained intact. Hot corrosion trials also showed CFIPAL’s resilience in aggressive thermal environments, reinforcing its potential as a robust and future-ready solution for gas turbine applications.

The development and validation of CFIPAL offer a practical path forward for the gas turbine repair sector. It enables operators to maintain coating performance while improving safety and regulatory resilience.

ATL Turbine Services, recognised as a leading applicator of CFIPAL, is supporting this transition with its expertise in coating application and process control. Their involvement ensures that the move to chromium-free solutions is both technically robust and operationally smooth.

As the industry moves forward, collaboration between suppliers, applicators, and operators will be essential. CFIPAL proves that it’s possible to meet demanding performance standards without relying on legacy materials. It’s a coating that’s ready now, not something we’ll revisit in eleven years and eleven months. And if nothing else, it’s reassuring to know that the solution doesn’t come with a carcinogen warning label.