Global passenger air travel is on the increase and aircraft manufacturers are struggling to keep up with demand. At the end of 2017, there was a record backlog of over 14,000 units, and the industry as a whole is expected to see revenues grow by 4.8%. This is great news for plating suppliers; aircraft use vast numbers of plated components – both for manufacture and for replacement parts.
But, like many other resource-heavy industries, the aerospace sector is under huge pressure to make changes to be more environmentally friendly. This means they are working to cut emissions and limit the use and production of hazardous materials.
As a major contributor to greenhouse gases, the main focus for airlines it to cut emissions through increased fuel efficiency. This can be done in two ways: reducing the weight of the aircraft and increasing the efficiency of the engine itself. Both of these approaches impact the materials used on the aircraft, including plated components.
When comparing the weight of the plating on a single component with the weight of an entire aircraft it can seem ridiculous to suggest that thinner platings make a difference. But there are so many plated components that shaving fractions of microns off the plating thickness of each component does add up. As long as it doesn’t reduce the lifetime of the part, the thinner the coating the better.
In terms of engine efficiency, it all comes down to heat. The hotter the engine is allowed to run, the more mileage you get from each gallon of fuel. The limiting factor for aircraft engineers is how much heat the engine can take before the components begin to fail. For plated parts, this means how much heat the component can take before the plating fails and underlying metal starts to corrode.
Historically, the aerospace industry has relied heavily on cadmium plating to reduce corrosion. But cadmium is highly toxic and is today subject to strict environmental controls. For example, in the EU, cadmium compounds are on the list of substances of very high concern for REACH regulations . This means that other plating materials that can withstand high temperatures and prevent corrosion are needed to replace the widespread use of cadmium.
Zinc-Nickel has shown excellent performance in aircraft applications and is fast becoming a real alternative to cadmium. At the crystal structure level, Zn-Ni creates a thin, consistent layer across the surface being coated. This means that complex or uneven surfaces can be easily plated with a high quality, even finish. This naturally smooth and thin finish increases wear resistance of the part, which is important for moving parts – especially in aircraft where failure can be catastrophic.
Perhaps one of the most beneficial features of Zn-Ni is that it reduces the effect of thermal stress on components. As discussed above, the ability of components to run safely at higher temperatures helps with fuel efficiency. Tests have shown that Zn-Ni coated parts provide corrosion resistance at temperatures up to 200°C .
Within an aircraft application, the Zn-Ni layer has to be exactly the right thickness and composition to protect the underlying substrate yet keep the overall weight down. Deposited zinc-nickel thicknesses are within the micron and sub-micron level for individual layers. X-ray fluorescence (XRF) analysis is the best way to measure the thickness and composition of these layers, as it’s fast, accurate and non-destructive. For the most accurate readings, you’ll need to use XRF equipment with the right kind of detector. On the X-ray results spectrum, nickel and zinc are very close to each other. This means that some XRF analysers might struggle to differentiate between the two peaks. Better resolution is achieved with equipment that has a silicon drift detector (SDD), allowing for improved accuracy.
If you are interested in learning more about using our XRF analysers to help with measuring very thin coatings, please get in touch. You can find out more information on the capabilities of our analysers here.