With global passenger air travel on the increase, aircraft manufacturers are struggling to handle the pressing demand. The close of 2017 saw a record-breaking backlog of more than 14,000 units, while the industry as a whole is anticipating revenue growth of 4.8%. For plating suppliers, this news is welcome: aircraft use vast volumes of plated components for manufacture as well as for replacement parts.
As with lots of other resource-heavy industries, there is mounting pressure on the aerospace sector to adopt more environmentally friendly measures and practice. In response, the aerospace industry are working to limit the use and production of hazardous materials and cut emissions.
A main focus for airlines is to cut emissions through increased fuel efficiency, as they are a major contributor to greenhouse gases. This fuel efficiency can be attained in two ways: either by reducing the weight of the aircraft or by increasing the engine efficiency itself. Both approaches influence the materials used within construction of the aircraft, which includes the plated components.
Increasing Aircraft Efficiency
It can seem ridiculous to suggest that thinner platings make a difference when comparing the weight of the plating on a single component with the weight of an entire aircraft. In fact, there are so many plated components involved in aircraft production that trimming fractions of microns off each component’s plating thickness does add up. Without reducing the part’s lifetime, the thinner the coating, the better.
Everything depends on heat regarding engine efficiency. The greater temperature at which the engine can run, the more mileage can be generated from each gallon of fuel. For aircraft engineers, the restricting factor is how much heat the engine can take before the failure of the components. For plated parts, this translates into how much heat the component can handle before the underlying metal starts to corrode and the plating fails.
Minimizing Hazardous Waste
Historically, cadmium plating has propped up in the aerospace industry for its ability to reduce corrosion. However, the high toxicity of cadmium means that today it is subject to strict environmental controls. The EU has strict regulations on cadmium and has placed it on the list of substances of very high concern for REACH guidelines. It is vital to carry out new research into other plating materials, which can withstand high temperatures and prevent corrosion to replace cadmium.
Zn-Ni Replacing Cadmium as a Viable Plating Material
In aircraft applications, Zinc-Nickel (Zn-Ni) has displayed exceptional performance and is rapidly becoming a viable alternative to cadmium. Zn-Ni creates a thin, consistent layer across the surface to be coated at the crystal structure level, meaning that complex or uneven surfaces can be plated easily with a high quality and even finish.
This naturally thin and smooth finish improves the part’s wear resistance, which is especially significant for moving parts - particularly in aircraft, where failure can be catastrophic.
One of the key advantages of Zn-Ni is its ability to reduce the effect of thermal stress on components. As this article has previously explored, the ability of components to run safely at higher temperatures assists with the goal of fuel efficiency. Tests have proven that Zn-Ni-coated parts resist corrosion for temperatures of up to 200 °C.
Using XRF to Measure Zn-Ni Thickness in a Production Environment
Zn-Ni must be exactly the right thickness and composition within an aircraft application to protect the underlying substrate but still keep the weight down. For individual layers, deposited zinc-nickel thicknesses are within the micron and sub-micron level.
X-ray fluorescence (XRF) analysis is a fast, accurate and non-destructive way to measure the thickness and composition of these layers. To obtain the most accurate readings, users will need to use XRF equipment in conjunction with the right kind of detector. Nickel and zinc are very close to one another on the X-ray results spectrum, which means that some XRF analyzers may find it difficult to distinguish between the two. Equipment that has a silicon drift detector (SDD) helps to obtain a better resolution, which makes for improved accuracy.
This information has been sourced, reviewed and adapted from materials provided by Hitachi High-Tech Analytical Science.
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