It’s all about the coatings!

In a Q&A session, Toby Middlemiss, head of aerospace and surface technology specialist at Oerlikon assesses the trends and demands on the company in working within the challenging and ever-evolving aviation industry.

With a couple of highly strategic announcements made during the Paris Airshow, Oerlikon is consolidating its leadership in advancing metal additive manufacturing (AM) part production for aero and space applications.

Firstly, Oerlikon AM and Airbus have successfully industrialised the AM process for complex serial production of antenna clusters. These will be used in a series of communication satellites that will be orbiting earth soon. This marks an important milestone in the ten-year collaboration between both companies in an area requiring absolute accuracy and has resulted in a €3.8 million contract to additively manufacture these satellite components.

Secondly, Oerlikon AM and ArianeGroup signed an order worth up to €900,000 to produce 3D printed sets of heat exchangers for the new Ariane 6 rocket launcher. The successful cooperation with ArianeGroup and the use of additively manufactured components is another important milestone for Oerlikon on the way to consolidate its position as a recognised supplier of AM parts to space companies.

Finally, Oerlikon and MTU Aero Engines intend to collaborate on the further development of engine components, materials, and surface technologies for aircraft engines. The two companies signed a five-year agreement at the Paris Airshow to this effect. Both partners will contribute their technological know-how and industry expertise to further optimise efficiency and sustainability of engine components.

Q: Firstly, bring me up to speed with the latest coating developments taking place within Oerlikon.

Oerlikon had developed a new generation of high temperature coatings with improved corrosion resistance for use in high pressure turbines. These coatings have an excellent Calcium Magnesium Aluminium Silicate (CMAS) resistance, compared to the previous generation of high temperature coatings. The coatings are rigorously tested in our facilities in the US and Switzerland and by our aviation customers.

Q: What are the current heat treatment and surface technology challenges that face aero engine and landing gear OEM manufacturers?

Current challenges are multiple. Hard chromium, which has a lot of applications on landing gear parts and on engine accessories needs to be replaced with REACH compliant coatings. There are several alternatives: HVOF sprayed coatings or PVD (Physical Vapour Deposition) coatings. However, requalifying parts that previously had a hard chromium coating, takes a lot of effort.

Engine temperatures get higher and higher. Therefore new corrosion phenomena like CMAS occur, that cause heavy corrosion to the engine parts. New coating solutions need to be adapted to cope with this. Also, rising compressor temperatures require new types of coatings that are resistant to the higher temperatures and high temperature corrosion. And finally, increasing LPT temperatures also result in the need for new corrosion resistant coatings for LPT blades and LPT vanes. The classic aluminide coatings are no longer adequate if the LPT temperature goes beyond 850ËšC.

Q: And what are the demands placed on you in providing solutions that cater for any corrosion/erosion resistance, paint coating adherence, lightweighting, for example?

For Oerlikon Surface Solutions, corrosion and erosion resistance are key. We also see more need for designs with internal cooling features. This is because of increased engine temperatures. AM makes it possible to design and manufacture parts that have these internal cooling features build in during manufacturing.

Q: Tell me more about your thermal spray processes, plus any environmentally friendly aspects? What benefits do your thermal processes offer in terms of wear and corrosion resistance?

Oerlikon offers the full range of thermal spray processes and equipment: air plasma spray (APS), vacuum and low vacuum plasma spray (VPS, LVPS), high velocity oxygen fuel spray (HVOF), powder flame spray (PFS), wire flame spray (WPS) and dual arc wire spray. For these spray technologies, Oerlikon OSS delivers the full suite of materials. Next to that, Oerlikon offers a full spectrum of machines and services for physical vapor deposition (PVD) and chemical vapor deposition for thin coatings.

Oerlikon OSS develops and supplies advanced thermal barrier coatings with improved corrosion resistance for enhanced engine temperatures. Next to that, OSS is market leader in advanced abradable coatings for aero engines for both the low temperature as well as the high temperature section of the engine.

In the PVD area, OSS has developed wear resistant coatings, used on aero engine components and erosion resistant coatings for use on compressor air foils. The newest developments are erosion resistant coatings that can be applied to CFRP. This requires a low application temperature for which OSS has developed a technology. Oerlikon also launched two completely new materials for high-speed laser cladding applications.

Q: What kinds of rigorous testing procedures do your processed parts undergo to ensure they pass airworthiness regulations?

Parts are extensively tested during their design phase and during the design of the engine. Many of these parts have Oerlikon coatings. The coatings are therefore tested as part of the development and engine testing by the OEMs.

Oerlikon has extensive in-house testing for coatings. Our abradability test facility in Switzerland is world class leading and is used by all the major OEMs. Furthermore, we provide mechanical and thermal testing in our labs in Switzerland, Liechtenstein and the US. We offer over 40 different test capabilities.

Q: Is the aerospace industry a difficult one to do business in, bearing in mind all the flight safety related regulations, accreditations and certifications you need to satisfy?

Indeed, it is not easy to qualify as a supplier to the aerospace industry. On our AM roadmap to partner with the space industry, we have positioned ourselves as a reliable innovator producing increasingly sophisticated additive manufactured components. While antennas and heat exchangers are vital parts of a satellite, they are typically not mission critical. However, in the development of these key components, we were given the unique opportunity to gain further insight into modern-day satellite operations and to also demonstrate our capabilities to produce crucial components. On our journey to create flight-critical parts for the commercial and aerospace industries, we are now at an advanced stage of technical and operational maturity.

Q: What developments do you see happening in the construction and surface protection of aerospace components? Can composites ever replace safety critical aircraft parts or do existing metallic alloys offer more tried and trusted solutions?

The OEMs are continuously exploring possibilities to reduce the weight of components. Composite materials play a key role here. In certain areas of the engine, metallic components can be replaced with composite materials, provided that these composite materials have the right surface protection, e.g. for erosion resistance. This is where OSS coatings are a solution.

The same applies to AM. It is still a technology that must be further developed, but eventually it will replace certain components that are now made from forgings or castings. Everything in aerospace is about certification. Once it can be demonstrated that a technology or a material meets the certification requirements, than it can be allowed to be used on an aircraft. One must keep in mind that this are very lengthy processes that may take many years to complete.

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