Getting into gear with coatings


Whether you are promoting the coating or innovating with plating, advanced surface coating company, Hardide Coatings’ vice-president of global aerospace, Stewart Gibson has all the answers. Aerospace Manufacturing reports.

Hardide Coatings develops, manufactures and applies advanced technology tungsten/tungsten carbide metal matrix coatings for a wide range of high wear/high value components. Its patented technology combines, in one material, a mix of toughness and resistance to abrasion, erosion and corrosion; together with the ability to coat accurately interior surfaces and complex geometries.

The company’s Hardide-A coating has been developed specifically to meet the needs of the aerospace industry and is an environmentally compliant and technically superior replacement for high velocity oxy-fuel (HVOF) and hard chrome plating. In April 2020, the company was awarded the Queen’s Award for Enterprise: International Trade.

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

One of the challenges facing OEM manufacturers is extending seal life. This requires a combination of surface finish characteristics in a coating that does not damage the seal and cause oil leakage. Corrosion of the actuator piston is another challenge, especially for aircraft used in hot and humid climates where the humidity and inspect sprays used can affect the cobalt binder in WC/Co HVOF coating. A corroded piston can lead to accelerated seal wear and oil leakage. Historically, many landing gear components have used hard chrome (Cr) plating to protect against corrosion and galling.

Since 2017, the EU REACH regulations have restricted the use of toxic hexavalent Cr salts, making hard Cr plating less available and more expensive. For the last 15 years, finding a replacement for hard Cr has been a major challenge for the landing gear OEMs. This search is continuing, especially for complex shaped parts and internal surfaces where HVOF is difficult to apply.

Hardide’s coating reactor being loaded with parts

Hardide advanced tungsten carbide/tungsten metal matrix composite coatings are proven to provide a better performing alternative to hard Cr and can be applied on parts difficult or impossible to coat by HVOF and other traditional methods.

Q) And what are the demands in terms of providing solutions that cater for any FOD prevention, corrosion resistance, paint coating adherence, etc.?

The OEMs have a holistic approach to lower lifecycle costs for landing gear by developing and improving material selection and surface enhancements. Hardide Coatings has been focused on the need to improve actuator shaft seal life and reduce oil leakage by improving surface characteristics, lowering friction and increasing abrasion and impact resistance. Due to its performance, Hardide’s low temperature chemical vapour deposition (CVD) coatings are now being considered for other components within the landing gear set.

The Hardide-A metal matrix composite tungsten carbide/tungsten nano-structured CVD surface coating is a direct replacement for hard Cr and HVOF. It matches the thickness and hardness of hard Cr and outperforms both coatings in several critical areas providing enhanced protection against galling, corrosion, wear, fretting and fatigue. It is also suitable for a wide range of metallic substrates.

Q) Tell me more about your surface coating processes and any environmentally-friendly aspects?

The Hardide-A coating has been developed specifically to meet the needs of the aerospace industry and is an environmentally compliant and technically superior replacement for HVOF and hard chrome plating. Hardide coatings are also seal-friendly and due to their structure, they maintain the required surface finish, even in highly abrasive and corrosive environments, thus preventing premature seal wear.

facility in Bicester

Hardide Coatings has attained Nadcap certification for the process which is also fully REACH compliant. The company also holds AS9100 and ISO 14001 approval. The use of Hardide coatings removes chrome from the coating product and can also be an alternative to the use of other harmful materials, such as cadmium. The low temperature, CVD process allows a homogeneous and conformal coating to crystallise through the flow path of components. By eliminating through porosity or leak paths for gases or liquids through the coating layer, this results in excellent corrosion protection which prolongs the life of critical components and reduces maintenance and downtime. This lowers costs and improves overall operational efficiency, thus reducing environmental pollution.

Q) What components are your solutions most suited to?

Where there is friction, abrasion, severe wear and corrosion as well as impact and high loads, the Hardide coating can provide a solution for intricate geometries, internal bores and straight outside diameters. Where maintaining a low fatigue debit is a requirement, the Hardide coating is proven to have a negligible effect on fatigue life. The coating is suitable for high wear, high value applications operating in extreme environments, especially applicable where other coatings have failed.

Some examples of applications include: actuators, bearing systems, control system components, metering valves, door systems, flap support, compressor blades and vanes, high lift systems – flaps, slats and spoilers, hydraulic and pneumatic cylinders, landing gear retract mechanisms, steering components, thrust reverser and flap torque shafts, torque tubes and pins, wheel axels and pins and wing structure components.

Q) What aircraft programmes are you working on and how do you engage and coordinate them?

The Hardide coating is approved for flying components on the BAE Systems Eurofighter Typhoon. This was to resolve a galling problem on canopy bushes which caused severe vibration and even seizure of the canopy operation. The Hardide coating was tested and approved within six months. We are also approved by Airbus for the replacement of hard Cr covering various wing components for A380, A400M and A330 aircraft. Following extensive testing, the Hardide-A coating has been approved for use on drag chute components for the Lockheed Martin F-35A CTOL variant. For these specific components, Hardide-A is being used in place of HVOF thermal spray coatings. For Leonardo Helicopters, we are developing a number of advanced coating solutions for gear shaft and blade components designed to significantly reduce process costs and extend wear life. Hardide Coatings’ R&D and business development teams co-ordinate projects with major OEMs and MRO companies, usually covering several years of development.

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

Our Hardide-A coating has undergone several years of testing by the major aerospace OEMs including Airbus, Leonardo Helicopters, BAE Systems and Triumph Group. This includes wear, abrasion to ASTM G65, fatigue testing, impact rig testing, salt corrosion testing and bond strength tests. Procedurally, we comply with Nadcap and AS9100 rev D. This includes witness sampling for the components we process which are subject to full metallurgical analysis in our extensively equipped laboratories including SEM analysis.

Stewart Gibson - VP of global aerospace

Q) What developments do you see happening in the construction and surface protection of landing gear systems?

Landing gear supports the entire weight of the aircraft, so it has to be incredibly sturdy. OEMs are developing new materials, some being composite design, in order to reduce weight and noise. Steel configurations are also being further developed due to their surface hardness, stiffness, resistance to fretting and fatigue. Critical steel parts are regularly inspected using well-developed non-destructive inspection techniques. This is one of the challenges for composites where subsurface defects could be extremely difficult to detect and may lead to a catastrophic failure of a critical part. Coating of composites is a focus for future development in combination with coated steel infrastructure.

Q) With so many aircraft sitting around during the pandemic, has there been an increase in business in terms of aircraft becoming airworthy again?

Hardide coatings can help make aircraft components more durable and reduce maintenance requirements, thus reducing operational costs. The Hardide coating process is at an early stage of deployment across the aerospace industry. The opportunities in the MRO/aftermarket sector continue to grow as aircraft are brought back into service and require maintenance. The market for Hardide coatings for both new build and MRO has been well established with several key applications enabling further penetration and sales growth. As the world moves to more eco-friendly alternatives and higher performing surface treatments, Hardide Coatings is well positioned to service the global opportunities with extensive modern manufacturing capabilities in Bicester, UK and Martinsville, Virginia, USA. This ensures fast response times to support the global aerospace market and provide a secure dual source.

Q) Please provide the latest developments on your factory upgrade?

Hardide Coatings has recently relocated to a new 20,000ft2 facility in Bicester, Oxfordshire, which has double the floor area of the old site. This has enabled us to develop a world-class coating and technical facility, ‘state-of-the-art’ laboratory and to install additional coating capacity including a new, large reactor capable of taking components up to 1,500mm long.

Q) Where to next for your company in aerospace?

Central to our company vision, Hardide Coatings aims to be at the forefront of technology, helping customers to innovate as we develop joint technology collaborations and ensure a commitment to the continued development of our greener coatings and operations. Hardide coatings are fast becoming the next generation of green technologies for the aerospace industry and the company continues to focus on applications with major OEMs in the civilian, defence and space market sectors.

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