An understanding of landing

2 Bodycote Derby's latest TAV vacuum furnace
2 Bodycote Derby's latest TAV vacuum furnace

Surface engineering specialist, Bodycote is continually broadening the capabilities of its coating solutions and ancillary services for landing gear to maximise its support for a supply chain under pressure. Aerospace Manufacturing reports.

Bodycote is among the leading suppliers of environmentally-friendly thermal spray coatings that are used extensively to improve the wear and corrosion characteristics of landing gear components. The company is currently involved in the Boeing 787, 777, Airbus A320, A350 and A380 aircraft programmes. Over time, Bodycote has implemented an investment strategy to specifically support the rapid growth of the landing gear supply chain.

In terms of the current heat treatment and surface technology challenges that face landing gear OEM manufacturers, Bodycote says there are growing efforts by a number of countries to try and eliminate the process of chrome plating undercarriage components, which has been determined to cause environmental and health hazards.

Manufacturers have now switched to High Velocity Oxy-Fuel (HVOF). In addition to being non-hazardous and environmentally-friendly, HVOF can apply surface coatings with greater integrity (chrome-plating can leak) and with improved surface finishes. The coating can also be used on actuators, helicopter rotor components and aero engine components.

Handle with care

The heat treatment of these components is a complex operation requiring precise control of time, temperature, and carbon control. Arguably, landing gear has perhaps the most stringent requirements for performance. They must perform under severe loading conditions and in many different environments. They have complex shapes and thick sections. Alloys used in these applications must have high strengths between 260 to 300ksi (1,792 to 2,068MPa) and excellent fracture toughness (up to 100ksi in.1/2, or 110MPa×m0.5).

The alloys used for landing gear have remained relatively constant over several decades. Alloys like 300M and HP9-4-30 are utilised. To achieve design and performance goals, heat treatments have been developed to extract the optimum performance for these alloys.

Vacuum processing followed by a gas pressure quench or oil quench offers various environmental and economic benefits over traditional hardening in controlled atmosphere furnaces, which is the existing route for heat treatment of landing gear parts. Processing in a vacuum allows you to control the surface chemistry and the decarburisation and high-temperature oxidation problems often associated with traditional controlled-atmosphere processing can be minimised. This process also allows manufacturers of landing gear to finish machine critical surfaces on components prior to heat treatment. As a result, OEMs and their first tier suppliers have adopted vacuum processing of landing gear components.

Well within reach

One key environmental issue facing the industry of course is REACH legislation. As part of these new regulations, the use of hexavalent chrome will be phased out and must be replaced with an alternative, less harmful material which meets the legislation criteria.

A direct alternative for chrome is thermally sprayed HVOF tungsten carbide, which has many benefits over chrome for wear and corrosion resistance, as well as being an environmentally friendly process.

Some key benefits of thermal spray over chrome include:

  • Less environmental impact with no major ecological and health & safety concerns

  • WC/Cr/Co coating has abrasion wear resistance 4-5 times higher than hard chrome

  • Coatings have negligible impact on substrate fatigue performance, whilst hard chrome plating can reduce substrate fatigue performance by up to 50%

  • Extended seal life on hydraulic components

  • Requires less masking than hard chrome plating and offers improved deposition quality adjacent to holes and keyways

  • Hard chrome plated high strength steels require heat treatment to prevent hydrogen embrittlement; this is not required with HVOF coatings

  • Coating of a wide range of materials with coating material tailored to the application, e.g. WC/Co/Cr, WC/Co, Cr3C2/Ni/Cr, WC/Ni coatings and nickel-based corrosion resistant alloys

  • Whole-life cycle costs of carbide coatings estimated to be 50% of hard chrome plating

Thermal spray is the preferred replacement for many applications of hard plating applications, such as the hard chrome plating of landing gear, and is increasingly being specified by companies that are environmentally aware.

The machining of landing gear involves the ultimate in precision

Permeate to innovate

Bodycote says it can also provide a range of organic sealants, plus its proprietary thin-film technology. The company’s technology uses ceramic to seal existing coatings, such as chrome and tungsten carbide. The ceramic seal thermo-chemically diffuses throughout the coating, chemically bonding to both the coating and the substrate and filling any micro-cracking and porosity with super-hard ceramic particles. The seal prevents corrosives from attacking the substrate via blistering and undermining of the coating.

Furthermore, the precision nature of ceramic coating and any associated thermal spray coating requires accurate measurement, finishing and quality inspection. Bodycote’s facilities are equipped with precision machining and finishing machines capable of coating removal for repair of worn components and post-coating finishing to ensure metallographic quality and integrity.

Regarding the kinds of rigorous testing procedures Bodycote processed parts undergo to ensure they pass airworthy regulations, all the testing of undercarriage parts and controlling heat treatment and surface technology specifications are developed by the OEMs. Indeed, Bodycote holds all relevant international and national aerospace quality accreditations, such as ISO 9001, AS 9100, ISO 14001 and Nadcap. It also possesses accreditations with all the major aerospace companies and has established a ‘preferred supplier’ status with many of them.



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