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Emerald Group Publishing Limited
Copyright © 2008, Emerald Group Publishing Limited
DLC breakthrough for internal surfaces on flying parts
Article Type: Materials From: Aircraft Engineering and Aerospace Technology: An International Journal, Volume 80, Issue 5
Tecvac Ltd of Swavesey, Cambridge, a member of the Wallwork Group, now offers a diamond-like carbon (DLC) coating on the internal surfaces of flying parts and aerospace engine components (Figure 1). DLC coatings can be applied to the internal surfaces of bores, tubes and hydraulic cylinders.
InnerArmor, an enhanced plasma coating process, will apply DLC coating up to 50 μm thick to the internal surfaces of tubes and bores up to 3 m in length. The DLC coatings are said to be inert and environmentally friendly. They claim to reduce friction losses to very low levels, and provide a very hard corrosion-resistant film.
Tecvac has already identified aerospace coating applications in control systems, fluid engineering, fuel management and delivery and hydraulics systems, and expects to find many other internal applications, especially bores in engine sub-systems where DLC coating has previously proved difficult or impossible to apply.
The InnerArmor process creates DLC surfaces with a “glass-like” amorphous (non-crystalline) structure, free from pinhole defects, even in tube lengths of 3 m at aspect ratios of 1:45. This is said to provide internal bores and tubes with very high levels of protection from erosion, scaling and fouling, and prevents adhesion from gases, liquids, powders and slurries.
According to Tecvac, InnerArmor DLC coatings can be conducting or insulating, and can withstand high loads at operating temperatures of 450°C. Coating application temperatures for a variety of formulations are below 200°C. This enables many hollow engine parts to be coated with DLC, and allows the replacement of expensive high-performance alloys with lower specification steels.
Tests with the new InnerArmor DLC process reportedly demonstrated superlative corrosion resistance and wear performance, and consistent film hardnesses of 3,000 HV. High performance was shown in salt spray tests to meet US standards. Very high-wear resistance in these tests was indicated by a very low attrition rate of less than 0.0005 μm/h. Tecvac can coat internal bores to thicknesses of between 5 and 50 μm.
The InnerArmor internal surface coating process, developed by Sub-One Technology Inc., combines the technologies of plasma vapour deposition and metallic and ceramic sputtering. It is claimed to be the first process to achieve high integrity internal surface coatings of DLC.
The hollow work piece is used as the vacuum chamber by sealing tube ends, connecting an anode to the openings, and arranging the circuit so that the walls of the work piece form the cathode. Known as the hollow cathode plasma ion immersion process, the operating system can be arranged to provide surface cleaning using an argon atmosphere, and apply multiple layers of a variety of materials, including DLCs. The process is covered by the recent US Patent 1091983.
The InnerArmor process is said to allow the effective placement of high integrity, very lubricious and extremely hard coatings that reach the complex cavities in pipe work and internal lumens or bores. The process claims to provide superior film bonding compared with other deposition methods. It also claims to provide all interior bore coating applications a high performance environmentally friendly process that offers the highest levels of corrosion protection, wear resistance, and energy efficiency.