Dr. Yuri Zhuk, Hardide Coatings05.09.16
In all industries, problem solving, technology developments, and challenging standard practices are key to improving performance. In extreme environments, or when wear is an issue, the challenge is to maintain high performance while ensuring economic viability.
In the aerospace industry, leak-tightness of aircraft hydraulic actuators and rotating shafts depends on seals. In abrasive and corrosive environments, metal seal track or piston rod surface finish degradation can accelerate the rate of seal wear by an order of magnitude. In addition to rotating parts being subject to wear, aerospace components are subject to extremes in temperature depending on the location of the aircraft.
Use of hard, wear-resistant coatings can help increase the component life, improve dimensional stability and quality of the surface finish and, as a result, prevent premature wear of the seal. This can help reduce downtime cost and improve overall competitiveness.
We, as innovators in advanced surface coating technology, have developed a range of surface engineering solutions to help industry solve problems, improve efficiency and reduce downtime. Hardide coatings are advanced nano-structured tungsten carbide coatings applied by low-temperature CVD (chemical vapor deposition). Providing exceptional wear and corrosion resistance combined with toughness and ductility, these patented coatings add value to components and reduce operational costs by saving downtime, increasing productivity and improving performance.
Engineering a Solution
Hard chrome plating (HCP) has been widely used in the aerospace industry for many years. However, its production process is being banned in September 2017 under EU REACH environmental and health and safety regulations, unless otherwise authorized by the EU Commission, as HCP uses carcinogenic hexavalent chromium salts in its production. Increasingly tight restrictions are also being imposed in the United States by OSHA.
A number of Hardide coating variants are available to solve various problems such as wear, corrosion or galling. Coatings are selected based on the individual application and/or operating environment, and can also be tailored to specific requirements. Hardide-A matches the standard thickness (50 – 100 microns) and hardness (800 – 1200 Hv) of HCP, simplifying the transition without the need for dimensional changes or drawing re-design. HCP’s intrinsic performance limitations hinder its more demanding wear applications. Hardide-A outperforms it in several key areas including enhanced protection against corrosion, wear, and chemically aggressive media, improved fatigue life and a non-porous structure.
Other alternatives to HCP are available including thermal spray, in particular high-velocity oxy-fuel (HVOF), and emerging processes such as electroless-nickel composite plating, explosive bonding, electro-deposited nanocrystalline cobalt-phosphorus alloys and physical vapor deposition (PVD) coatings. To date, HVOF and other spray coatings have been considered the best available alternative to HCP. Although successful in some applications, each coating has limitations.
Thermal spray coatings can build a very thick and durable layer, but the resultant coatings are rough and porous in structure and often require post-coating grinding which is not possible on intricate shapes. PVD coatings can produce an extremely hard layer with accurately controlled thickness, but they are very thin, typically less than four microns, and have limited load-bearing capacity. However, Hardide-A provides several advantages over HVOF such as the ability to coat complex geometric shapes and internal bores, improved corrosion and fatigue resistance, a smooth as coated low-friction surface and ease of finishing.
The Coating Process
CVD coatings are crystallized from the gas phase atom-by-atom in a vacuum chamber reactor at a temperature of approximately 935o F, producing a conformal coating which can coat internal and external surfaces and complex shapes. The coatings are a metallic tungsten matrix with dispersed nano-particles of tungsten carbide typically between 1 and 10 nanometers in size. Dispersed tungsten carbide nano-particles give the material enhanced hardness which can be controlled and tailored to give a typical hardness range between 800 and 1200 Hv and, with some types of Hardide coating, up to 3500 Hv. Abrasion resistance is up to 12 times better than hard chrome, 500 times better than Inconel and 4 times better than HVOF tungsten carbide.
The CVD coating is applied by a batch process and can be polished to Ra 0.2 – 0.3 microns (8-12 micro-inches) or super-finished to Ra 0.02 (0.8 micro-inches) without the need for grinding. This finish does not degrade over time and is a very effective and ‘friendly’ counterface to seals as it protects metal shafts or plungers from scratching and scoring that can result from rotation or reciprocation and which can accelerate the seal wear. Unlike HVOF, the Hardide coating is free from a cobalt binder which can be leached from the thermal spray coating in a corrosive environment leaving a rough and abrasive surface. As a result, the CVD coated metal counter-surface against which the seal operates retains a good finish in operation for longer - even in an abrasive or corrosive environment - and is less abrasive for the seal.
When dimensional accuracy is required, the coatings can be diamond ground and super finished for critical bearing surfaces.
CVD Tungsten Carbide Applications
Changes in technology are also driving the need for an alternative to traditional coating materials. The ability to print 3D components means that manufacturers can seamlessly join parts together to make one larger, more complex component. These more complicated shapes cannot be fully coated with line-of-sight techniques, such as HVOF, but internal surfaces can be coated with CVD.
Hardide tungsten carbide coatings have been used on Eurofighter Typhoon jet components since 2005 and were recently technically approved by Airbus as a potential alternative to HCP on some specific Airbus aircraft components. It met the Airbus requirements for thick CVD tungsten carbide coatings and is a suitable alternative for hard chrome plating and HVOF applied coatings. The coatings are also undergoing hard chrome replacement tests with European helicopter manufacturer AgustaWestland, and a variety of tests for other applications in the sector.
Other typical aerospace applications include pins, bushes, bearings, hooks, catches, landing gear, flap tracks and slats, sleeves, rods, valves, pistons, actuators, compressors, shafts, hydraulic and pneumatic cylinders.
CVD tungsten carbide coatings also show good potential for use in the space sector, particularly for satellites. The Hardide coating has shown no signs of fracture after 100 nano-impact tests, which means that its fracture toughness can protect the components. Titanium and other metals in vacuum can lose their protective oxide layer and any moving metal parts can suffer from galling. The coefficient of friction of the CVD coating is the same in a vacuum as it is in an ambient environment and the coating can provide excellent anti-galling protection for moving joints such as robotic arms.
Benefits of CVD Coatings
In industries where equipment and tools are pushed to the extreme of their operating capacity, companies are seeking ways to improve performance while delivering a reduction in downtime and meeting environmental regulations.
Challenging environments – such as exposure to chemicals, heat, abrasion, friction and corrosion – put pressure on the equipment, leading to failure of critical components, downtime and loss of productivity. Our range of tungsten carbide CVD coatings provides an effective solution for these problems, ensuring extended life of components and less time spent on maintenance.
Using the latest materials technology, the tungsten carbide CVD coatings are a game-changing evolution in performance, not just an improvement of existing coatings. The use of this CVD process opens the door to enable a level of engineering flexibility that is not possible with alternative technologies.
In the aerospace industry, leak-tightness of aircraft hydraulic actuators and rotating shafts depends on seals. In abrasive and corrosive environments, metal seal track or piston rod surface finish degradation can accelerate the rate of seal wear by an order of magnitude. In addition to rotating parts being subject to wear, aerospace components are subject to extremes in temperature depending on the location of the aircraft.
Use of hard, wear-resistant coatings can help increase the component life, improve dimensional stability and quality of the surface finish and, as a result, prevent premature wear of the seal. This can help reduce downtime cost and improve overall competitiveness.
We, as innovators in advanced surface coating technology, have developed a range of surface engineering solutions to help industry solve problems, improve efficiency and reduce downtime. Hardide coatings are advanced nano-structured tungsten carbide coatings applied by low-temperature CVD (chemical vapor deposition). Providing exceptional wear and corrosion resistance combined with toughness and ductility, these patented coatings add value to components and reduce operational costs by saving downtime, increasing productivity and improving performance.
Engineering a Solution
Hard chrome plating (HCP) has been widely used in the aerospace industry for many years. However, its production process is being banned in September 2017 under EU REACH environmental and health and safety regulations, unless otherwise authorized by the EU Commission, as HCP uses carcinogenic hexavalent chromium salts in its production. Increasingly tight restrictions are also being imposed in the United States by OSHA.
A number of Hardide coating variants are available to solve various problems such as wear, corrosion or galling. Coatings are selected based on the individual application and/or operating environment, and can also be tailored to specific requirements. Hardide-A matches the standard thickness (50 – 100 microns) and hardness (800 – 1200 Hv) of HCP, simplifying the transition without the need for dimensional changes or drawing re-design. HCP’s intrinsic performance limitations hinder its more demanding wear applications. Hardide-A outperforms it in several key areas including enhanced protection against corrosion, wear, and chemically aggressive media, improved fatigue life and a non-porous structure.
Other alternatives to HCP are available including thermal spray, in particular high-velocity oxy-fuel (HVOF), and emerging processes such as electroless-nickel composite plating, explosive bonding, electro-deposited nanocrystalline cobalt-phosphorus alloys and physical vapor deposition (PVD) coatings. To date, HVOF and other spray coatings have been considered the best available alternative to HCP. Although successful in some applications, each coating has limitations.
Thermal spray coatings can build a very thick and durable layer, but the resultant coatings are rough and porous in structure and often require post-coating grinding which is not possible on intricate shapes. PVD coatings can produce an extremely hard layer with accurately controlled thickness, but they are very thin, typically less than four microns, and have limited load-bearing capacity. However, Hardide-A provides several advantages over HVOF such as the ability to coat complex geometric shapes and internal bores, improved corrosion and fatigue resistance, a smooth as coated low-friction surface and ease of finishing.
The Coating Process
CVD coatings are crystallized from the gas phase atom-by-atom in a vacuum chamber reactor at a temperature of approximately 935o F, producing a conformal coating which can coat internal and external surfaces and complex shapes. The coatings are a metallic tungsten matrix with dispersed nano-particles of tungsten carbide typically between 1 and 10 nanometers in size. Dispersed tungsten carbide nano-particles give the material enhanced hardness which can be controlled and tailored to give a typical hardness range between 800 and 1200 Hv and, with some types of Hardide coating, up to 3500 Hv. Abrasion resistance is up to 12 times better than hard chrome, 500 times better than Inconel and 4 times better than HVOF tungsten carbide.
The CVD coating is applied by a batch process and can be polished to Ra 0.2 – 0.3 microns (8-12 micro-inches) or super-finished to Ra 0.02 (0.8 micro-inches) without the need for grinding. This finish does not degrade over time and is a very effective and ‘friendly’ counterface to seals as it protects metal shafts or plungers from scratching and scoring that can result from rotation or reciprocation and which can accelerate the seal wear. Unlike HVOF, the Hardide coating is free from a cobalt binder which can be leached from the thermal spray coating in a corrosive environment leaving a rough and abrasive surface. As a result, the CVD coated metal counter-surface against which the seal operates retains a good finish in operation for longer - even in an abrasive or corrosive environment - and is less abrasive for the seal.
When dimensional accuracy is required, the coatings can be diamond ground and super finished for critical bearing surfaces.
CVD Tungsten Carbide Applications
Changes in technology are also driving the need for an alternative to traditional coating materials. The ability to print 3D components means that manufacturers can seamlessly join parts together to make one larger, more complex component. These more complicated shapes cannot be fully coated with line-of-sight techniques, such as HVOF, but internal surfaces can be coated with CVD.
Hardide tungsten carbide coatings have been used on Eurofighter Typhoon jet components since 2005 and were recently technically approved by Airbus as a potential alternative to HCP on some specific Airbus aircraft components. It met the Airbus requirements for thick CVD tungsten carbide coatings and is a suitable alternative for hard chrome plating and HVOF applied coatings. The coatings are also undergoing hard chrome replacement tests with European helicopter manufacturer AgustaWestland, and a variety of tests for other applications in the sector.
Other typical aerospace applications include pins, bushes, bearings, hooks, catches, landing gear, flap tracks and slats, sleeves, rods, valves, pistons, actuators, compressors, shafts, hydraulic and pneumatic cylinders.
CVD tungsten carbide coatings also show good potential for use in the space sector, particularly for satellites. The Hardide coating has shown no signs of fracture after 100 nano-impact tests, which means that its fracture toughness can protect the components. Titanium and other metals in vacuum can lose their protective oxide layer and any moving metal parts can suffer from galling. The coefficient of friction of the CVD coating is the same in a vacuum as it is in an ambient environment and the coating can provide excellent anti-galling protection for moving joints such as robotic arms.
Benefits of CVD Coatings
In industries where equipment and tools are pushed to the extreme of their operating capacity, companies are seeking ways to improve performance while delivering a reduction in downtime and meeting environmental regulations.
Challenging environments – such as exposure to chemicals, heat, abrasion, friction and corrosion – put pressure on the equipment, leading to failure of critical components, downtime and loss of productivity. Our range of tungsten carbide CVD coatings provides an effective solution for these problems, ensuring extended life of components and less time spent on maintenance.
Using the latest materials technology, the tungsten carbide CVD coatings are a game-changing evolution in performance, not just an improvement of existing coatings. The use of this CVD process opens the door to enable a level of engineering flexibility that is not possible with alternative technologies.