Product category:
Materials and components
News Release from: Bekaert Advanced Coatings | Subject: DylynPlus coatings
Edited by the Engineeringtalk Editorial
Team on 21 June 2006
Diamond-like carbon coatings cut
friction losses
Mark Boghe examines the benefits of low-friction DylynPlus coatings in automotive applications.
Engine designers are continually challenged to reduce mechanical friction losses in motor engines in order to improve motor engine performance: increasing oil costs, proliferating government regulations, and vigorous international competition make this essential The main%age (15-20%) of the energy expenditure generated within an internal combustion engine, according to studies, is made up of friction losses: piston skirt friction, piston rings and bearings, account for 66% of total friction losses, and the valve train accounts for 20-25% at low speed
This article was originally published on Engineeringtalk on 4 Jul 2006 at 8.00am (UK)
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The remainder of the losses come from crankshaft, transmission and gears.
Other challenging design considerations include reductions in wear, oil consumption and exhaust emissions.
Component problems from wear or friction usually start at the surface.
So when seeking a solution to protect this surface, coatings are the logical route to follow.
In fact, a wide range of coating solutions are available to designers and are increasingly used in the automotive industry.
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The main advantage of applying Bekaert DLC coatings is that it requires no structural changes to the engine design
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Among these coatings, diamond-like carbon coatings (DLC) show a combination of outstanding qualities: some DLC coatings are inherently self-lubricating and resistant to abrasive, adhesive and corrosive wear.
Unlike other surface treatments that either increase wear resistance or improve friction behaviour, DLC coatings make both properties available in a single surface treatment.
At the same time, DLC coatings possess a low coefficient of friction, a low surface energy approaching that of Teflon, and a hardness greater than that of carbide or titanium nitride (TiN).
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The result is a coating solution that provides a combination of unique wear and low friction.
Its excellent tribological properties are governed by the formation of a "transfer" layer on the contact surfaces of a-C:H coatings and their counterparts.
DLC coatings are a family of coatings made up primarily of carbon chains in an amorphous structure with sp2 (trigonal) and sp3 (tetrahedral) bondings.
Sp3 is the cubic form of carbon known as diamond, compared with sp2 that is graphite.
There are different types of DLC: hydrogen-free (a-C), hydrogenated (a-C:H) or metal-doped (Me-C:H) coatings.
These coatings are typically thin-film and are applied during a vacuum deposition process (PVD or CVD).
Bekaert has produced DLC coatings for more than 10 years in its Industrial Coatings Division and is a world leader in advanced metal transformation, advanced materials and coatings.
The Belgian-based firm realises 40% of its turnover in the automotive industry, and its DLC coatings are used in a variety of different applications (textile, semiconductor, plastic injection).
In the racing segment, Bekaert has achieved a leadership position with its Cavidur coatings, recognised as the defining standard in this sector.
The result of the unique synergy between the technological competences of the various Bekaert divisions, new DLC coatings suitable for large volume applications in the automotive sector have been developed and brought to the market as DylynPlus coatings.
DylynPlus is produced in Bekaert's proprietary large-scale equipment (vacuum vessel larger than 3m3, for example) which delivers a high and reproducible quality at a very low cost.
The DylynPlus is therefore well adapted to help the engineer to reduce mechanical friction losses in combustion engines.
The focus is first on the valve train components.
Components like tappets, camshafts, finger followers, and valves, are currently coated with DylynPlus.
Piston skirts, piston rings and wrist pins are other possible components.
The DylynPlus coating is an a-C:H coating with the following basic properties.
It has a low coefficient of friction less than 0.10 in a dry steel-ball-on-disc test run at 25C, 50% RH, pressure of 10N, speed of 0.17m/s and for 100,000 cycles.
DylynPlus features high hardness, up to 20GPa (measured by nano-indentation) with the possibility to tailor this hardness to fit the requirements of the application.
This high hardness guarantees a high abrasive wear resistance.
It features good adhesion, better than HF2 following the VDI 3198 norm and a critical value (Lc2) exceeding 25N in the scratch test (coating deposited on M2 steel for the both tests).
The temperature during the process is kept below 200C in order to avoid loss of parts hardness and distortion of parts.
And the typical thickness value is between 1 and 5um with a spreading of 15%.
The first property to draw attention is the extremely low coefficient of friction of DylynPlus, in dry as well as in lubricated conditions.
The ball-on-disc (BOD) test allows the determination and the study of the coefficient of friction under varying time, contact pressure, velocity, temperature, humidity, and lubrication conditions.
compared with uncoated substrates, to other coatings like TiN or CrN, or to other commercial DLC coatings, the DylynPlus has the lowest available coefficient of friction of about 0.05.
The DylynPlus coefficient of friction remains low in combination with different lubricants.
Different real engine tests have confirmed the results of the BOD tests.
These engine tests are particularly interesting because they show the real benefit of these coatings.
Most BOD measurements are done in dry conditions to show the effect of the low coefficient of friction, but this is not applicable as such for engine components which are operating in lubricated conditions.
Obviously, in full film lubrication conditions, the effect of the coating is as negligible as that of all the other coatings.
But in the boundary or mixed lubrication regime, as happens for example at engine low speed range for valve train components, the decrease of friction from using the DylynPlus is effective.
Besides reducing frictional losses or eliminating wear problems in existing systems, coating such as the DylynPlus enables the use of lighter materials to decrease the moving mass, and therefore fuel consumption.
Here again, the wear resistance and low friction properties of the coating are the key parameters.
To take full benefit of DylynPlus coating it is necessary to consider the use of these coatings at the beginning of the development phase.
In order to have an optimal design, the substrate has to be selected in relation to the function of the coating.
Parameters like substrate material, heat treatment and surface roughness are of prime importance to allow the coating to reach its maximum performance.
Bekaert can assist designers to make the most effective choices to reduce their overall design time.
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