Andreas LESON, et al.
Laser-Arc Coating vs Friction
Laser-arc deposited tetrahedral amorphous
carbon coating eliminates friction
Jun 08, 2015
Diamond-like coatings save
Dr. Volker Weihnacht, Prof. Andreas Leson and Dr.
Hans-Joachim Scheibe (left to right) successfully developed a
laser arc method of depositing friction-reducing, wear-resistant
coatings on components. Credit: Dirk Mahler/Fraunhofer
Coating engine components with hard carbon reduces friction to
almost zero – a development that could save billions of liters of
fuel worldwide every year. Now researchers have developed a new
laser method to apply the coating on the production line
Scientists already know how to coat components with diamond-like
carbon to minimize friction. But now Fraunhofer researchers have
developed a laser arc method with which layers of carbon almost as
hard as diamond can be applied on an industrial scale at high
coating rates and with high thicknesses. By applying carbon
coatings to engine components such as piston rings and pins, fuel
consumption can be reduced. "Systematic application of our new
method could save more than 100 billion liters of fuel each year
over the next ten years," says Prof. Andreas Leson from the
Fraunhofer Institute for Material and Beam Technology IWS in
Dresden, referencing a study that was published in the journal
Tribology International in 2012.
Carbon-based coatings are already used in volume production. But
now the team of IWS researchers led by Prof. Leson, Dr.
Hans-Joachim Scheibe and Dr. Volker Weihnacht has succeeded in
producing hydrogen-free ta-C coatings on an industrial scale at a
consistent level of quality. These tetrahedral amorphous carbon
coatings are significantly harder and thus more resistant to wear
than conventional diamond-like coatings. "Unfortunately, you can't
just scrape off diamond dust and press it onto the component. So
we had to look for a different method," says Dr. Scheibe, who has
spent over 30 years investigating carbon's friction-reducing
A pulsed laser controls the light arc
In a similar style to old-fashioned film projectors, the laser arc
method generates an arc between an anode and a cathode (the
carbon) in a vacuum. The arc is initiated by a laser pulse on the
carbon target. This produces a plasma consisting of carbon ions,
which is deposited as a coating on the workpiece in the vacuum. To
run this process on an industrial scale, a pulsed laser is
vertically scanned across a rotating graphite cylinder as a means
of controlling the arc. The cylinder is converted evenly into
plasma thanks to the scanning motion and rotation. To ensure a
consistently smooth coating, a magnetic field guides the plasma
and filters out any particles of dirt.
The laser arc method can be used to deposit very thick ta-C
coatings of up to 20 micrometers at high coating rates. "High
coating thicknesses are crucial for certain applications –
especially in the auto industry, where components are exposed to
enormous loads over long periods of time," says Dr. Weihnacht.
The automotive and motorcycle manufacturer BMW is working
intensively on the industrial-scale implementation of ta-C engine
components in its various vehicle models with the aim of reducing
their fuel consumption. Prof. Leson sees this as the first major
step in using the laser arc method to save resources. And as a
motorcycle aficionado himself, he also sees another positive
effect stemming from this development: "The fact that our research
is helping to make motorcycling more environmentally friendly
eases my conscience every time I go for a ride," he says, unable
to suppress a smile.
Andreas Leson, Hans-Joachim Scheibe and Volker Weihnacht received
the 2015 Joseph von Fraunhofer Prize for the development of the
laser arc method and the application of ta-C coatings in volume
METHOD OF PRODUCING AN ANTI-WEAR LAYER AND ANTI-WEAR LAYER
PRODUCED BY MEANS OF SAID METHOD
The invention concerns the production of anti-wear layers disposed
on surfaces of internal combustion engine components which are
exposed to frictional wear. According to the method, anti-wear
layers are formed on the particular surface by means of electrical
arc discharge under vacuum conditions. The anti-wear layers are
formed from at least approximately hydrogen-free, tetrahedral
amorphous (ta-C) carbon consisting of a mixture of sp2 and sp3
hybridized carbon, and have a microhardness of at least 3500 HV
and an arithmetic mean surface measure Ra of 0.1 [mu]m, without
mechanical, physical and/or chemical surface treatment.
A process for producing a wear protection layer and prepared by
the process wear protection layer
The invention relates to a method for the production of
wear-resistant coatings which have been formed on surfaces of
components of internal combustion engines which are subjected to
frictional wear by means of electric arc discharge under vacuum
conditions on the respective surface, and produced with the method
of wear-resistant coatings.
The wear-resistant coatings are made wasserstrofffreien,
tetrahedral amorphous from sp <2> and sp <3>
hybridized carbon (ta-C) formed.
It has been shown that these types of layers in which a maximum
hydrogen content of 1 atomic%, preferably not more than 0.5
atomic% still want to allow, have particularly favorable wear and
It was therefore suggested that these layers are on a variety of
surfaces of components subject to wear of internal combustion
engines, as for example piston rings, tappets, cams of camshafts
or piston pin to use.
This layers have a high hardness and therefore increased wear
The attainable friction at a sliding action on the surface of a
not so coated base or GE genkörpers are low, so that this will
affect the economic operation and the C02 footprint advantageous
Such layers can with different PVD vacuum coating process using a
graphite cathode are made.
It has been found that an especially high deposition rate can be
achieved in the process, can be reached in which electric arcs
between an anode and a cathode formed from graphite.
In these methods, but it is disadvantageous that in the coating
larger particles or even so-called droplets are formed which are
deposited in the layer and the surface properties are thereby
adversely affected, so that the surface must be leveled by a post.
This prepares in layers, which have a particularly high hardness,
but significant problems that cure especially in micro- above 5000
HV detrimental because an extremely high time expenditure is
required to obtain sufficiently smooth surfaces of these layers
for a favorable sliding behavior to.
Is particularly suitable for the formation of such hard layers
called the Laser-Arc process in which an electric arc in a vacuum
by means of a pulsed laser beam ignited and with the on
Arc obtained plasma of ionized particle flow in this, the ionized
particles can be deposited out to a substrate and a coating,
This type of layers may, however also in a per se known method, in
which an electrical arc discharge is in the vacuum for generating
the plasma used without the Are arc discharge is initiated by a
laser beam applied.
Here, the arc in known manner either be ignited only by a
sufficiently high voltage between an anode and a cathode connected
as a target and, secondly, there is the possibility that ignition
means of electrically conductive ignition elements due
These known methods, however, have the disadvantage that their
plasma is relatively rich in droplets and particles.
However, possibilities have been proposed to counter this
drawback, to perform a so-called "filtering" of the plasma for
storage of particles.
Several options for this are available from BF Coli and DM Sanders
in "Design of Vacuum arenes based Sources"; Surface and Coatings
Technology ", No. 81 (1996) 42-51 described.
This is based on these known solutions, the fact that using
magnetic fields, the ionized light components of a plasma can be
deflected and, because of their unfavorable Droppings charge /
mass ratio, serious deflectable particles can be separated from
each other substantially larger.
However, these filter assemblies have some significant
The design of these systems is very complex and expensive.
The diameter of the magnetic filter and thus the diameter of the
coating surface is limited due to the strong magnetic fields
needed and of the necessary electrical power to about 150 mm.
The coating rate of the process is reduced to approximately 15-20%
compared to that without use of the magnetic filter.
For processes in which electric arcs are used for coating, is in
EN 2006 10 009 160 AI to use an absorber electrode and proposed by
magnets to separate larger particles from a plasma and thus
prevent these settle in the coating and characterized the surface
geometry is adversely affected.
However, no layers are known, which are formed from hydrogen-free
tetrahedral amorphous from sp <2> and sp <3>
hybridized carbon (ta-C), which have increased hardness, while
very good sliding friction at the same time, taking on component
surfaces with a increased deposition rate by means of electric arc
discharges have been deposited without subsequent surface
treatment, which leads to leveling of surveys and reduce the
roughness, must be carried out.
It is therefore an object of the invention to provide a
wear-resistant coating for stressed on sliding surfaces of
components of internal combustion engines are available, having an
improved wear resistance and simultaneously improved sliding
properties, the production can be effected with reduced effort and
increased deposition rate by means of electric arc discharges.
According to the invention this object is achieved with the
features of claim 1.
The claim 7 relates to the method produced wear-resistant
Advantageous refinements and developments of the invention can be
used with features that are in the subordinate claims referred
With the inventive method wear protective layers on surfaces of
internal combustion engines, which are exposed to frictional wear,
Here, a plasma by pulsed laser irradiation sequentially ignited
electric arc discharges in vacuum conditions, in which the
electric arc discharge between an anode and a cathode are operated
as graphite formed.
There are ionized parts of the plasma as a layer consisting of at
least approximately hydrogen-free, tetrahedral amorphous (ta-C),
consisting of a mixture of sp <2> and sp <3>
hybrisiertem carbon (ta-C according to VDI
Be in 2840) formed and deposited on a surface of at least one
Positively charged ions of the plasma are moved by means of an
absorber electrode toward the at least one component.
In this case, the same voltage is applied to at least
approximately the anode and the absorber electrode.
While the electrical arc discharges can be operated to flow
through the absorber electrode, an electric current of at least
1.5-fold greater, preferably at least two times greater than the
electrical generic current flowing through the anode, is.
There is no mechanical and / or chemical post-processing of the
coated surface of the at least one component, which results in a
smoothing of the surface is carried out.
A subsequent smoothing of the surface of the formed wear
protection layer is not particularly influencing the current
flowing through the anode electrode and the absorber respectively
different electric current through the loading required.
Advantageously, the plasma is formed within a laser arc chamber
and a vacuum chamber in which the at least one component is
arranged, directed versa.
The laser arc chamber can be flanged to the vacuum chamber.
In the laser arc chamber, a vacuum is also respected.
By means of the absorber electrode should be as deflected
positively charged ions of the plasma, that it, starting from the
cathode do not directly
Way impinge on the surface of the at least one component and
electrons move from the plasma toward the absorber electrode, so
that they move not possible or with a small number in the
direction to be coated component surface.
With at least one arranged arc discharge or sputter source, which
is arranged in the vacuum chamber, a thin adhesive layer on the at
least one component may be deposited.
Advantageously, an absorber electrode used with a plurality of
Larger droplets or droplets can be discharged between the Streif
s, so that it does not impinge on the surface of the at least one
A movement direction of droplets inducing reflection can be
The wear-resistant coating according to the invention is produced
on surfaces of internal combustion engines that are subjected to
frictional wear, trained.
They have been trained by means of electric arc under vacuum
conditions on the respective surface, and are made of at least
approximately hydrogen-free, tetrahedral amorphous (TAC)
consisting constituted <3> hybrisiertem carbon from a
mixture of sp <2> and SP.
Preferably, they can be formed with the aforementioned
The wear-resistant coating has a microhardness of 3500 HV and an
arithmetic mean roughness Ravon 0.1 µ?? on.
Here no subsequent mechanical, physical and / or chemical surface
treatment is necessary in order to comply with this roughness can.
The wear-resistant coating according to the invention can
advantageously have produced µ?? also an average roughness Rzvon
The total averaged roughness Rzentspricht the arithmetic mean of
all readings Einzelrau- deep.
The wear-resistant coating according to the invention produced
should a reduced peak height Rpkvon µ?? maximum of 0.35,
preferably a maximum of 0.25 µ??.
This value is in particular from the standpoint of reduced
friction, and therefore are beneficial.
Both the arithmetic average roughness Ra, as well as the other two
roughness R2undPkkönnen be determined with the known profile
Here, a probe tip that is preferably made of diamond, and a small
tip radius should have, be used.
It if the wear protective layer has a microhardness of 3500 HV,
preferably 4000 HV, more preferably at least 5000 HV, preferably
of at least 5700 HV and most preferably from 6000 HV and
preferably a roughness Rakleiner 0.08 µ?? is particularly
favorable, more preferably less than 0.05 m_aufweist, whereby the
wear resistance and the durability can be further improved or
For the hardness measurement may be achieved in a device
"FISCHERSCOPE H100C XYP" from Helmut Fischer GmbH & Co. KG be
The test load should be chosen so that the penetration depth of
the indenter is a maximum of 1/10 of the film thickness.
With an inventively produced wear-resistant coating on the piston
pin, in a tribological system consisting of counter-body
connecting rod with sleeve (brass) and aluminum pistons with a
vibration friction wear tribometer with piston pin module from
Optimol Instruments Prüftechnik GmbH a coefficient of friction
less than 0.03, preferably less than 0.025 can be achieved.
This is the case with oil-lubricated tests in a temperature range
between 100 ° C and 130 ° C, as is typical for components of
internal combustion engines, too.
The friction coefficient changes only slightly over the lifetime
of the coated component, whereby a reduction in the coefficient of
friction could be detected after a short running time.
The wear rate can be reduced by a factor of 3 compared to
conventional DLC coatings.
The proportion of SP should be <3> hybridized carbon
preferably well above 40%, above 50%.
In addition, should the anti-wear layer no other chemical
elements, such as metals or halogens or Phosphorus be included.
This also applies to chemical compounds.
This only an inert gas such as argon and no particular hydrocarbon
compound should be included in the laser chamber and Are in the
vacuum chamber, if necessary.
The layer thicknesses should be at least 0.5 µ??, preferably at
least 2 µ?? or more.
Advantageous may have been formed on the surface to be coated at
least one adhesive and / or intermediate layer, on which then a
wear-resistant layer of the invention is formed.
For this purpose, for example, be chosen µ?? a chromium layer
having a thickness of at least 0.1.
In the preparation may advantageously a cylindrical cathode
(target) can be used made of graphite, which rotates during the
process about its longitudinal axis, so that the respective base
points of the electrical arc discharges extend over the entire
surface of the cathode, thereby achieving a geleich- excessive
removal of carbon can be.
Ignition of GE pulses powered electrical arc discharges with a
laser beam, the laser beam can be also operated in a pulsed
accordingly and deflected so that it impinges at various
predetermined positions on the surface of the cathode and there as
a result of the energy input an electrical see arc discharge at
each laser pulse, can be ignited.
The electrical voltage between an anode and the cathode is
controlled so that the arc will go out again in each case after a
predetermined time to subsequently burn at a different position, a
new arc discharge.
The layer thickness of a wear-resistant coating can be formed by
means of the number of unused electric arc discharges, are
affected with a known size of a surface to be coated.
Other process parameters should, however, be kept as constant as
With the parameters of electrical current and voltage with the
electric arc discharges are operated whose duration, the pulse
rate and one on a component to be coated (substrate) during the
arc pulse applied bias voltage can also affect the trainees layer
This concerns in particular the layer structure and in particular
the proportions of sp <2> and sp <3> hybridized
So electric currents above 1000 A, are preferably used above 1500
A and a pulse frequency of between 300 Hz and 600 Hz can be
There may be a bias voltage at - 50 V to - 200 V, preferably 100 V
is applied to the component to be coated in the field.
Thus, an electric current of 500 A ± 100 A can flow through the
absorber electrode (preferably ± 50 A) through the anode and of
1100 ± 100 A A (preferably ± 50 A), when electrical arc discharges
are ignited and operated.
Operation of electric arc discharges can be performed with a pulse
duration in the range 250 to 600 µ $ µ5.
A termination of the electrical arc discharges can be achieved by
reducing the electrical voltage at least at the anode.
An ignition of electric arc discharges according to a pulsed
carried out irradiation of the surface of the cathode with a
directed laser beam to the surface may take place at an increased
electrical voltage, which is reduced after the ignition of the
respective electric arc discharge.
In the coating apparatus should be used, with the larger particles
are prevented from impinging on the surface to be coated.
This can each alone, be an absorber electrode.
In this case, a structure may be used as it is 10 2006 009 160 AI
known from DE, the disclosure of which reference in its entirety
is incorporated herein.
In this case, at least one permanent magnetic element is inserted,
which is aligned parallel to the rotation axis of the cathode and
parallel to the surface of a cathode.
In addition, while an absorber electrode is available with which
an electric field is formed, is passed through the electric arc
formed by the discharge plasma.
With both the / the Permaentmagnetelement (s), as well as with the
absorber electrode larger particles contained in the plasma can
thus be influenced in their movement, particularly in its
direction of movement that they do not impinge on the surface to
be coated or there at an angle, the one Installation avoids into
Additionally, at least one aperture between the surface to be
coated of a part and the cathode may be arranged through which the
plasma, the carbon ions, which can be used for layer formation,
containing is performed in the direction of the surface to be
The absorber electrode can be arranged in the direction of
movement of the plasma by a diaphragm and / or anode.
A Permant magnet element may for example be arranged in the shade
of a diaphragm or a diaphragm element.
The invention will be described in closer detail.
Figure 1 shows in schematic form the structure of a device for the
Education is inventive wear-resistant coatings suitable.
Figure 1 showed a vacuum coating system with a vacuum chamber 1 in
fixed rotational device to be coated components 14 and thus both
with double and triple rotation can be coated.
In the vacuum chamber 1 are known or arc discharge Sputter 2 or a
combination of both for plasma etching or the deposition of a thin
adhesive layer present.
In the vacuum chamber 1, a laser arc chamber is flanged 3 with
rotating graphite roll as KathodelO and a film pull 11 to protect
the laser entrance window before steaming.
In direction of the vacuum chamber 1, a filter module 4, with
service door and internal structure of the absorber-anode
arrangement 5, 6, and side-mounted permanent magnet arrangement 7
Furthermore, a scanner and focusing with laser entrance window 8
for linear guidance of the laser beam 9 over the full length of
the cathode laser arc chamber 3 available.
By the reference numeral 12, the path consisting of the means of
electric arc discharge between the cathode 10 and the anode 6
selected from the generated plasma larger particles towards the
absorber electrode 5 is illustrated with an arrow.
The electric arc discharges are ignited by means of the
deflectable laser beam 9 on the surface of the cathode 10, which
consists of 99.9% graphite.
Here, the cathode 10 is rotated about a rotation axis that is
aligned perpendicular to the plane of the drawing and the laser
beam 9 is deflected along this axis of rotation.
Thereby, a uniform removal of cathode material and at the same
time a large area to be coated in the vacuum chamber 1 can be
The absorber electrode 5 is electrically connected to a positive
It is provided with a plurality of electrically conductive
strip-shaped elements which are arranged at a distance from each
other, are formed.
Between the strip-like elements column formed by the larger
particles can be performed.
The Bezugszeichenl3 illustrates the path of the deflected carbon
ions of the plasma to the rotation device with the components to
be coated 14 with an arrow.
When the formation of the wear-resistant coatings on the surfaces
of the components 14 to be coated preferably with threefold
After evacuation of the vacuum chamber 1 and performing the
surface cleaning and activation a Cr adhesion layer having a
thickness of about 0.1 micron is deposited by sputtering.
Following the deposition of ta-C layer is to a thickness of about
Due to the selected parameters of pulsed laser arc source,
electric arc current 1600 A, pulse duration 350 ps at a frequency
of 520 Hz in combination with the adapted to the laser arc source
substrate-bias parameters in a high voltage range of - 800 V with
a pulse length of 350 ps and a low voltage of - 100 V at a pulse
length of 200 ps, ??very hard and smooth ta-C coatings with high
adhesion to the component surface (Rc 1) are deposited.
There is a distribution of the electric current, wherein 1100 A
flowing through the absorber electrode 5 and the anode 6 through
The anode 6 is arranged closer to the cathode 10, as the facing in
the direction of the cathode 10 the base of the absorber electrode
The specific means of profilometer roughness, are as follows: Raim
means 0.09 pm, Rzim means 1.0 pm and 0.28 pm Rpkim means.
The determined by Fischerscope microhardness of the wear-resistant
coating amounts to 7040 HV or the specific means LAWave modulus is
In vibration-friction-wear tribometer with piston pin module from
Optimol Instruments Prüftechnik GmbH a friction coefficient of
0.022 with an inlet oil OW30 the company Castrol, as lubricant was
The wear rate was reduced to approximately 30% compared to
conventional DLC coatings.
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