Deliverables
For the multilayer system H-Nanocoat 1 (Cr+W-C:H) an automatically working coating system was developed to produce this layer system without any problems on all the interfaces between substrate and layer system, as well as between the different layers in the coating system. It has been shown that hardness, layer structure and layer thickness are to be tuned to the application. This technology is existing as part of a software package to control the production machine.
For the multilayer system H-Nanocoat 2 (Cr-W:H with a top layer of diamond-like carbon) an automatically working coating system was developed to produce this layer system without any problems on all the interfaces between substrate and layer system, as well as between the different layers in the coating system. It has been shown that hardness, layer structure and layer thickness are to be tuned to the application. A precursor system to be used for MS and HMDSO has been added to the system for development of Si-doped diamond-like carbon layers. This technology is existing as part of a software package to control the production machine.
A PVD coating technology was developed that allows the deposition of nanostructured carbon coatings for demanding tribological applications. The coating can be deposited by vacuum-arc discharge from graphite sources in dedicated PVD coating machines. There was developed a pulsed arc technique allowing for high-rate deposition of good-quality C/C-ML films in the thickness range 100 nm - 10 µm. The films can be deposited on complex three-dimensional metal substrates as steel components and tools. The periodicity is obtained by periodical change of deposition parameters influencing the energy of depositing carbon species.
The developed Carbon/Carbon multilayer (C/C-ML) is a coating for protecting metallic surfaces from wear and to reduce the friction force under tribological loading. It is a nanostructured amorphous coating consisting of 100% carbon. The layered nanostructure is obtained by periodic variation of chemical bonding state (sp-hybridization) between carbon atoms.
The film is composed of nanometre-layers with dominating sp3-content (diamond bonding) and dominating sp2-content (graphite bonding). Irrespective of partial graphite bonding the overall coating hardness is high (>40 GPa) resulting in extraordinary good wear resistance. The nanostructured C/C-ML is predestined for tribological application under demanding mechanical loading conditions. The films have high potential for low-wear and low-friction application e.g. on components in automotive industry. The special benefit of the coatings is the extremely low friction and wear under dry and mixed lubrication conditions.
Cr based coatings (Hauzer and Microcoat) and carbon based coatings (Hauzer and FhG IWS) were created, which showed much better tribological behaviour in the dry and lubricated contact with steel than steel surfaces.
The friction without lubrication measured in the oscillating contact with a SAE 52100 steel ball was reduced up to 70%. With lubrication a reduction up to 8 % with FVA no. 3 and up to 39 % with Selenia 5W40 respectively compared to a SAE52100 steel plate was measured.
The life time of the tribological system was increased uo to 350 times with the application of the coating on only one part of the tribological system.
The aim to create coating systems with a high wear resistance and excellent tribological properties was reached during the described period.
From the results of the oscillating ball on disc test 7 coating variants were tested on tappets in a valve train test at Schaeffler.
In the valve train test a reduction in friction up to 24 % was visible. The project target of friction reduction of 10 % can therefore be seen as reached. The well performing tappets showed a wear resistance that is maybe suitable for an application because in the valve train test wear of the coating was visible.
For the multilayer system H-Nanocoat 3 with a top layer of DLC an automatically working coating system was developed to produce this layer system without any problems on all the interfaces between substrate and layer system, as well as between the different layers in the coating system. It has been shown that hardness, layer structure and layer thickness can be tuned to the application. This technology is existing as part of a software package to control the production machine.
This coating layer is a coating based on a Cr adhesion layer and a subsequent nanostructured layer of W-C:H. This coating has high potential for impact and rolling wear resistance applications. Good results can be expected in roller bearings. First results are promising. These results have been confirmed by bench tests on roller bearings in Leeds, showing that this coating is extremely appropriate for rolling fatigue resistance. The optimum coating thickness appears to be in the range of 2,5 µm, Hardness values are tuneable
This coating system H-Nanocoat 2 is a coating layer which has high potential for abrasive wear resistance. The coating layer exists of a chromium adhesion layer, a W-C:H load carrying layer and a diamond-like carbon top layer. Good results can be expected in applications, where sliding wear is the major wear mechanism.. This is due to the hardness, as well as to the low cof. Promising wear results have been observed on initial tests on shims. Since in most applications sliding is one of the major wear mechanisms, this coating is expected to be useable in a wide range of applications as well. For the base layer potential coating modifcations have been developed that are expected to give good results in abrasicve wear by smoothening the surface roughness. For tuning the hardnesses of the different layers, the possibility exists to integrate Si as a doping element in the diamond-like carbon layer as well.
The developed Chromium+Carbon nanodispersion coating (Cr+C-ND) is a coating for protecting metallic surfaces from wear and to reduce the friction force under tribological loading. It is a nanostructured amorphous coating consisting of 80-95% carbon and 5-20% chromium. The nanostructure is based on nanometer-sized Cr and CrC inclusions in a mainly diamond-bonded amorphous carbon matrix. The overall coating hardness is high (30 GPa) resulting in good wear resistance. Compared to pure carbon films, the Cr+C-ND showes lower friction coefficients (0.08) under dry conditions in contact to steel.
The wear resistance in slightly lower compared to carbon films but the wear of counter part is significantly reduced. Both the crack resistance (fracture toughness) and the oxidation resistance of the Cr+C-ND are improved compared to carbon films. For these reasons the Cr+C-ND is predestined for tribological application under dry-running and mixed-lubrication conditions with emergeny-running conditions.
The coating can be deposited by vacuum-arc discharge in dedicated PVD coating machines. There was developed a pulsed arc technique allowing for high-rate deposition of good-quality Cr+C-ND in the thickness range 100 nm - 10 µm. The films can be deposited on complex three-dimensional metal substrates as steel components and tools. The nanostructuring is obtained by co-deposition from a graphite and a chromium arc source with highly activated plasmas. The films have high potential for low-wear and low-friction application e.g. on components in automotive industry. The special benefit of the coatings is the extremely low friction and wear under dry and mixed lubrication conditions.
Here we report on the protocol that INFM has developed for the characterization of tribological properties of coatings at the sub-micrometer scale using an atomic force microscope. This protocol is designed to provide quantitative results on corrugated samples, which is recognized as the most problematic issue in such measurements. The protocol developed by INFM is thus particularly interesting and adequate for the study of coatings provided by NANOCOAT partners. Results of first characterizations are shown. The major outlook of this work is the possibility of carrying on nano-tribological measurements on tribo-coatings in a liquid cell. This will allow to test the effect of different lubricants on the coatings.
An atomic force microscope (AFM) operated in the friction force mode (Friction Force Microscopy - FFM) is one of the most powerful techniques for the investigation of friction at the sub-micrometer scale. The slider in this case is represented by a micrometer-sized tip, with a radius of curvature from 10 to 100 nm. Friction and adhesion between such a small probe and a surface at this scale depend sensitively on the physico-chemical environment (lubricants, humidity, &) and local composition. It can be expected that any modification in the composition of a tribological coating, which affects the chemistry and structure at the submicrometer, down to the nanometer scale, as well as any change in the environmental conditions, will influence the nano-tribological behavior. In the optimization of performances of industry- and application-oriented tribological coatings, such as those developed in the framework of the NANOCOAT project, results of AFM/FFM characterization can therefore provide an additional and complementary feedback for the production of the coatings, when considered together with those of macroscopic testings.
In FFM topographic and friction maps of surfaces are acquired together. This is made possible by the simultaneous acquisition of the vertical and lateral deflections of the cantilever supporting the AFM tip. The formers are related to changes in the topographic relief, while the latter are proportional to the friction force between the tip and the sample surface. In order to perform quantitative nanofriction measurements, it is necessary to control and accurately measure both the magnitude and the direction of the forces acting on the AFM tip.
However, because of the local tilt of the surface, forces acting on the tip can be different from those inferred using the standard reference frame of the laboratory. In particular, the measured forces in the directions parallel and perpendicular to the AFM reference plane do not necessarily coincide with the forces acting parallel and perpendicular to the sample surface, which actually define the friction coefficient and the friction versus load characteristics of the interface under investigation. A topographic correction is thus required in order to obtain the value of the true friction coefficient.
We have developed a complete quantitative protocol for the characterization of the friction properties of corrugated surfaces using the AFM. The first part of the protocol consists in the simultaneous acquisition of topographic, applied loads, and lateral force maps. The local tilt of the surface is calculated from the topographic map. The external applied load is remotely controlled and synchronized with the end-line and end-frame triggers from the microscope. We can change the applied load after each scanned line during the acquisition of a single frame. A complete load ramp can be applied and recorded in a single AFM scan. The load range is typically 0 100 nN. The second part consists in the application of the topographic correction to experimental data, in order to extract the corrected values of the friction coefficient µ and the adhesive offset c.
We have applied the protocol to measure several coating produced by coater partners of Nanocoat. The results are published in the Nanocoat technical report.
We observed the smaller friction coefficient on the DLC samples from IWS. The biased DLC samples have smaller friction coefficient than the reference DLC.
Ns-carbon CrN from Microcoat have larger friction coefficient. Moreover, we noticed that on a 1 µm scale, the friction behavior of ns-carbon/CrN coatings is not uniform. Our analysis revealed the co-presence of several linear trends in the friction-load characteristics, corresponding to different friction coefficients (and adhesion). This can be due to non-homogeneity of the chemical composition of the coatings on the sub-micrometer scale, as well as to the presence of contaminants at the surface. The second stronger trend on ns-carbon/CrN coatings was observed mainly at higher loads (in parenthesis in the table; only the two strongest trends are reported).
The developed Carbon/Carbon multilayer (C/C-ML) is a coating for protecting metallic surfaces from wear and to reduce the friction force under tribological loading. It is a nanostructured amorphous coating consisting of 100% carbon. The layered nanostructure is obtained by periodic variation of chemical bonding state (sp-hybridization) between carbon atoms.
The film is composed of nanometre-layers with dominating sp3-content (diamond bonding) and dominating sp2-content (graphite bonding). Irrespective of partial graphite bonding the overall coating hardness is high (>40 GPa) resulting in extraordinary good wear resistance.
The nanolayering has two major benefits in comparison to not structured homogeneous coatings:
- Due to the nanolayering the intrinsic compressive film stress is reduced from 5-8 GPa to 1-3 GPa. As the compressive stress is a driving force for coating delamination, the nanostructured coatings show improved adhesion strength.
- Coating with an intrinsic nanostructure posses a higher resistance against crack propagation (=fracture toughness) due to energy dissipation on the tip of propagating cracks. For these two reasons the nanostructured C/C-ML is predestined for tribological application under demanding mechanical loading conditions.
The coating can be deposited by vacuum-arc discharge in dedicated PVD coating machines. There was developed a pulsed arc technique allowing for high-rate deposition of good-quality C/C-ML films in the thickness range 100 nm - 10 µm. The films can be deposited on complex three-dimensional metal substrates as steel components and tools.
The periodicity is obtained by periodical change of deposition parameters influencing the energy of depositing carbon species. The films have high potential for low-wear and low-friction application e.g. on components in automotive industry. The special benefit of the coatings is the extremely low friction and wear under dry and mixed lubrication conditions. First application tests in automotive industry revealed the high potential of these coating to obtain even super-low friction behaviour in the presence of adjusted lubrication oils.
The coating system H-Nanocoat 3 is a coating, based upon chromium nitride CrxNy. This coating is a very hard coating, containing a major part of Cr2N and can be used for abrasive and adhesive wear applications. Hardness values for this coating can be tuned and can go up to the range of 25 to 30 GPa. Due to the hardness the potential in abrasive wear application seems good.
The coating developed is a nanostructured carbon coating with no other doping elements and notably hydrogen free that showed more than twice the wear resistance of MoS2 and one third of the friction coefficient of TiN. The coating is obtained at a deposition temperature of 150°C, which makes it very interesting for temperature sensitive materials, like e.g. the 100Cr6 steel, of wide use in car engine valve train components. The technology for depositing the coating is a modification of the cathodic arc evaporation, a technique well known for its ability to produce high volume of parts at low cost. Future industrialisation of this coating, even to industrial sectors characterised by high production volumes and high cost effectiveness needs, seems therefore promising. The coating showed very good performances in a very demanding actual tribological application, namely the cam tappet interface in car engines. This tribological contact shows at the same time sliding, rolling, fatigue and lubrication effects.
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