ICMCTF2016 Session B3-1: Deposition Technologies and Applications for Diamond-like Coatings

Thursday, April 28, 2016 1:30 PM in Room Golden West

Thursday Afternoon

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1:30 PM B3-1-1 Amorphous Carbon, DLC, and Carbon Based Nanostructured Composite Coatings - a Resume of Selected Thin Film Design and Process Approaches Towards High Performance Applications
Michael Stueber (Karlsruhe Institute of Technology (KIT), Germany)
Amorphous carbon and diamond like carbon coatings have reached high quality standards and are widely used in various industries today. However, increasing demands for superior functionalities in high performance applications require continuous improvement and development of both thin films design and properties and related deposition techniques. Apart from the enormous achievements made on amorphous carbon and DLC coatings huge know-how and expertise has been collected on a new class of thin film materials, named carbon-based nanostructured composites. In a simple design, these materials are two-phase composites built of a nanocrystalline transition metal carbide and an amorphous carbon phase. Depending on their microstructural design (i.e. volume fractions of the phases, constitution and grain size of the carbide phase, nature of the carbon phase) these novel materials exhibit interesting multifunctional properties, making them promising candidates for applications. Yet, these materials have been considered for and tested in selective technical environments only. This presentation will briefly address the latest state-of-the-art and newest developments in the field of amorphous carbon and DLC films, with a focus on wear applications. It will then review major developments made in the past decade on wear resistant, low friction carbon based nanostructured composite coatings. Fundamental materials science issues as well as thin film design concepts, tribological performances, deposition techniques and scale-up measures will be discussed. Substantial data will be presented on basis of the most prominent coating system TiC/a-C that has gained large interest in the R&D laboratories. Finally, the by now not yet explored potential for the development and synthesis of new tailor-made coatings for many applications, covering mechanical engineering (i.e. wear protective, environmentally friendly materials), energy technologies (i.e. thin film solar cells or batteries), electronics and optics, and biophysics and life sciences, will be demonstrated.
2:10 PM B3-1-3 Improvement of the Properties and the Adherence of the DLC Coatings Deposited using a Modified Pulsed-DC PECVD Technique and an Additional Cathode
Gil Capote (Universidad Nacional de Colombia, Colombia); Marco Ramírez, VladimirJesus Trava-Airoldi (INPE, Brazil)

Diamond-like carbon (DLC) coatings have attracted significant attention due to their low friction, high hardness, high elastic modulus, chemical inertness, biocompatibility, and high wear resistance. These coatings have been grown using different deposition methods and hydrocarbon precursors in order to find the best set of mechanical and tribological proprieties. The major disadvantage of hard DLC coatings deposition and, therefore, their technical applications is that there is often a relatively low adhesion on metallic substrates caused by very high total compressive stress on these coatings.

In this work, deposition of hard and adherent DLC coatings employing an asymmetrical bipolar pulsed-DC PECVD system and an active screen that worked as an additional cathode is presented. This system represented a step forward for thin coating growth by using very lower pressure (about 0.1 Pa) in collision less regime and higher plasma density than the conventional PECVD system. Acetylene gas was used as a precursor. In order to overcome the high residual stress and low adherence of DLC coatings on steel substrates, a thin amorphous silicon interlayer was deposited as an interface. The interlayer was synthesized using silane as precursor gas and varying the applied self-bias voltage during deposition.

The DLC coatings were analyzed according to their microstructural, mechanical, and tribological properties as a function of the substrate bias voltage. The film's atomic arrangements and the hydrogen content of the films were estimated by means of Raman spectroscopy. The total stress was evaluated through the measurement of the substrate curvature, using a profilometer, while nanoindentation experiments helped determine the films' hardness and elastic modulus. The friction coefficient and the wear rates of the films were determined using a tribometer in unlubricated sliding friction experiments, while the critical load of failure was determined by a classical scratch test.

The results showed that the use of the modified experimental setup and an amorphous silicon interlayer improved the DLC films' deposition onto steel substrates, producing good adhesion, low compressive stress, and a high hardness. The composition, microstructure, and mechanical and tribological properties of the films were dependent on the applied bias voltage. These results suggest that a combination of a modified pulsed-DC PECVD system, the use of an active screen as an additional cathode, and acetylene as a precursor gas for growing DLC films may represent a new and useful alternative for mechanical and tribological applications.

2:30 PM B3-1-4 Synthesis of DLC Coatings by HPPMS using Ar, Ne and He as Process Gases
Kirsten Bobzin, Tobias Brögelmann, Christian Kalscheuer, Martin Engels (RWTH Aachen University, Germany)

Diamond-like carbon (DLC) coatings are used in numerous tribological applications, for example components of the automotive powertrain. The hardness of these coatings contributes to the reduction of the component wear and correlates with the sp3/sp2 bond ratio between the carbon atoms, where sp3 bonds are similar to the diamond structure. Physical vapor deposition (PVD) processes like pulsed laser deposition (PLD) or filtered cathodic arc (FCA) have been used for the deposition of DLC coatings with high sp3/sp2 ratios, so far. However, coatings deposited by PLD or FCA exhibit high defect densities and surface roughnesses. Therefore, research is upon the high power pulsed/impulse magnetron sputtering (HPPMS/HiPIMS), which in contrast to mentioned processes provides smooth coatings and therefore less post processing. Synthesizing DLC coatings with a high sp3/sp2 ratio requires high energetic carbon ions, whose generations strongly depend on the HPPMS process parameters. The synthesis of hard DLC coatings by means of HPPMS, especially with different process gases has been reported in few works, yet. Plasma diagnostics have shown that the energy of the carbon ions in the plasma strongly depends on the process gas mixture, the process gas pressure and the bias voltage. An increased fraction of high energetic carbon ions in the HPPMS plasma has been reported for process gases with a higher ionization energy as well as for higher bias voltage and lower process gas pressure. Therefore, the aim of this work is to investigate the correlation of the plasma parameters with the properties of DLC coatings. Ar, Ne and He were used as process gases. Process gas pressure and bias voltage were varied between p = 0.5 – 2.0 Pa and UB = -300 – 0 V, respectively. The coatings were deposited in a high volume semi-industrial coating unit. The coating properties were analyzed by means of nanoindentation, Raman spectroscopy, scanning electron microscopy and confocal laserscanning microscopy. It was observed that the coating properties strongly correlate with the results from the plasma diagnostics. Dependencies of the sp3/sp2 ratios and hardness could be found for increasing ionization energy of the process gas. Furthermore, an influence of the process gas pressure and bias voltages could be observed. Hardness values up to HU = 45 GPa have been achieved. In conclusion it can be claimed that synthesis of DLC coatings with high hardness is possible by HPPMS processes using process gas mixtures of Ar, Ne and He.

2:50 PM B3-1-5 Design and Industrial Applications of Functionalized DLC Coatings
Sébastien Guimond (Oerlikon Balzers, Oerlikon Surface Solutions AG, Liechtenstein); Etienne Billot (Oerlikon Balzers, Oerlikon Balzers Coating Germany GmbH, Germany); Frédéric Meunier (Oerlikon Balzers, Oerlikon Balzers, France); Olivier Jarry (Oerlikon Balzers, Oerlikon Balzers Coating Germany GmbH, Germany)
a-C:H diamond like carbon (DLC) coatings are widely applied to reduce wear and friction of various components. Additionally to these beneficial mechanical properties, numerous applications also have specific optical, electrical or chemical coating requirements. For instance, scratch and abrasion-resistant DLC coatings having a darker color are demanded for functional decorative parts. Tools used for plastic molding require DLC films providing wear resistance, but also good corrosion protection and an excellent release of the molded parts. To achieve these combinations of properties, a-C:H films are modified by either modulating the conditions during deposition or by using dopants.
3:10 PM B3-1-6 Deposition of Si-Containing DLC by using Ultra-High Speed PECVD Employing Surface Wave Propagation of 2.45-GHz Microwaves
Hiroyuki Kousaka (Nagoya University, Japan)
Recently, with increasing demands for energy saving by friction reduction and lifetime extension by wear reduction, the application of DLC (Diamond-Like Carbon) is spreading gradually and steadily. Plasma CVD is one of the promising manufacturing methods of DLC due to its excellent capability for coating 3-dimensional shapes; however, its coating speed is typically not so high, ~1 μm/h due to the use of low-density (ne~108−1010 cm−3) DC or RF plasma. For further increase of the coating speed, we have proposed an ultra-high-speed DLC coating at over 100 μm/h employing much higher-density plasma (ne~1011−1013 cm−3), which is sustained by microwave propagation along plasma-sheath interface. In this work, we investigated the effect of atomic composition of DLC film on the deposition rate and hardness in such ultra-high-speed DLC coating. Si-containing a-C:H films (one type of DLC) were deposited on steel substrates by different 2 methods: DC plasma and microwave-excited high-density near plasma, or our newly proposed method, where the gas composition of Ar, CH4, C2H2, and TMS, and the duty ratio of microwave and substrate bias were changed. Note that the substrate bias was fixed to be −500 V. For example, under the same condition except microwave injection, the deposition rate and hardness of the DLC deposited by DC plasma were 2.5 μm/h and 11.8 GPa, respectively; while the deposition rate and hardness of the DLC deposited by microwave-excited high-density near plasma were 156 μm/h and 20.8 GPa, respectively. The atomic composition of the films was evaluated by XPS for C, O, and Si, and RBS-ERDA for H/C ratio. Within the range of our results, the hardness films were almost linearly decreased from 6 to 22 GPa with decreasing hydrogen content from 45% to 22%, being independent from the composition of C and Si.
3:30 PM B3-1-7 The Effect of Substrate Bias Voltage on Mechanical and Tribological Properties of Sputter-deposited Hydrogen-free Amorphous Carbon Coatings
Chang Liu, Allan Matthews, Adrian Leyland (The University of Sheffield, UK)
Hydrogen-free amorphous carbon coatings were deposited on to AISI 316 stainless steel substrates by magnetron sputtering of a graphite target under different pulsed substrate negative bias voltages (-50V, -90V, -130V, -170V and -210V) with frequency of 250KHz and duty cycle of 30%. The microstructure and mechanical properties of such coatings were investigated by Raman spectroscopy, scanning electron microscopy, transmission electron microscopy and nano-indentation. Scratch adhesion and pin-on-disc sliding wear tests were also employed for tribological performance evaluation. The results show that all coatings possess high H/E ratios around 0.12, while hardness and elastic modulus increase with substrate negative bias from -50V to -130V, and then decrease with further increasing bias voltage, up to -210V. Coating adhesion and sliding wear properties are closely related to the substrate bias voltage. It appears that a bias of -90V provides the optimum coating properties to obtain good tribological performance.
3:50 PM B3-1-8 The Fullerene Structure Control of Diamond-like Carbon Films with Super Low Friction
Junyan Zhang (State Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, China)

The fullerene-like nanostructure hydrogenated carbon films exhibited high hardness and ultra-high elasticity though having high sp2 hybrid carbon bonds, which implies that the hardness of carbon films is not only related to the content of sp3 hybrid carbon bonds, but also contributed by the microstructure. The reason is due to the curvature structure of fullerene like structure, which extends the strength of graphite plane hexagon into three dimension space network, in turn, increasing the hardness and elasticity of carbon films. More importantly, the films demonstrated super low friction in air, meaning low friction solid lubricant with practical application value. With five- and seven-member ring as the representative of fullerene like structure, the fullerene like structure of the carbon films could be adjusted via the hydrogen content in the deposition gas sources. It was found that there is direct relationship between the fullerene like structure and the friction coefficient, the more fullerene like structure, the lower friction coefficient of the carbon film, indicating that the fullerene like structure could govern the friction behavior of the carbon film. During the sliding process, the friction induced more fullerene like structure generated at the frictional interface, accounting for ultra low friction. Some applications of the fullerene like structure carbon films with super low friction are carried out to engine parts such as high pressure common rail fuel system to save energy and reduce emission. The results will expand and ensure the application of carbon films to most frictional parts of engine, and thus to save fuel and reduce emission much more.

[1] Qi Wang, Chengbing Wang, Zhou Wang, Junyan Zhang*, Deyan He, Applied Physics Letters, 2007, 91(14), pp141902,

[2] Yongfu Wang, Junmeng Guo, Kaixiong Gao, Bin Zhang, Aimin Liang, Junyan Zhang*, Carbon, 2014,77, pp518

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