In the current era of green energy adoption for reaching the zero-carbon target, the mobility sector is extensively working together to use hydrogen as a major source of energy, especially in vehicles with long range requirements. For this, Proton Exchange Membrane Fuel Cells (PEMFC) are employed to convert the chemical energy of hydrogen back into electricity. Acceptability of PEMFC in the automotive field mostly depends on system efficiency, durability & cost of the FC stack. In PEMFC, the bipolar plate (BPP) is a critical component of the system, which realizes the transport of gases to the electrodes, evacuates reactant product water and ensures electrical current collection. In some applications, graphite is used as material for bipolar plates due to good chemical stability and corrosion resistance, whereas it is also a rather brittle material with some manufacturing challenges. In mobile applications, metallic bipolar plates are widely used, as they allow for a significantly higher power density of the stack and have good mechanical strength & electric conductivity. Metallic bipolar plates usually feature a protective coating to improve the durability of the system. In this paper, the role of bipolar plates is discussed, and different coating materials are evaluated for performance & cost. An in-house testing strategy is defined to validate coated metallic bipolar plates, which are tested under various operating conditions. Subsequently, test results are discussed to check the improvement of using noble metal free material over available PGM (Platinum Group Metal) coating materials.

Purpose The curved and tribologically highly stressed surfaces of bearing components pose a major challenge for steel alloys or tribological resistant coatings like tetrahedral amorphous carbon (ta-C) coatings which in particular have an increased risk of delamination due to the significantly increased residual stresses. A possibility to prevent coating failure is the use of dopants while maintaining or even increasing tribological properties. This study aims to compare the tribological behavior of several doped diamond-like-carbon coatings with an undoped ta-C coating under varying slip conditions and Hertzian pressure up to 1800 MPa. Design/methodology/approach For this purpose, the tribological behavior was studied using of a ball-on-disc tribometer and a two-disc test rig under mixed/boundary conditions. The tests were conducted with coated specimens against uncoated 100Cr6 steel. Additionally, the influence of lubrication additives was studied due to the use of two fully formulated PAO-based oils, one without and one with molybdenum containing additives. The friction was measured in situ , and the wear was analyzed trough laser scanning microscopy and tactile measurement. Findings It was shown that the use of doped ta-C coatings exhibited a tendency for a more favorable tribological behavior compared to undoped ta-C coatings, with no general dependence on the lubricants used. The use of the most suitable coatings reduced the wear of the steel counter-body considerably. Originality/value To the best of the authors’ knowledge, this is the first approach of testing the tribological behavior of these doped ta-C coatings, developed for friction efficiency, in dependency on lubrication additives under the given load collective. The approach is relevant to determine whether the friction reduction and the wear inhibition of these coatings are suitable for higher contact pressures and load cycles. Peer review The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-11-2022-0336/

Friction and wear are responsible for approximately one-fourth of the global energy losses. According to Holmberg et al., these losses correspond to 119 EJ of the world’s total energy consumption from tribological contacts, based on the main sectors: transportation, manufacturing, power generation and residential. In this case, 20% (103 EJ) is used to overcome friction and 3% (16 EJ) is used to re-manufacture worn parts due to wear-related issues. These global energy losses have a huge impact on economic and ecological aspects. Figure 1 summarizes the impact of friction and wear on energy consumption, generated costs and CO2 emissions.

Due to growing environmental concerns and legislative requirements it is more and more important to reduce friction in highly stressed contacts of combustion engines to reduce engine out emissions and to improve fuel efficiency. Picture 1 shows exemplary friction losses in internal combustion engines with bucket tappet valve train as a function of engine speed. The valve train system has a significant part of the power train function and is a major contributor to frictional losses.

The energy efficiency in internal combustion engines is a key factor for the reduction of CO 2 -emissions of passenger cars and commercial vehicles. Diamond-like carbon (DLC) coatings in highly stressed engine components are therefore widely used for friction reduction and wear protection. One application is the valve train of the combustion engine due to its considerable frictional losses especially under boundary and mixed friction conditions at lower crankshaft speeds. In this regard, the tribological contact bucket tappet/camshaft in the valve train offers high potential for friction reduction but places also high demands on DLC coatings due to its complex kinematics and different contact pressures depending on the cam contours and the camshaft angle and speed. The aim of this work was to analyze the influence of the contact pressure on ultra-low friction behavior within the sliding contact ball-on-disc. This tribological contact was analyzed in a pin-on-disc tribometer using series-production DLC coated tappets (16MnCr5, AISI 5115) and steel balls (100Cr6, AISI 52100) ensuring same material pairing as in the real application. A synthetic oil PAO (polyalphaolefine) formulated with the friction modifier additive glycerol mono-oleat (GMO) was used for the tribometer tests. The influence of the contact pressure on the ultra-low friction behavior was tested as a function of the surface roughness under room temperature conditions (20 ± 1 °C) and a sliding velocity of 0,1 m/s. The wear of the superhard DLC coated functional surfaces was analyzed by means of confocal laser scanning microscopy (CLSM). The findings were correlated with the frictional behavior observed in the pin-on-disc tribometer. The results with friction coefficients lower than 0.02 and no visible wear reveal potential of DLC coating systems for energy efficiency as major enabler for the Mobility for Tomorrow.

Amorphous carbon coatings are more and more used in combustion engines. In the valve train these coatings are applied in order to fulfill legislative guidelines concerning energy efficiency and CO2 emissions. Up to now the effect of interactions between additives and such coatings on the friction is not sufficiently understood. Especially the high complexity of valve train systems and large experimental effort needed for a coating development show the need for a specific prediction of the friction behavior. Since an analytical prediction in such complex systems is not possible, always empirical studies are needed to determine the tribological behavior. This article presents the development and optimization of different multilayer artificial neural networks (ANNs) to predict the friction behavior on basis of tribological test data. For this a multitude of experiments were carried out by using various tribological test equipments whereby input parameters like type of coating, base oil, additives, temperature, pressure, etc. were varied systematically. The predictive capabilities of the ANN models were validated with experimental results. With a systematic variation of the learning rate and structure of the ANNs, a correlation coefficient from 0.69 up to 0.85 and relative absolute error of about 13% to 21 % could be achieved.

Modern components and systems for automotive and industrial applications have to meet various requirements in multiple technical fields. Apart from properties that affect the part itself like geometry, stiffness, weight or rigidity the surface properties must be adjusted to the growing environmental requirements. Therefore coatings are increasingly applied to reduce the friction losses of car components, improve fuel efficiency and reduce CO2-emissions. This article describes how to use surface technology as a modern design element for components and systems to enable the demanding requirements on market leading automotive and industrial products. Therefore Schaeffler has developed and established a coating tool box for customized surfaces to deliver the right solutions for all that needs and requests with the corresponding coating system enabled by PVD-/ PACVD-, spraying or electrochemical technology. For innovative products it is extremely important that coatings are considered as design elements and integrated in the product development process at a very early stage. In this article tribological coatings are viewed within a holistic and design-oriented context. The latest developments of amorphous carbon coatings, their characteristics as well as the technical and economical effects of their use in combustion engines and industrial bearing applications are described. The presented Triondur (R) amorphous carbon based coating systems (a-C:H; a-C:H:Me; a-C:H:X and ta-C) are excellent examples for customized tribological systems like bucket tappets or roller bearings. Triondur (R) carbon coatings offer the following advantages: super low friction with highest wear resistance, customized surface energy, optimized wetability and interaction with formulated engine oils and low adhesion to the counterpart.