Papers by Keyword: Low Friction

Abstract: Hydrogen technology can be one key for a transition to sustainable energy necessary to achieve climate targets and limit global warming to 1.5 °C since the beginning of the industrial revolution. Hydrogen as a CO₂ neutral energy carrier must replace fossil fuels from the existing natural gas grid and infrastructure to enable an environmentally friendly and circular economy in future societies. Batteries and e-fuels are practicable technologies for short term and quantitatively limited energy provision, with disadvantages including raw material demands and technologically complex transformation cycles. Utilizing advanced power-to-gas concepts, hydrogen will not only be most efficient technology in energy storage, but also allows adaption and reuse of existing energy transportation infrastructure.To provide volatile hydrogen gas in the required flow and energy densities, advanced compression technology needs to be developed inspired by conventional gas compression systems. Reciprocating piston compressors are developed for high-pressure hydrogen applications, providing high pressure levels and flow rates. Compression equipment must be designed for non-lubricated dry-running conditions, as high gas purity standards of hydrogen do not allow for oil-based lubricants to be introduced into the process gas. High-strength carbon fiber reinforced composites are developed as piston and packing ring materials to withstand extreme pressure differences under harsh thermo-mechanically loaded operation conditions.Promising candidates with high strength and wear resistance in the form of PPS-polymers, are developed with PTFE solid lubricants and different carbon fiber fractions to combine high strength, with low friction and wear, improve pressure operation range, and limit down times of hydrogen piston compressors. The current work describes tribological testing of advanced PPS-polymers with 10 to 30 wt.% carbon fibers in a high-velocity tribometer under hydrogen gas atmosphere. Supporting thermo-mechanical tests give new insights in deformation mechanisms of fiber reinforced polymer composites and allow conclusions on their applicability for hydrogen compression.

Abstract: Nanostructured smart coatings (NSC) based on the TiAlSi-CN composite structure elements were deposited using reactive high-power physical vapor deposition (PVD) technique. The advanced modular deposition system included up to 8 high-power magnetron sputtering devices (MSD) allowing operate them simultaneously and exceed power density of 120 W/cm² within each device erosion zone. The novel designed NSC on bearing steel 100Cr6 substrates demonstrated enhanced mechanical and tribological properties comparably with bearing steel ones required for multifunctional high-tech applications. The deposited NSC containing TiAlSi-CN nanoparticles strengthened by elemental additives Cr and Nb exhibited microhardness as high as 2500 HV values in comparison with 750 HV of 100Cr6 steel substrates. Load-displacement curves obey Meyer’s power-law surprisingly well because power-trendline fitted ones by R-squared value of 0.9999 for all the film-samples. Tribological properties were measured under dry friction conditions between the bearing steel ball of Ø 6 mm and the film-samples’ flat surface. Coefficient of friction (CoF) ranges between 0.22-0.56 depending on a sample and load. Tribotracks worn under the friction indenter were too shallow to evaluate them by Mitutoyo profilometer SJ-500. Therefore, the wear rate was estimated as ball wear of the friction indenter.

Abstract: Careful consideration of friction and wear could save the U.S. economy as much as $120 billion per year. Friction, wear, and lubrication have direct influence on the performance, reliability, and service life of a device that contains moving components. These components are found in applications of energy conversion, power generation, energy harvesting in the broader fields such as agriculture, transportation, and bioengineering etc. The useful life of these systems and their energy efficiency can further be improved by improving the surface performances of sliding systems. Ceramics matrix multifunctional composite due to their unique properties are one of the alternatives for these applications. We report development of alumina based ceramic matrix composites (CMCs) with in-situ functional phases. The overview of properties will be provided. The mechanism for low friction will be discussed. In this investigation, the reinforcement (boron) addition showed strong influence on the in-situ phase formation and surface performance. The phase characterization confirmed formation of AlB₂, B₂O₃, and Al₁₈B₄O₃₃. The sintering temperature showed influence on the stability of these phases. The mixed mode failure was evident from the wear tests. It was found that the coefficient of friction was reduced up to 30% when compared to parent alumina. These newly designed multifunctional composites potential candidate materials that improve the energy efficiency and sustainability.

Abstract: Gel is a fascinating material for its unique properties, such as phase-transition, chemomechanical behavior, stimuli-responsiveness, low surface sliding friction, and for its possible wide application in many industry fields. Recently, hydrogels have drawn special attraction in biological field due to its possible applications as soft man-made tissues. However, conventional hydrogels, especially polyelectrolyte gels, are mechanically too weak to be practically used in any stress or strain bearing applications. Inspired by the structure of articular cartilage, we discovered a general method to obtain very strong polyelectrolyte hydrogels containing 60-90% water by inducing a double-network (DN) structure for various combinations of hydrophilic polymers. The soft and wet gel materials with both a high strength and an extremely low surface friction would find wide applications not only in industry but also in biomedical field, for example, as substitutes of articular cartilage or other bio-tissues.

Abstract: The paper presents the experimental results on an aluminum alloy and a silver alloy processed by equal channel angular extrusion in order to refine the grains. Two type of extrusion dies have been used for experimental works: one with fixed walls and the other one with movable walls in order to reduce the friction during extrusion process. The new concept of the die consists in simultaneously pressing of two samples in one entering channel with two opposite exit channels. The channel geometry, friction contact, strain rate, extrusion load and micro structure aspects are presented.

Abstract: Ceramic carbon based coatings have become common on tools and machine components, mainly because they offer a greatly reduced friction, as compared to uncoated steel contacts, in combination with a considerable wear protection. Very often they contain alloying elements such as different metals to control properties like hardness, wear resistance and lubricity. Applied to component surfaces, also properties relating to the running-in behaviour become important since an efficient running-in is crucial for their long term steady-state functionality. Also, even though component coatings are meant to provide low friction in dry sliding, they are increasingly used also in lubricated situations. This raises demands for compatibility with common lubricants. All these aspects have to be considered when developing new tribological coatings and some of these are addressed in this work. Results from different sliding tests with coated and uncoated surfaces in both dry and boundary lubricated contacts are presented. The generated tribofilms and their influence on the tribological properties are compared for the different sliding conditions. It is also shown how lubricants and their additives can affect the running-in, the tribofilm formation, and alter the steady state friction.

Abstract: TiC/a-C:H nanocomposite coatings have been deposited by magnetron sputtering and are composed of 2-5nm TiC nanocrystallites well separated by amorphous hydrocarbon (a-C:H) of about 2nm separation width. A transition from columnar to glassy microstructure has been observed with increasing substrate bias or carbon content. Micro-cracks induced by nanoindentation or wear tests readily propagate through the column boundaries whereas the coatings without a columnar microstructure show supertough behavior. The nanocomposite coatings exhibit hardness of 5~20 GPa, superior wear resistance and strong self-lubrication effects with a friction coefficient of 0.05 in air and 0.01 in nitrogen under dry sliding against uncoated bearing steel balls. Especially, the transitions from low to ultralow friction or the reverse are repeatedly switchable if the atmosphere is cycled between ambient air and nitrogen. The lowest wear rate is obtained at high humidity.