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Self-mated magnesia stabilized zirconia (Mg-PSZ) ceramic sliding couples have been investigated at 100 N load (P0max= 1324 MPa) in oscillating sliding conditions in different humidity conditions in air and in hot steam. Temperatures have been varied up to 400 °C and pressures up to 6 bars. The results show that the wear behavior of MgO-ZrO2 under high Hertzian contact pressures is strongly dependent on temperature and is similar for both dry oscillating and oscillating in hot steam. However, although the evolution in wear rates on temperature is similar and the wear rates of MgO-ZrO2 plunged above 300 °C in hot steam and air by nearly three orders of magnitude, SEM micrographs revealed in hot steam at 400 °C smooth wear tracks. In contrast, hot steam enhanced the tribochemistry of self-mated alumina couples and reduced wear rates. Hot steam decreased the coefficients of friction of MgO-ZrO2 with increasing temperature, but not the wear rates.
The talk gives a historical introduction and introduces some of the biggest and most important research institutes in Germany dealing with tribology at Universities, scientific societies and companies. Some examples for research projects and focus areas are given. As an example for a research institute with a long history in tribological research the activities of BAM in Berlin are presented.
The aim of this research is to characterize a surface that has experienced low wear on asperities. The procedure used is similar to an Abbott-Firestone approach and based on functional bearing of projected area, surface area and material volume. Surface features extracted from surface height maps provide more comprehensive information about topography changes due to wear. Thus, they were used to detect low wear volumes on the top of asperities.
In this study the so-called laser-induced periodic surface structures (LIPSS, ripples) were produced on titanium alloy (Ti6Al4V) surfaces upon scan processing in air by a Ti:sapphire femtosecond (fs) laser. The tribological performance of the resulting surfaces was qualified in linear reciprocating sliding tribological tests (RSTT) against balls made of different materials (100Cr6 steel/Al2O3/Si3N4) using different oil-based lubricants. The admixture of the additive 2-ethylhexylzinc-dithiophosphate (ZDDP) to a base oil containing only anti-oxidants and temperature stabilizers disclosed the synergy of the additive with the laser-oxidized nanostructures. This interplay between the laser-textured sample topography and the local chemistry in the tribological contact area reduces friction and wear.
The cause and type of solid particle erosion varies across different industries and locations in plants, for instance the particles could be volcanic ash in aero-engines, fly ash in boilers, exfoliated scale in steam turbines or mineral matter in oil excavation. In all cases the durability of materials can be improved through better surface engineering and coatings, but the development of these is restricted also due to lack of generic models. In this respect, the simulation of a single impact with finite element methods using 100.000 knots would take about 15 minutes. In order to simulate an entire particle erosion experiment, up to one billion of such impacts would have to be considered. In order to simulate an entire particle erosion experiment, the current work presents an alternative approach capable of calculating about half a billion impacts on a substrate in less than six hours on a standard PC. The predictions of the simulation will be compared to a steel sample at 600°C eroded by aluminum oxide particles with a velocity around 210 m/s.
The performance of titanium alloy (Ti6Al4V) surfaces was investigated in lubricated reciprocating sliding tribological tests (RSTT). Special emphasis was laid on the effect of surface nanostructures in area of contact on the respective friction and wear behaviour. These so-called laser-induced periodic surface structures (LIPSS, ripples) were produced on the titanium alloy surface upon scan processing in air by an ultrashort pulsed femtosecond (fs) laser. As lubricant served two types of base oils, a pure polyalcylene-glycol, and an SAE 0W30 oil containing only antioxidants and temperature stabilizers. Tribological tests were carried out on polished as well as LIPSS covered areas using both types of base oil. A test metrics was established, combining the additive 2-ethylhexyl-zincdithiophosphate (ZDDP) or the ionic liquid [P6,6,6,14] [DEHP] (98% purity) with the respective base oils. The test metrics also considered the orientation of motion with respect to the orientation of the structures formed on the surface. Results are presented which show that the interplay between LIPSS and the local chemistry formed by the respective additives is beneficial for the tribological behaviour of the titanium alloy. Certain combinations of base oil, additive and LIPSS reduced friction and wear significantly in the tribological contact.
This lecture deals with the sliding behaviour of polymer materials in hydrogen environment. After a short introduction of the hydrogen activities at BAM, the tribological performances of polymer materials in gaseous hydrogen are presented and compared with air and vacuum environment. The second part focusses on the influence of the counterface materials in hydrogen. Finally, the last section is dedicated to experiments liquid hydrogen.
This lecture deals with the sliding behaviour of polymer composites in vacuum environment. At first, the effect of the polymer matrix and solid lubricants such as graphite and MoS2 are presented. The second part focusses on the influence of the residual pressure with experimental results obtained in high and ultrahigh vacuum.
The focus of this study is to evaluate of hydrogen on the friction and wear behavior of a wide range of polymer materials. Thereby, the tribological performance of filled and unfilled polymers from different suppliers were compared at room temperature in air and hydrogen gas (H2) as well as in liquid hydrogen at -253°C (LH2).
This lecture deals with the friction and wear of polymeric materials at cryogenic temperatures. The first part is dedicated to the low temperature properties of polymers and cryogenic environment as well as an introduction to cryotribology and friction models. The second part presents some experimental results, focusing on the effect of polymer composition, cryogenic media and stick-slip behaviour.
The tribological characteristics of pure and graphite filled polymers were investigated in gaseous hydrogen at ambient temperatures and in LH2 at -253°C. It could be shown that the tribological properties of PI and PEEK materials is related to the formation of a transfer film. The influence of both hydrogen and cryogenic temperatures will be discussed in the presentation.
The process window and range of functional properties of NbC is wide, because micro-hardness, hot hardness, sliding wear resistance, elastic modulus and toughness can be tailored by the C/Nb ratio, because Nb4C3, Nb6C5 and other short and long range ordered phases occur in the region of homogeneity of NbCx (0,75≤ x ≤1.0) in the binary Phase diagram, and by the type of binder. Further improvements enable the addition of secondary carbides. Supporting results from literature and different grades with varying C/Nb ratio or binder types were illuminated. Thus, the NbC system offers to producers a wider process window, than WC. The impact of these tailored properties on sliding wear and cutting performance was illuminated by tribological and machining results. NbC can be synthesized by carbothermal conversion of Nb2O5 or be metallurgically grown in melts and leached out as coarse NbC cubes. NbC provides comparably lower friction in many relevant tribo-contacts and displays low wear. NbC and Nb2O5 have so far no REACH classification related to human toxicology and are not listed as substances of very high concern contrary to WO3 and Co3O4.
Hydraulic oils are well established formulations developed around the pump test. Requirements for energy efficiency and also environmentally acceptable properties increased the demand for development. In the same time, system pressure and the used of servo-hydraulic vanes increased bringing specific formulations and materials to their limit.
The vane pump is a key component in hydraulic systems and many other tribosystems in hydraulic circuits operate under different tribological operating conditions. The concept for ranking of hydraulic oils consists in using existing SRV-based ASTM test methods for evaluation of friction, wear and extreme pressure properties: D6425, friction and wear of oils (homologue to DIN 51834-2), D7421, extreme pressure properties of oils and D7755, wear volumes of ball and disks (homologue to DIN 51834-3. The tribological properties are assessed under the regime of mixed/boundary lubrication The SRV-based concept of tribological profile generates the wear volumes on two triboelements (specimen) and the extreme pressure properties as well as the evolution of friction in the wear and extreme pressure load step test. Thus, the benchmark and validation of hydraulic oils bear on a wider range of tribological properties. Round robin test results using the aforementioned testing concept will be shown. Another outcome is tribological set limits for inclusion in hydrau¬lic oil speci¬fications.
Substituting tungsten carbide (WC) as cutting tools and for wear protection by niobium carbide (NbC)
(2016)
As a refractory carbide, niobium carbide (NbC) is today still a forgotten carbide with hidden properties, such as wear resistance, thus qualifying NbC for the group of tribological materials with enhanced wear resistance. Several phases, like Nb₄C₃, Nb₆C₅ and other short and long range ordered phases occur In the region of homogeneity of NbCx (0,75≤ x ≤1.0) in the binary phase diagram, which enable the tailoring of properties and offers a much wider process window than known from WC. The type binder (Co, Ni, NiMo) and its concentration as well as the sintering process (SPS, liquid phase sintering) determine the box “hardness-toughness”, which will be illuminated based on more than 100 grades.
The impact of these tailored properties on sliding wear (T= 22/400°C; v= 0,1-10 m/s) and cutting performance will be illuminated by tribological and machining results. Cutting test results under emulsion and coolant-free operation of cobalt and Fe3Al bonded, straight NbC versus WC based inserts against different alloys (C60, 100Cr6, 42CrMo4, X90CrMoV18, 300WA, GG35) will be highlighted.
Several phases, like Nb₄C₃, Nb₆C₅ and other short and long range ordered phases occur in the region of homogeneity of NbCₓ (0,75≤ x ≤1.0) in the binary phase diagram. Properties, like micro-hardness, hot hardness, sliding wear resistance, elastic modulus and toughness can be tailored by the C/Nb ratio, the addition of secondary carbides and the type of binder. Supporting results from different grades with varying C/Nb ratio or binder types were illuminated. Thus, the NbC system offers to producers a wider process window, than WC. The impact of These tailored properties on sliding wear and cutting performance was illuminated by tribological and machining results. Niobium is today largely available. NbC can be synthesized by carbothermal conversion of Nb₂O₅ or be metallurgically grown and leached out, provides comparably low friction in many relevant tribo-contacts and displays low wear. NbC and Nb₂O₅ have so far no REACH classification related to human toxicology and are not listed as substances of very high concern contrary to WO₃ and Co₃O₄.