The objective of the research work was to study the potential of commercial ceramics such as Al
2O
3, Al
2O
3–ZrO
2 and SiC in pairing with steel 100Cr6 and laser-assisted deterministic ...microtexturing of the flat functional surfaces as design element for fast running friction systems, such as multiple disc clutches, under unidirectional oil lubricated sliding. A more fundamental part of the study was oriented towards understanding of the effect of microtexturing on mechanisms at mixed or boundary lubrication and development of lubricating oil film in the contact area. Experiments were carried out with pellet/disc geometry at relatively low velocities ≤0.3
m/s and normal loads ≤10
N using a model test with an attached microscope for in situ observation of the contact area. In the second part, friction behaviour of the different ceramic materials with and without microtexturing was characterised using a friction test rig at sliding velocities up to 10
m/s and normal loads ≤60
N under more practical-oriented conditions. Results showed that frictional behaviour was significantly influenced by the ceramic material and features of microtexturing, e.g. dimples, channels, width, depth and area coverage fraction. Improved understanding of operating mechanisms and design rules of microtexturing for controlling friction coefficient at practical sliding systems was obtained from a descriptive model.
Tribological properties of a system are very important for saving energy or increasing service life as in automotive industry. It is known that wear and friction behaviour is strongly influenced by ...the topography of the mated surfaces. In case of lubricated sliding contact the tribological properties can be improved by generating a defined surface structure in form of small channels or isolated pits. Depending on the structure it may act as a reservoir for the lubricant and hampers the drain of the lubricant. In addition, wear particles can be removed from the contact area and can be collected inside the structures.
In the present paper, a Nd:YAG-laser was used to generate different structures on ceramic (Al
2O
3) and steel (100Cr6) surfaces. Microchannels and micropits were generated onto an otherwise flat surface by a laser ablation process. Due to the high flexibility of the laser system, structural features such as size, density and orientation could be varied easily by changing the laser parameters. The effects of different topographies on friction and wear behaviour were examined using a cylinder/plate tribometer for lubricated and reversed sliding contact.
Laser structured 100Cr6 and alumina surfaces mated to 100Cr6 cylinders showed that a reduction of friction could be achieved in comparison to the polished surfaces. Dependent on the kind of the surface structure the coefficient of friction could be reduced up to 30%, especially in the initial period of the tribological experiment. The results show that the laser technique is an effective tool to optimise the topography of tribological surfaces.
Li–Co–O thin film cathodes have been deposited onto Si and stainless steel substrates by RF magnetron sputtering from a ceramic LiCoO
2 target at various working gas pressures from 0.15 to 25
Pa. ...Composition, crystal structure and thin film morphology were examined and properties such as intrinsic stress, conductivity and film density were determined. As-deposited films at 0.15
Pa as well as in the range between 5
Pa and 10
Pa working gas pressure showed a nanocrystalline metastable rocksalt structure with disordered cation arrangement and were nearly stoichiometric. To induce a cation ordering the films were annealed in a furnace at temperatures between 100 and 600
°C for 3
h in argon/oxygen atmosphere (Ar:O
2
=
4.5:5) of 10
Pa. This cation ordering process was observed by XRD and Raman spectroscopy. For the films deposited at 10
Pa gas pressure an annealing temperature of 600
°C leads to the formation of the high temperature phase HT-LiCoO
2 with a layered structure. The Raman spectrum of the films deposited at 0.15
Pa and annealed at 400
°C indicates the formation of the low temperature phase LT-LiCoO
2 with a cubic spinel-related structure, which is assumed to be stabilized due to high compressive stress in the film. The electrochemical characterisation of annealed thin film cathodes revealed that the discharge capacity strongly depends on the crystal structure. Thin Li–Co–O films with a perfect layered HT-LiCoO
2 structure showed the highest discharge capacities.
Surface engineering was carried out on oxide ceramics (Al
2O
3–ZrO
2, ZrO
2) using two different laser-assisted processes: (i) modification of the edge layer of the ceramic by laser induced remelting ...and alloying and/or (ii) surface microtexturing by laser ablation. Crossed microchannels and elongated microdimples oriented parallel to each other were chosen as texture patterns and produced on flat specimens of the ceramics. Effects of these surface treatments on the tribological performance of steel/ceramic and ceramic/ceramic pairs were studied during reciprocating sliding in distilled water using a pellet-on-plate-geometry.
The results showed a substantial reduction in friction and wear depending on the materials mated and the texture pattern used. With others, the running-in behaviour with high values of the friction coefficient of the sliding pairs could be considerably improved.
Surface properties of single-crystalline and polycrystalline silicon carbide (SiC) specimens were measured using atomic force/friction force microscopy, Auger electron spectroscopy and ...nano-indentation techniques. Running-in behavior during sliding tests in vacuum was studied on self-mated SiC pairs as a function of surface quality produced by machining. Tribological mechanisms were analyzed in short-time tests using a high-resolution micro-tribometer and then were related to results obtained from macro-tribological tests in humid air and in the presence of distilled water. Information on the structure, chemical composition and properties of SiC surfaces resulting from measurements on the nanoscale can be very useful for explaining tribological performance under far different operating conditions such as in vacuum or air, with contact areas ranging from diameters of a few nanometers to one millimeter and initial applied contact pressure from about 1MPa to 3GPa. Friction and wear mechanisms are discussed as functions of surface composition and roughness, vacuum and humidity of air.
Increasing requirements for friction systems such as smaller dimensions and greater power transmission lead to enhanced power density in dry frictional contact. Present organic based materials will ...be overloaded due to severe conditions and new friction materials are needed maybe on the basis of advanced ceramics. In the present study, ceramic composites were produced by embedding TiN particles into the surface of a commercial monolithic Al2O3 ceramic using a laser-assisted process. In this way multiphase microstructures were achieved in a surface layer of about 300 mm thickness. Tribological performance of the ceramic composites was studied in a pellet-on-disc tribometer by running consecutive short-time tests as function of the counterbody material, sliding speed, humidity and temperature. The results showed a substantially improved stability of friction coefficient compared with the monolithic alumina used for reference.
Tribological tests were conducted on different pairs of the bearing steel 100Cr6 and a commercial alumina under unlubricated and oil lubricated conditions where the transition behaviour from static ...to kinetic friction as a function of surface finish and contact pressure was of particular interest. Static and kinetic friction were measured using a laboratory tribometer with ball-on-plate geometry at an extremely low tangential speed of 8.3
μm/s applied to the plate specimen. Results showed a significant effect of surface finish on both the static and kinetic coefficients of friction as well as on the transition behaviour. Transition behaviour was strongly dependent on the materials mated. The self-mated steel pairs showed greater values of kinetic than static coefficient of friction while no significant difference of both friction values was measured on self-mated alumina pairs with ground plate specimens. Influence of oil lubrication on static friction was small compared with that on kinetic friction where the last one was substantially reduced by oil lubrication with 100Cr6/100Cr6 and 100Cr6/Al
2O
3 pairs, particularly. Stick-slip effects occurred with both unlubricated and lubricated pairs under high normal loads and depending on surface finish.
Large-scale production of ceramic and metallic micro components via micro powder injection moulding (μPIM) of filled feedstocks with abrasive particles requires mould inserts with a high wear ...resistance. Therefore, the wear behaviour of unalloyed, low- and high-alloyed steels, electroplated nickel and brass CuZn37 was studied using a specially developed laboratory tribometer simulating powder injection moulding with zirconia, alumina and steel feedstocks. Highest wear resistance was measured for the high-alloyed steel X175VCrMo9-5 which was produced by a powder metallurgy process. This steel was characterized by a homogeneous microstructure with a martensitic matrix and about 20
vol% fine carbides. In tests with ceramic feedstock the wear resistance of single-phase electroplated nickel was significantly higher than that of the heat-treated tool steels 30CrMo6 and X38CrMoV5-1 of higher hardness. These results indicate that in micro powder injection moulding wear behaviour can depend more on microstructural parameters like homogeneity than on hardness of the materials. The wear behaviour also was strongly influenced by the characteristics of the feedstock (e.g. amount, size, shape and hardness of ceramic or metallic particles).
Manufacturing of ceramic and metallic micro components in micro powder injection moulding (μPIM) requires mould inserts offering high wear resistance and a sufficient demoulding behaviour. Within the ...frame of this research μPIM mould inserts made from low and high alloyed tool steel were structured by micro milling and finished by micro peening and ultrasonic wet peening. Influence of surface condition on wear and demoulding behaviour of the steels in μPIM with ceramic feedstock was characterized using a laboratory tribotester simulating powder injection moulding and a specially adapted static friction tester. Results indicate that performance of mould inserts in micro powder injection moulding depends not only on hardness, surface condition and homogeneity of the mould insert materials but also is strongly influenced by the characteristics of the feedstock, like composition of the binder or amount and hardness of the ceramic particles.
Single phase α-, β- and two phases α/β-sialon composites were sintered with both Nd
2O
3 and Yb
2O
3 by hot isostatic pressing (HIP). The mechanical and tribological properties of these composite ...ceramics have been investigated with respect to their application in direct fuel injection pumps for gasoline engines. Scanning electron microscopy (SEM) was used to analyse the fracture surfaces of sialons following sintering and their worn surfaces after the tribological tests. Microstructural evolution and its change with composition as well as the influence of the microstructural changes on the mechanical and tribological properties have been reported. It has been found that increasing α-sialon phase fraction of the Nd-sialons increases the hardness due to the harder nature of this phase, whereas no significant change in the indentation fracture toughness was observed. Increasing Nd content in these sialons resulted in no significant change in both of the hardness and fracture toughness values. On the other hand, single phase Yb-α-sialons showed a slight decrease in the hardness and a gradual increase in the fracture toughness with increasing Yb content. In a comparative way, it can be seen that Yb-doping gives slightly higher hardness and toughness than Nd-doping. This has been explained by the difference between the cationic radii of Nd
3+ and Yb
3+ and the corresponding ionic field strength. Increased ionic field strength of the Yb
3+ in Yb-sialons resulted in an improvement in their mechanical properties. Tribological tests were performed using a laboratory tribometer with ball-on-plate geometry in reciprocating sliding contact under lubrication with isooctane. Based on the friction and wear data, a relative ranking of the different wear pairs of Nd- and Yb-sialon plates together with a commercial Si
3N
4 plate (used as a reference material) against Si
3N
4 ball was established. Sliding pairs of Yb-doped α-sialon ceramics showed higher friction coefficient and lower wear resistance compared to Nd-doped β- and α/β-sialon composites and the commercial Si
3N
4 ceramic. The lowest friction and the highest wear resistance were measured for the Nd-doped sialon with an α:β-ratio of 88:12. SEM micrographs of the worn surfaces revealed that the main wear mechanisms were microabrasion and tribochemical reactions that resulted in the formation of a thin tribolayer composed of compact wear debris in the tribocontact.
