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The ice friction behavior of various microtextured polymer surfaces was studied with respect to ice temperature and applied load using a customized linear tribometer. Similar micropillar patterns were replicated on polypropylene and two rubber compounds, and when hierarchical micro–micro textures were present, all the materials exhibited superhydrophobicity. Taller protective micropillars were shown to be crucial for protecting the smaller microtextures from abrasive wear. The mechanical properties of the polymers affected the sliding friction of the microtextured surfaces on ice. High loading of hierarchical textures on rigid polypropylene or operation near the ice melting point tended to increase its adhesion tendency or resisting behavior. The sliding performance of the hard and soft rubber compounds was temperature-dependent, and the texture on the soft rubber influenced the sliding friction differently depending on the ice temperature. Consequently, textural modifications of the sliding surface enabled a certain degree of control over the sliding friction behavior on ice. Unlabelled Image • Rubber and PP surfaces were hierarchically micro-micro textured for friction studies. • Material hardness affects ice sliding friction of microtextured surfaces. • Sliding friction of textured soft rubber depends on the ice temperature. • Hierarchical texture on hard polymers can induce sticky sliding on ice. [ABSTRACT FROM AUTHOR]

Abstract Elastomers are currently used intensively in various industrial applications. However, their deployment in dry tribological contact is normally inhibited by their poor dry sliding friction behaviour due to their intrinsically high adhesive characteristics. This problem is normally addressed in the industry by using various fluid (greases or oils) or solid (coatings or lacks) lubricants. Alternatives to the use of lubricants for tribosystems involving elastomers exist in the form of modifications of the elastomer composition or by reducing their effective nominal contact area by using surface texturing. The latter approach of reducing the adhesive nature of elastomers by surface structuring is the main focus of the present study. Two different micro-sized structures (consisting of micro-pits) were produced on thin Al inlays using a microscopically scaled punching process. These inlays were thereafter glued onto laboratory-scale injection moulds. These micro-pitted moulds were subsequently used to produce injection moulded micro-pillared L iquid S ilicone R ubber (LSR) pads. The present study was focused on three different aspects: 1. Determination of the degree of replication of microstructures from injection moulds to the surface of LSR pads; 2. Evaluation of any possible friction reduction induced by a decrease of the nominal contact area through micro-texturing of LSR pads in dry tribological tests; and 3. Evaluation of the wear resistance of micro-pillared LSR pads under dry conditions. The results have shown that successful production and relatively accurate replication of micro-pitted structures from injection moulds onto LSR pad surfaces in the form of micro-pillars may be achieved. Furthermore, it was shown that a decrease of the effective nominal contact area through micro-pillars may enable a reduction of friction in comparison to the benchmark (unstructured LSR pads), but only for low normal loads where the adhesive component of friction is playing a determining role. Finally, wear tests have shown that the wear resistance of both micro-pillared structures produced on LSR pads under dry conditions against Al or PA6.6-GF30 was relatively poor. Both structures exhibited extensively worn regions after a testing distance of 11 m: structure 1 showed a larger worn area ratio than structure 2 (ratio worn area/total area ~45%–60% for structure 1 and ~30% for structure 2). Highlights • Production of micro-pits in thin Al inlays using a microscopically scaled punching process is highly feasible. • High accuracy reproduction of micro-pits from Al inlays as moulded micro-pillared LSR pads has been successfully achieved. • At normal loads >150 N(adhesive friction as secondary role), micro-pillared pads have friction coefficients similar to benchmark. • At normal loads <40 N(adhesive friction is predominant), reduction of friction coefficients by a factor of 2 may be realized. • Both micro-pillared structures possess relatively poor wear resistance when tribologically tested in dry conditions. [ABSTRACT FROM AUTHOR]

Tribological conditions in bulk metal forming processes are characterized by high contact pressures and large relative movements at high velocities between the tool and the workpiece. In addition, significant surface enlargements and elevated temperatures can occur. It is very challenging to reproduce such contact conditions on pin-on-disc tribometers. In this study, a method for simulating the contact conditions of a metal forming process on a pin-on disc tribometer is presented. Special test samples have been designed in order to achieve high contact pressures and surface enlargements with a homogeneous distribution of these quantities within the contact zone. It is shown that the test method delivers reproducible results and enables the detection of small changes of the contact conditions. Furthermore, microstructural changes of the real contact surface can also be simulated, which was verified by SEM imaging. [ABSTRACT FROM AUTHOR]

The influence of temperature on friction and wear of unlubricated DIN 100Cr6 steel/steel contacts was studied in different anaerobic gaseous atmospheres, namely argon (Ar), nitrogen (N 2 ) and carbon dioxide (CO 2 ), and air atmosphere was used as benchmark. Tribological experiments were performed at high temperature (200 °C) and the results were compared with previously published results from experiments performed at ambient temperature (20 °C). Reciprocating ball-on-disc tribological tests were conducted with high contact pressures (maximum initial contact pressure of 1.5 GPa). In all anaerobic gas atmospheres at high temperature, lower friction and wear were measured than in air atmosphere. The lowest friction and wear were measured in CO 2 atmosphere; they were slightly higher in N 2 atmosphere and even more slightly higher in Ar atmosphere. In all anaerobic atmospheres, different oxidation kinetics of steel surfaces occurred as compared with air atmosphere. For N 2 and CO 2 atmospheres, XPS analyses of the wear debris showed an increased concentration of non-carbidic carbon and furthermore for the CO 2 atmosphere, iron–carbon–oxygen layers were also found which probably provided the very favourable friction and wear properties observed in this atmosphere. In N 2 and CO 2 atmospheres, higher wear and friction were observed at high temperature than at ambient temperature, which indicates that at high temperature, a deterioration of the beneficial properties of the N 2 and CO 2 -reacted tribolayers occurred. On the contrary, in Ar atmosphere at high temperature, a decreased adhesion and a significantly lower wear as compared with ambient temperature was observed. [ABSTRACT FROM AUTHOR]

It is generally known that gaseous atmospheres can significantly affect the friction and wear behaviour of non-lubricated contacts; however there still exists a lack of knowledge on the subject, since the tribological behaviour and the tribochemistry of the gas-lubricated systems are highly sensitive to the selection of the operating parameters, and the results from available literature are often scattered and sometimes even contradictable. This study was focused on the identification of the friction and wear mechanisms of technical gases used at atmospheric gas-pressure in non-lubricated DIN 100Cr6 (AISI 52100) bearing steel contacts at severe operating conditions (high-frequency oscillation at high contact pressure). Argon (Ar), nitrogen (N 2 ) and carbon dioxide (CO 2 ) were used as gas atmospheres and air atmosphere was used as a reference. The gases are analysed in terms of their chemical reactivity with the steel surfaces and a correlation between the properties of different tribochemical products and the observed friction and wear mechanisms is made. In N 2 and CO 2 atmospheres, wear was significantly lower than in air atmosphere, with a wear reduction comparable to the effect of using a liquid lubricant. In N 2 atmosphere, a slightly higher friction was measured than in air atmosphere, while in CO 2 atmosphere, friction was 60% lower than in air atmosphere. In Ar atmosphere, both friction and wear were slightly higher than in air atmosphere. With X-ray photoelectron spectroscopy (XPS) of the wear particles, it was observed that the concentrations of different tribochemical products and their mutual ratios critically determine the friction and wear behaviour of the non-lubricated steel contact. [ABSTRACT FROM AUTHOR]

Total electron yields from highly oriented pyrolytic graphite (HOPG) have been measured for perpendicular impact of H+, C+, N+, and O+ projectile ions with kinetic energies from a few hundred eV up to 30 keV. The data are interpreted within a model for kinetic electron emission based on non-adiabatic time-dependent perturbation of valence-band electrons by the moving particle. The microscopical parameters of this excitation processes describe well the qualitative trends in the experimental data when changing the target from HOPG to polycrystalline gold. [Copyright &y& Elsevier]