Surface Tribological Performance Research Articles

ASSESSMENTS ON THE FRICTION AND WEAR BEHAVIOR OF SOME POLYMERIC MATERIALS USED IN SLIDING CONTACTS

The effects of friction on polymeric materials are quite difficult to explain due to the micro and macroscopic interactions of the friction coupling surfaces, which slide over each other. The friction and wear behavior of surfaces in sliding motion can be considered important design criteria. By adding different concentrations of reinforcing agent to the base material, the tribological performance of surfaces in sliding motion can be obtained. The experimental study was carried out on a pin-on-disc type tribological stand under dry friction conditions. The friction and wear behavior was analyzed for two base materials (PTFE and PA66) and the same glass fiber reinforced materials (PTFE + 25% fiber-glass and PA66+GF30). The tests were carried out at different sliding speeds and loading forces, v1=0.20 m/s, v2=0.50 m/s, v3=0.75 m/s and loading forces, Fn1=1.0 N, Fn2=2.5 N, Fn3=5.0 N over a friction length of 5000 mm. Research has shown that the coefficient of friction decreases with increasing loading force. Tests have shown that a high value of the friction coefficient does not mean a high wear rate, the wear rate values are between 10-12 and 10-15 m2/N. TheL(1) presences of the reinforcing agent in the base material have a significant importance on the friction and wear behavior under the action of operating factors (load, sliding speed).

Tribological behavior of zirconia ceramic with micro-channels produced by nanosecond laser

Tribological performance of surface can be improved by laser texturing. For this purpose, this paper fabricated the grid-texture composed of micro-channels by nanosecond laser on the zirconia surface. To obtain micro-channel with high-quality, the effect of laser parameter on the morphology and geometry of micro-channels was investigated. The results showed that the laser power has lest effect on the taper angle and the height of pile up. Analysis of chemical properties indicated that a deoxidation reaction by laser irradiating can led to oxygen vacancy decreasing and color darkening, and this color variation can be diminished by the annealing treatment. Analysis of phase properties showed that internal stress resulting from oxygen vacancy decreasing can led to the tetragonal → monoclinic phase transformation. Finally, grid-textures composed by micro-channels with better quality obtained from the experimental results were fabricated to change the tribology of zirconia. Results of wear tests indicated that the coefficient of friction for the laser-treated is higher and more stable than that of untreated. The observation of worn surface indicated that adhered lamellar for laser-treated was less than that on the untreated surface, and abrasive particles can be observed in microgrooves produced by laser, which can decrease ploughing effect to improve the friction stability.

Influence of residual stress on the sliding wear of AISI 4340 steel

Mechanical components and structures wear out as a result of friction between surfaces in relative motion. Residual stresses play an important role for the tribological performance of components since compressive residual stresses yield positive effects on wear resistance. However, the real effect of residual stresses on the tribological performance of surfaces is not entirely clear. The objective of this work is to evaluate the residual stress behavior during a pin-on-disk wear test of quenched and tempered AISI 4340 disk specimens against a counter-body of steel AISI E 52100. Tests were performed in shot peened and non-shot peened specimens in six steps and residual stresses were evaluated after each one by X-ray diffraction technique using sin2 method. The results shown that wear rate of the shot peened specimens was approximately fifty percent lower. Shot peening induced compressive residual stresses contributed to this effect even though they were modified during the pin-on-disk test. Keyword: Residual stress, X-ray diffraction, AISI 4340 steel, Wear, Pin-on-disk test, shot peening.

Tribological performance of surface with different wettability under ball-on-disc test

This paper proposes an innovative and reliable method to reduce friction and wear using a robust lyophobic surface with microstructures. The tribological performance of four kinds of surfaces, including a microstructured surface (MS) without low surface energy treatment, a lyophobic microstructured surface (LMS), a robust lyophobic microstructured surface (RLMS), and an untextured surface (US), were investigated using ball-on-disc testing with lubrication. The experimental results indicate that compared to the US sample, the RLMS sample fabricated with the proposed method reduced the friction coefficient by approximately 21.6%. In addition, the wear mass loss of the RLMS was reduced by 36.42% under specific conditions compared to the US sample. Furthermore, the antifriction mechanism of the robust lyophobic microstructured surface is analyzed and discussed in detail.

Multi-scale surface patterning to tune friction under mixed lubricated conditions

It is well accepted that the tribological performance of surfaces can be directly correlated with their energy efficiency and lifetime. Consequently, surface patterning has gained great attention to manipulate friction and wear under dry and lubricated conditions in the last 2 decades. Inspired by multi-scale surfaces found in nature, direct laser interference patterning (finer cross-pattern) and hot micro-coining (coarser hemispherical patterns) were used to create multi-scale patterns on stainless steel substrates. Using a ball-on-disk set-up, the running-in behavior and the maximum oil film lifetime were characterized for all single- and multi-scale patterns under mixed lubrication. Compared to the polished reference, all patterned surfaces helped to prolong the oil film lifetime. Synergetic effects induced by multi-scale patterns were observed leading to the best performance of the sample combining deep micro-coined patterns (intermediate area density) with the additional laser pattern. As a result of the additional hydrodynamic pressure generated by the finer laser pattern and the oil reservoir effect as well as the entrapment of wear particles induced by the coarser micro-coined pattern, the oil film lifetime was extended by a factor of 200 (200 times).

Shakedown limits on coated and engineered surfaces

When a hard rough surface slides repeatedly on a softer component a system of protective residual stresses may be developed in the near-surface layers of the weaker material which enable loads sufficiently large to cause plastic deformation in the early cycles of loading to be accommodated purely elastically in the later stages of the loading history. This is the process known as shakedown and limits on the intensity of loading consistent with the eventual cessation of plastic deformation for uniform half-spaces are now well established. However, components liable to face arduous tribological conditions are traditionally heat-treated to produce a hardened thin outer layer over a softer core; this gradation of hardness or plastic strength within a material of constant elastic properties leads to changes in the shakedown analysis and thus in the way the results are most conveniently presented in maps or charts. More recently introduced techniques of surface engineering often rely on the deposition of a well-bonded hard coat on a softer substrate so that both the elastic and the plastic properties of the coating differ from those of the underlying material; these differences present further difficulties in formulating and displaying the corresponding shakedown limits. In addition to the values of hardness and stiffness of the coating and those of the substrate, important system parameters are the thickness of the elements of the coating (in comparison to the characteristic dimension of surface roughness) the integrity of the interlayer bonds and the coefficient of friction between the coated component and the surface against which it slides. The results of a sequence of studies into these effects are displayed in the form of non-dimensional shakedown charts or maps which demonstrate to the materials engineer or designer the potential improvement that might accrue from optimal surface engineering. These also indicate the conditions under which, because of an excessive mismatch between the mechanical properties of the coating and the substrate, inappropriate surface treatments may lead to either no significant improvement or, in some circumstances, even a degradation in surface tribological performance.