This paper presents a study on the influence of anisotropically shaped texture arrays on friction behaviour of an oil lubricated sliding contact, especially on directional friction control based on ...the diverging and converging characteristics of the textures. Experiments have been conducted on a TE77 reciprocating cylinder-on-plate test rig, where steel rollers were used to slide against steel plate samples with or without textures. A mineral base oil was used to lubricate the contacts. Three geometries of dimples were designed and laser textured on the steel plate samples with varied 3-dimensional features, including Square Flat (SF), Square slope (SS) and Triangular Flat (TF) shapes representing the shape in x-y (top view) and x-z (side view) planes respectively. These shapes were chosen to vary the converging and diverging properties of the lubricated contacts depending on the sliding direction. Relatively large dimple sizes (side length ~500μm and depth ~10μm) have been used in this study to enable observation of the effect and easy control of the texturing process. The texture density has been kept at 10% as most literature suggested. The large dimple sizes resulted that the dimples were not be fully covered by the contact area, i.e. the dimple sides were bigger than the Hertzian contact width of the roller-flat contacts. This has eliminated the ‘lift’ or ‘load bearing’ effect discussed in most papers thus focuses on other effects investigated in this study. The results show that beneficial effects of the anisotropic textures present in all lubrication regimes including the boundary, mixed and hydrodynamic lubrications, especially under prevailing boundary lubrication conditions. Using high sampling rate for the friction data during the tests, it was able to study local friction effect due to individual dimple array especially at their leading and trailing edges. The results show that a local friction reduction is observed at the leading while an increase at the trailing edge. Overall directional friction effect of the anisotropic textures has been observed that the converging shape in both y-z plane and the x-y plane reduces friction. Furthermore, it was found that the triangular shape dimples have a greater local frictional response at each dimple array, while the sloped bottom square dimples have a more significant overall directional fricition effect.
•Femtosecond laser surface texturing is employed to avoid rims around dimples.•Directional friction effects are observed with anisotropically textured surfaces.•Friction reduction effect is observed with dimples’ size larger than contact width.•Maximum friction reduction effect is observed in boundary lubrication regime.•The real contact length between the contact surfaces is crucial for local friction.
This study provides a new insight on the EHL regime in time-varying conditions. A full-analytical resolution of the Reynolds equation was proposed considering forced oscillations. Confronted to ...experimental validation, the analytical film thickness equations provide perfect modeling of the film forming mechanisms: squeeze induced by the transient evolution of the film thickness with time, asymmetry and hysteresis in the film distribution resulting from the change in direction and the transport effect. Furthermore, the analytical equations combined with a modulation of the inlet flow give an accurate prediction of the effects induced by the starvation resulting from the change in direction, i.e. as the original outlet zone becomes the next inlet zone.
•An analytical of the Reynold’s equation by considering the time dependence.•The measured and calculated lubricant film thickness time evolution is hysteretic.•The squeeze and the residence time influence is retrieved in the calculation.•A starvation effect is produced by the cavitation wake crossover during sliding.•The starvation is calculated with an adaptation of Chevalier’s reduction parameter.
Nanocrystalline Al-Ni-Gd-Co alloys with exceptionally high hardness have been recently developed from amorphous precursors. In the present work, the reciprocating sliding wear in the gross slip ...regime of these novel nanocrystalline Al-based alloys has been investigated under small amplitude oscillatory sliding motion using a martensitic chrome steel as the counter material. When compared to pure Al or Al-12Si alloy, these nanocrystalline alloys exhibit excellent wear resistance and a lower coefficient of friction when sliding against steel. The enhanced wear resistance of the novel nanocrystaline Al alloys is related to their ultra-high hardness and the hybrid nanostructure that mainly consists of nanometric intermetallic phases embedded in a nanocrystalline fcc-Al matrix. Three body abrasive conditions were created at the initial stages of the wear tests due to the formation of micro- and nano-particulate debris from the worn surface of the Al alloys; the debris was compacted under the subsequent sliding cycles forming layers that are protective to the extensive wear of the Al alloys.
•The reciprocating sliding wear behavior of high-strength nanocrystalline Al-based alloys has been studied.•The nanocrystalline Al alloys exhibit excellent wear resistance than those for pure Al and Al-12Si alloys.•The enhanced wear resistance is related to their ultra-high hardness and the hybrid nanostructure.•The lower friction coefficient is mainly attributed to the formation of surface oxide layers and a tribo-layer of debris.
The influence of surface topography on lubricant film thickness has been investigated for the reciprocating sliding of patterned plane steel surfaces against cylindrical counterbodies under ...conditions of hydrodynamic lubrication. Patterns of circular depressions, grooves and chevrons were used, and the fractional area coverage, depth, width and sliding orientation relative to the texture were systematically varied. Textured samples with features much larger than the elastic contact width gave film thicknesses, which were smaller than those for non-textured samples. This effect was more significant for larger features. For patterns composed of circular pockets, maximum film thickness was achieved for an area coverage fraction
f≈0.11. Chevron patterns pointing along the sliding direction gave higher film thicknesses than those pointing across. For an area coverage ratio of ca. 0.06, maximum film thickness was achieved for a feature depth to width ratio of about 0.07. Among the patterns investigated, chevrons were the most effective and grooves the least effective in increasing hydrodynamic film thickness.
During hinges manufacturing, a particular die wear was discovered in the step of cold plastic rolling (CPR)
.
This experimental work deals with the investigation of the tribological behaviour of ...tool-workpiece material pairs: a cold work tool material (X160CrMoV12) sliding against a carbon steel sheet (S235JR) used in the CPR operation. The development of a new and special tribological test designed to simulate conditions corresponding to the CPR process was accomplished. The friction tests were completed using the reciprocating sliding tribometer taking into account the opened tribosystem and the X160CrMoV12 pin sliding orientations. The SEM-EDS characterization of the pin surface revealed an abrasive wear associated with adhesive wear when the pin slides perpendicular to the rolling direction of the plate, but no relevant difference was shown in the friction coefficient values obtained by the pin sliding perpendicular or parallel to the rolling direction of the plate. Then, the influence of deposition of Ni-B 25mL/L TiO
2
sol composite coating on the wear behaviour of the pin and the plate was completed. The applied coating weakens and softens the contact zone between the plate and the pin due to its low roughness (0.12 μm). Indeed, the friction coefficient is reduced to 0.2 and the pin track width decreases from approximately 1520 to 1351 μm upon a sliding distance of 65 m. Also, the coated pin provides an important protection to the S235 JR plate from wear damage as the wear volume of the friction track decreased by over 68% and the wear depth diminished by almost 42% at the end of the sliding distances.
TiAlN has been one of the most extensively investigated hard coatings in laboratory as well as in real life applications. However, a new ternary nitride AlCrN with high percentage of aluminum and ...superior properties has become the subject of ever-increasing interest. Therefore, it is worthwhile to investigate the tribological behaviours of AlCrN versus TiAlN coatings with focus on their wear mechanism.
AlCrN and TiAlN coatings were deposited on cemented carbide by the arc-physical vapor deposition. Microhardness as well as nanoindentation tests have been performed to characterize the mechanical properties of the coatings. Reciprocating sliding and ball-on-disc wear tests against 4
mm diameter Si
3N
4 balls have been performed on the CETR UMT-2 test system. The coating surfaces and wear scars were evaluated by scanning electron microscopy (SEM), energy dispersive X-ray spectrum (EDX), X-ray diffraction (XRD) and laser confocal scanning microscope (LCSM). The results showed that the AlCrN coating exhibited lower friction coefficient and wear rate than those of the TiAlN coating under same testing condition. Combination of abrasive and oxidative wear was the main wear mechanism for the AlCrN and TiAlN coatings in both types of the sliding wear tests, in which the tribo-oxidation played an important role. However, for the ball-on-disc testing, an extra thin transferring film was formed in the center area of the wear track probably due to the different wear debris behaviours as a consequence of the different relative sliding modes. The AlCrN coating presented better performance of anti-oxidation and anti-spalling as compared with the TiAlN coating.
Surface texturing with lubricant mixtures was studied by dynamic coefficient of friction (COF) values on micropit and micropillar WC-Co hard metal specimens that were fabricated using a micro-working ...robot technique combined with metal injection molding (MIM). Lubricating grease mixed with MoS2 was investigated, and 40 wt% additive level of MoS2 reduced COF values by 45% down to 0.06 level on flat WC-Co specimens. The corresponding COF values for the micropit specimens were higher up to 0.10 that may result from the small contact area of the used pin. On the contrary, a reduction of COF values was observed for micropillar specimens compared to the flat WC-Co specimens induced by a load carrying structure of the micropillar specimen. A highly stable antiwear behavior was observed for specimens with micropits.
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•Microstructured hard metal WC-Co specimens were fabricated using metal injection molding (MIM).•Coefficient of friction (COF) values were measured for micropillar and micropit specimens under lubrication.•Addition of 40 wt% MoS2 into the lubricant resulted in a 45% decrease of the COF value for the flat specimen.•Micropillar samples displayed a lower COF values than the micropit specimens.•Micropit specimens displayed a high antiwear behavior.
The aim of the present work is to understand the reciprocating sliding friction and wear behaviour of manganese phosphate coatings that are deposited onto mild steel substrates by a wet-chemical ...process. All tribological tests were performed under dry conditions with a translatory oscillation tribometer for up to 500 oscillating cycles with contact pressures from 750 to 2000 MPa on three materials: (a) uncoated substrate (1.0037 mild steel), (b) manganese phosphate (Mn-P) and (c) manganese phosphate coated with prior activation (A & Mn-P) using steel ball as a counterpart. A significant difference in the frictional performance among the two different phosphate coatings was not seen. Nevertheless, the two different phosphate coatings showed diverse wear mechanisms compared to mild steel.
•Stable behaviour in friction for coated specimens with increase in contact pressure.•In Mn-P, oxide wear, crushing of grains and plastic deformation are dominant wear mechanisms.•In A & Mn-P, crushing of grains and cracking are dominant wear mechanisms.•A & Mn-P showed better wear protection compared to Mn-P.
Low-cost beta (LCB) alloy (Ti-6.8Mo-4.5Fe-1.5Al) is developed specifically for non-aerospace (e.g. automotive and motor sports) applications. However, as for all other titanium alloys, LCB alloy is ...characterised by a high and unstable coefficient of friction and a strong scuffing tendency. Hence, a new surface engineering process based on optimal integration of bulk heat treatment with surface ceramic conversion has been developed, and this paper reports the tribological performance of surface engineered LBC titanium alloy. TEM analysis carried out on the microstructure of the ceramic conversion layer. Reciprocating pin-on-disc sliding wear tests were conducted against both WC and hardened steel balls under unlubricated and oil lubricated conditions. Post-examination of the wear tracks, counterparts and wear debris was carried out to investigate the wear mechanisms involved.
The experimental results show that the wear resistance of the LCB alloy can be improved by 4–16 times by the novel combined bulk/surface treatment; the coefficient of friction is reduced from 0.8 to 1.0 for the untreated material to 0.2–0.4 for the treated samples. The wear mechanisms evolve from severe adhesive wear for the untreated material to mild abrasive wear for the treated material when sliding against a WC-Co ball in air. However, severe wear to the steel counterpart occurred and hence large frictional forces formed, which led to delamination wear of treated surfaces. It is also interesting to find that oil lubrication cannot reduce but rather increases the wear of treated surfaces especially when sliding against a hardened steel ball mainly due to oil pressure induced delamination wear.
•Novel hybrid bulk/surface treatment of LCB Ti alloy.•Significantly increased wear resistance by 4–16 times.•Reduced coefficient of friction from 0.8–1.0 to 0.2–04.•Explanation of some seemingly abnormal wear phenomena.
The sliding wear and friction behaviour of new developed WC‐stainless steel composites without and with carbon addition were evaluated using a linearly reciprocating sliding tribometer under ...ball‐on‐flat configuration, sliding against an alumina ball under unlubricated conditions. The wear of both, discs and ball were measured for different applied loads, sliding distances and frequencies. Worn surfaces were investigated by using microscopy and topography techniques. Comparative experiments were performed using flat samples of a conventional WC–Co composite. It was found that the WC–Co grade displayed an undoubtedly better sliding wear resistance and lower coefficient of friction if compared with the newly produced WC‐SS composites.
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