Dry fretting wear tests were performed on a semicrystalline polytetrafluoroethylene PTFE cylinder rubbing on a flat Ti-6Al-4V surface at room temperature. Various sliding speeds and normal loads were ...imposed for test durations from 5×104 to 106 cycles. The purpose of the investigation was to evaluate how sliding speed and normal load influence friction and wear rate evolution for gross slip fretting-reciprocating sliding conditions. Analysis confirmed an initial transient regime related to the progressive formation of a PTFE transfer film on the titanium counterface, followed by a linear steady-state wear regime. Focusing on the steady-state wear regime, a rising staircase evolution versus sliding speed was observed for both friction and Archard's wear rate. This continuous “sigmoid” wear rate evolution was related to friction heating, inducing transition from micro to macro surface-ploughing wear damage. In addition, a discontinuous cracking wear component was observed from a threshold sliding speed (vth=12mm/s), due to friction-induced thermal activation of the crystalline phase transition then the principal transition (associated with the glass transition) of the PTFE polymer. The analysis also showed that an increase in normal load induced a parallel reduction in the coefficient of friction and parallel increase in wear rate. These parallel evolutions suggest no direct interaction between sliding speed and normal force. Hence the normal force effect can be analyzed using a (P/Pref)n weight function, where the n exponent quantifies the relative effect of normal load versus friction and PTFE wear rate. These results, which are discussed regarding former research works of Tanaka, are correlated with PTFE thermo-mechanical response, friction thermal considerations and competition between several wear processes. Finally, global wear rate could be formulated, including sigmoid (ploughing wear), bell shape (cracking wear) and weighted (normal force effect) functions. Good correlation between experiments and predictions confirmed the stability of this formulation.
•Friction and wear rate analysis of a PTFE / Ti-6Al-4V fretting interface.•PTFE wear rate is expressed by “sigmoid-bell” function of sliding speed.•PTFE wear rate is expressed by weighted function of normal load.•PTFE wear and friction responses depend on interfacial temperature.
Electronic connectors are extensively used in the car industry. However, due to engine vibration, fretting wear damage can decay the electrical contact resistance. In addition to small fretting ...oscillations, the connectors are subjected to clipping/unclipping, which also affects the Electrical Contact Resistance (ECR) endurance (i.e., Nc fretting cycles when ΔR>ΔRc=4mΩ). To investigate this complex tribological process, an homogeneous Ag-Ni / Ag-Ni (2µm) contact was subjected to constant fretting sliding (δ*g=±9µm) combined with intermittent millimetric reciprocating sliding. The analysis showed that, by transferring silver material from the reciprocating track to the fretting scar, ECR endurance was linearly increased. The larger the reciprocating stroke (D from 0.25mm to 1.5mm), the greater the endurance. Besides, if the Nf fretting period between reciprocating sliding sequences was too long, the positive effect of the reciprocating was reduced. Expressing both reciprocating silver transfer kinetics and fretting wear rates, a global model of ECR endurance is proposed.
•Electrical contact resistance endurance (ECR) of Ag/Ag plated fretting contact.•Investigation of combined fretting and reciprocating sliding conditions.•Reciprocating by transferring silver in fretting scar increases the ECR response.•Explicit formulations of ECR as a function of the reciprocating stroke.•Explicit formulations based on an Ag fretting wear rate approach.
Purpose This paper aims to study the different infill, printing direction against sliding direction and various load condition for the friction and wear characteristics of polylactic acid (PLA) under ...reciprocating sliding condition.
Design/methodology/approach The tests were performed by applying the load of 1, 5, 15 and 10 N with sliding oscillation frequency of 10 Hz for the duration of 10 min at room temperature.
Findings The results show that the friction and wear properties of PLA specimen change with a different infill density of printed parts. The oscillation frequency is 10 Hz and the infill density of plate is 50 per cent that shows the best friction and wear properties.
Originality/value The potential of this research work is to investigate the tribological characteristics of three-dimensional printing parts with different infill percentage to provide a reference for any parts in contact with each other to improve friction and wear performance. There will be many opportunities exist for further research and the advancement of three-dimensional printing in the field of tribology.
While titanium and its alloys have an excellent balance of properties, they continue to have limited applications owing to their relatively poor wear resistance, in particular for commercially pure ...titanium. Processing by severe plastic deformation (SPD) has been developed over the last two decades that produces an ultrafine-grained (UFG) microstructure resulting in improved mechanical properties. However, only limited studies are available to date on the wear behavior of SPD-processed UFG metallic materials with many conflicting results in terms of reduced wear rates. Furthermore, the wear behavior and mechanisms of SPD-UFG metallic materials are unknown in self-mated sliding contacts. Here, the friction and wear properties of self-mating UFG titanium in a cross-cylinder high frequency reciprocating contact is reported and compared to coarse grain (CG) titanium. Cross-sectional focused ion beam microscopy, transmission electron microscopy, and Raman spectroscopy studies were performed inside worn surfaces to determine the dry sliding wear-induced structural and chemical evolution responsible for the observed friction coefficients and wear rates. It was determined that the microhardness of UFG titanium increased from 2.6 to 3.4GPa; however, this increased hardness did not correlate to lowering of friction and wear. Instead, the similar friction coefficients and wear rates of CG titanium and UFG titanium were due to similar wear surface structures and oxide debris composition. Furthermore, wear surface morphologies and cross sections inside the wear tracks revealed that CG titanium had a major shear deformation contribution to wear, but with the wear rates being equivalent, wear is most likely dominated by oxide particle abrasion.
An in situ observation system was developed to monitor the magnetic domain structure in the process of rubbing. By means of this system, the magnetic domain motion beneath the sliding area was ...observed while a carbon steel 1045/316 L stainless steel pin specimen rubbed on a pure iron block specimen under certain loads. Experiments showed that plastic deformation stimulated changes in magnetic domain beneath the rubbing surface as a result of sliding friction, which means plastic deformation was a crucial activation factor for tribo-magnetization. Then the variations of the magnetic domain structure beneath the rubbing surface with the increasing of rubbing cycles were characterized. From experimental results the relation between plastic deformation in tribological process and the original process in mechanism of the tribo-magnetization phenomenon was discussed.
•An in situ observation system was developed to perform the tests.•The stretching directions of domain walls turned into the same direction.•Final directions of domain walls were perpendicular to sliding surface.•The walls of the original domains changed from straight lines to irregular curves.•Plastic deformation was a fatal activation factor for tribo-magnetization.
The tribological behaviors of Ti-Ni51.5 at% alloy strengthened by finely dispersed Ni
4
Ti
3
particles in reciprocating sliding against GCr15, Al
2
O
3
, and ZrO
2
at room temperature were studied. ...Interestingly, the coefficient of friction (COF) suffered a sheer drop (from 0.9 to 0.2) when the aged alloy slid against GCr15 at a frequency of 20 Hz under a 20 N load without lubrication. However, severe-mild wear transition disappeared when a solutionized alloy was used. Moreover, the COF stabilized at a relatively high level when Al
2
O
3
and ZrO
2
were used as counterparts, although their wear mechanisms showed signs of oxidation. Scanning electron microscopy (SEM) and X-ray element mappings of the wear scars of the counterparts clearly indicate that the formation of well-distributed tribo-layer and material transfer between the ball and disk are pivotal to the severe-to-mild wear transition in the aged Ti-Ni51.5 at% alloy/GCr15 friction pair. The higher microhardness and superelasticity of the aged alloy significantly accelerate the material transfer from GCr15 to the disk, forming a glazed protective tribo-layer containing Fe-rich oxides.
Surface texturing has been shown to be an effective modification approach for improving tribological performance. This study examined the friction reduction effect generated by square dimples of ...different sizes and geometries. Dimples were fabricated on the surface of ASP2023 steel plates using femtosecond laser-assisted surface texturing techniques, and reciprocating sliding line contact tests were carried out on a Plint TE77 tribometer using a smooth 52100 bearing steel roller and textured ASP2023 steel plates. The tribological characterization of the friction properties indicated that the textured samples had significantly lowered the friction coefficient in both boundary (15% improvement) and mixed lubrication regimes (13% improvement). Moreover, the high data sampling rate results indicated that the dimples work as lubricant reservoirs in the boundary lubrication regime.
It has been found in recent studies that the main reason for the failure of a biomedical material used as an implant is due to the low resistance of the combined wear and corrosion. The aim of the ...present research study is to investigate the triboelectrochemical behaviour of different biomedical materials used as implants under different contact conditions. Comparative experiments were performed using commercial pure titanium (cP‐Ti), Ti6Al4V alloy, pure niobium (Nb), and a Co28Cr6Mo alloy sliding against a Zirconia counterbody tested in artificial saliva. The corrosion potential of the working electrode was monitorised using the open circuit potential technique, and potentiodynamic polarization curves were obtained. It was found that the Nb specimen showed a poor tribological performance, while the Co28Cr6Mo alloy showed the lowest friction and wear. The cP‐Ti specimen showed a more noble behaviour than that of the other three specimens with the highest corrosion potential value.
Triode plasma nitriding was used in conjunction with electron-beam plasma-assisted physical vapour deposition of TiN and CrAlN to enhance the wear resistance of Ti–6Al–4V titanium alloy. Linear ...reciprocating-sliding ball-on-plate wear tests were performed to assess the tribological performance of the treated alloy. Wear volumes were correlated to changes in coefficient of friction, which is often indicative of breakdown of the surface treatment. Debris generated during wear testing was characterised using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD) and laser diffraction for particle size analysis. Surface micro-profilometry and SEM were used to characterise the wear scars. The results obtained indicate that, in order to assess the relative improvement in wear behaviour attained by using surface treatments it is insufficient to compare linear wear rates alone. A clear comparison is only possible if testing is carried out in steps of increasing sliding distance, until the treated/deposited layers have been completely removed. Also, it is shown that the number of repeated tests necessary to evaluate clearly the treatment and/or coating can vary substantially, depending on the observed test progression; typically this necessitates the greatest number of repeats around the point of wear at which the ball counterface contact area is in transition from the treatment layer(s) to the substrate bulk. The inherent variability in wear performance under linear ball-on-plate reciprocating-sliding is correlated to debris generation, changes in relative humidity – and the resultant wear mechanisms involved.
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