Dry Sliding Contact Conditions Research Articles

Wear Performance of Cu–Cd, Cu–Be and Cu–Cr–Zr Spot Welding Electrode Materials

Heating of the electrode at the work–piece interface zone in spot welding, leading to degradation of the tip, becomes a significant concern in the high-volume production automotive industry. By recognizing the interrelationship between hardness, wear resistance, and thermal conductivity, the authors emphasize the importance of selecting electrode materials with suitable alloying elements desirable for achieving optimal performance in spot welding applications. This paper studies the wear behaviour of three types of spot-welding electrode materials under dry sliding contact conditions. A pin-on-disc tester was used to investigate Cu–Cd, Cu–Be and Cu–Cr–Zr alloys’ wear behaviour under variable parametric load, temperature and time conditions. Taguchi L9 orthogonal array was used to investigate the significance of parameters and their effect on linear wear. The ranking of the parameters was performed using SN ratio analysis. The wear mechanism was also studied using SEM analysis. Abrasive wear was observed at lower loads, while adhesion, oxidation and plastic deformation were observed under high-load and -temperature conditions. This study suggests an alternative to the presently used electrolytic tough pitch (ETP) Cu electrode involving equally good wear-resistance material. However, a detailed investigation on the effect of plasma on the metallurgical characteristics of selected material is suggested.

Tribological performance of PDA/PTFE + Graphite particle coatings on 60NiTi

60NiTi has unique combinations of high shock load and corrosion resistance, which is suitable for load-bearing applications exposed to chemically aggressive environments. However, it exhibits poor tribological properties in dry sliding contact conditions. Polydopamine (PDA)/polytetrafluoroethylene (PTFE) coatings are shown to reduce friction and wear of 60NiTi significantly. In this study, using Si3N4 balls as the counterface material, the effects of adding graphite particles (GrP) to the PTFE layers of the PDA/PTFE coatings on the sliding properties of 60NiTi were studied. The obtained results were compared to those of the PDA/PTFE coated and uncoated 60NiTi. The results showed that both types of coatings significantly decreased the coefficient of friction (COF) and wear of the 60NiTi substrates and the wear of the counterface balls. The PDA/PTFE + 0.25 wt% GrP coatings have less porosity and approximately 2.4 times durability when compared to the PDA/PTFE coatings. Scratch tests on the coated surfaces also revealed better adhesion strength, higher load-carrying capacity, and enhanced transfer films on the counterface balls for the PDA/PTFE + 0.25 wt% GrP coatings. The less porosity, the enhanced adhesion strength, and the transfer film contributed to the longer wear life of PDA/PTFE + 0.25 wt% GrP coatings on 60NiTi.

Tribological performance at high temperatures of alumina coatings applied by plasma spraying process onto a refractory material

Two different Al2O3 coatings manufactured by plasma spraying process were tested under dry sliding contact conditions at high temperatures in order to determine their tribological behavior. At higher temperature than 800 °C, wear rate and mechanisms for Al2O3 coatings have not yet been reported. The results obtained were compared with those from both: an electro-melted Al2O3 refractory used as reference and a pressed & sintered silico-aluminous refractory used as substrate, which were tested under the same conditions. The reference was chosen due to the high performance against wear that this material shows, and the substrate was chosen due to the high potential that this material with low properties against wear shows when it is coated. Crystallographic phases, micro-hardness, Young's modulus and fracture toughness were measured before and after the wear tests, obtaining as results that both Al2O3 coatings showed better wear performance than the pressed & sintered silico-aluminous refractory used as substrate, and even than the electro-melted Al2O3 refractory used as reference. Additionally, in the plasma sprayed coatings, as well as, in the electro-melted Al2O3 refractory, the wear mechanism was controlled by a transformation produced by the increasing in temperature from ductile deformation to brittle deformation, for finally returning to ductile deformation again. The high performance of plasma sprayed coatings was mainly due to the high values of toughness, as well as due to the increasing of the α-Al2O3 levels and therefore, the hardness during the wear tests because of the high temperature, allowing to these ceramic coatings to be a possible way to protect the conventional pressed & sintered silico-aluminous refractories to replace the expensive non-structural electro-melted ones currently exposed to abrasive wear in glass, cement and other primary industries.

Boro-nitriding coating on pure iron by powder-pack boriding and nitriding processes

To alleviate spallation and crack difficulties exhibited by a borided metallic surface when it is subjected to a normal, heavy and sliding load under dry conditions, a boron nitride coating was produced on pure iron in two stages: boriding the iron surface at 950°C for 6h and then nitriding the pre-borided iron at 550°C for 6h. The powder-pack technique was used in both stages. XRD measurements confirmed that the grown layers were nitrides and duplex borides. The produced diffusion of the layers reached 240µm in depth as measured by SEM images. The measured microhardness across the case favoured the interphase cohesion between the iron nitrides and iron borides layers. Consequently, the multicomponent coating exhibited superior wear resistance to an applied normal load under dry sliding contact conditions in comparison to borided iron.

Influence of normal loads and sliding velocities on friction properties of engineering plastics sliding against rough counterfaces

Friction properties of plastic materials are very important under dry sliding contact conditions for bearing applications. In the present research, friction properties of engineering plastics such as polytetrafluoroethylene (PTFE) and nylon are investigated under dry sliding contact conditions. In the experiments, PTFE and nylon slide against different rough counterfaces such as mild steel and stainless steel 316 (SS 316). Frictional tests are carried out at low loads 5, 7.5 and 10 N, low sliding velocities 0.5, 0.75 and 1 m/s and relative humidity 70%. The obtained results reveal that friction coefficient of PTFE increases with the increase in normal loads and sliding velocities within the observed range. On the other hand, frictional values of nylon decrease with the increase in normal loads and sliding velocities. It is observed that in general, these polymers show higher frictional values when sliding against SS 316 rather than mild steel. During running-in process, friction coefficient of PTFE and nylon steadily increases with the increase in rubbing time and after certain duration of rubbing, it remains at steady level. At identical operating conditions, the frictional values are significantly different depending on normal load, sliding velocity and material pair. It is also observed that in general, the influence of normal load on the friction properties of PTFE and nylon is greater than that of sliding velocity.

Frictional Properties of AZ80 and ZE10 Magnesium Alloys Under Dry and Lubricated Contact Conditions

The frictional properties of two types of magnesium alloys, i.e. AZ80 and ZE10 were investigated. A purpose-developed sheet metal forming simulator was used to conduct the experiments under constant plastic deformation. Both lubricated and dry sliding contact conditions were simulated and the effect of key process parameters such as contact pressure and sliding velocity on the frictional properties of these alloys were investigated. Due to the different sliding velocities, the contact pressure rose during each experiment which enables the measurement of the coefficient of friction for a wide range of contact pressures. The results showed an increase in the friction coefficients of both alloys with increasing contact pressure. Furthermore, a decrease of the friction coefficient was observed for higher sliding velocities.

Experimental Investigation of Nano-Composite Coated Stainless Steel (316L) Surfaces under Unidirectional Sliding

This work proposes the investigation of nanosized Titanium Aluminum Nitride (TiAlN) on the Stainless Steel (316L) substrate. A chromium interlayer has been applied over the modified surface which will act as an interlayer between the substrate and hard composite coating. The composite coating was prepared by Magnetron Sputtered-Physical Vapour Deposition (PVD) on chromium coated lapped and textured surfaces of stainless steel substrate. Scratch test was performed to characterize the adherence of the coatings on the substrate. TiAlN surface coating over the textured surface exhibits higher adherence than the lapped surface coating surface. The tribological performance of the wear resistant coatings on lapped and textured surfaces was experimentally investigated by pin on disc tribometer at dry sliding contact conditions under various normal loads. The testing results were compared and the results showed that TiAlN coating on textured surfaces exhibited lower friction coefficient and wear rate than lapped coating surfaces under same testing conditions. Sliding wear characteristics such as coefficient of friction and specific wear rate were investigated.

Influence of surface texture on tribological performance of AlCrN nanocomposite coated titanium alloy surfaces

The modification of surface layer of machine elements used for engineering applications requires modern tools and techniques for improving its functional aspect and enhanced life. In this study, modification of surface layer was done by combining laser texturing and filling the textured surface by hard wear-resistant coating. This study aimed at investigating the friction and wear behavior of nano aluminum chromium nitride (AlCrN) composite coating over modified titanium alloy (Ti6Al4V) surfaces under dry sliding contact condition. The surface of as-received titanium alloy substrate was lapped and laser surface texturing was performed on the lapped surface. Magnetron-sputtered physical vapor deposition technique was preferred for coating. Scanning electron microscope, energy dispersive X-ray and microhardness tests were performed to characterize the coating. Further, to evaluate the bonding strength of coating against modified surfaces, scratch tests were performed by a scratch tester. Using pin-on-disc tribometer, the coated samples were subjected to tribological investigation for dry sliding contact conditions. The effect of normal load on friction and wear characteristics were examined and discussed. The performance of these coatings on textured and lapped surfaces was compared. Critical parameters such as variation in coefficient of friction and specific wear rate were reported. The influence of textured surface on coating performance was discussed.

Frictional and wear performance of polyester composites based on coir fibres

This article presents an evaluation of frictional and wear performance of new polyester composites based on coir fibres. Coir fibre-reinforced polyester (CFRP) composites were developed in a multi-layer form, mainly in three and four layers. The influence of the coir fibres on the wear and frictional behaviour of polyester was evaluated using a block-on-disc (BOD) machine under dry sliding contact conditions against smooth stainless steel. Worn surfaces of the composites were observed using a scanning electron microscope. The friction coefficient and specific wear rate were presented as a function of sliding distance (0-4.2 km) at different applied loads (10-30 N). The results revealed that all test parameters have a very significant influence on the frictional and wear characteristics of the materials. Moreover, a higher coefficient of friction was exhibited in the four-layer composite. CFRP composites based on three layers exhibited better wear and frictional performance compared with the one with four layers and neat polyester. The wear mechanism was predominated by deformation and micro-ploughing in the resinous regions and debonding of fibres.

Influence of surface topography of arc-deposited TiN and sputter-deposited WC/C coatings on the initial material transfer tendency and friction characteristics under dry sliding contact conditions

The influence of surface topography of PVD coatings on the initial material transfer tendency and friction characteristics in dry sliding contact conditions has been investigated. A modified scratch test was used to evaluate the material transfer tendency between ball bearing steel and two different PVD coatings, TiN and WC/C, under dry sliding contact conditions. Post test characterisation of the contact surfaces was performed using SEM/EDS and AES in order to map the initiation points and mechanisms for material transfer. The results show that the resulting topography of the PVD coated surfaces is strongly dependent on both the substrate material topography and the topography induced by the coating deposition process used. In sliding contact with a softer surface the coating topography results in a significant material pick-up tendency of the PVD coated surfaces. The material pick-up is mainly controlled by the abrasive action of hard coating asperities and as a result a polishing post treatment of the as-deposited PVD coatings significantly reduces the material pick-up tendency. For the WC/C coating, showing intrinsic low friction properties, the post treatment inhibits the material pick-up and results in a low and stable friction coefficient ( μ ~ 0.1). For the TiN coating, that lacks intrinsic low friction properties, the post treatment reduces the material pick-up tendency but has no significant influence on the friction characteristics. This is mainly due to the presence of metallic Ti originating from the macroparticles on the TiN coating which results in a reactive surface that promotes a strong adhesion between the mating surfaces.

THE EFFECT OF ROTOR DISC MATERIAL ON TRIBO BEHAVIOR OF AUTOMOTIVE BRAKE PAD MATERIALS

This work aims to investigate the effect of two different counterdisc materials, i.e. gray cast iron (GCI) and ductile gray cast iron (DGCI) on tribo behavior of non-commercial frictional materials (NF1, NF2, NF4, and NF5) and two other chosen commercial brake pads (CMA and CMB) under dry sliding contact conditions. The four non-commercial frictional materials were fabricated with various percentages of phenolic binder resin (15 and 20 vol.%) and reinforced with steel fibers (15 and 20 vol.%) using hot press molding methods. Tribo tests were carried out using a small-scale tribo-tester of pad-on-disc type. Friction coefficient and wear of non-commercial and commercial brake pads were measured against each counterdisc (GCI and DGCI) and compared. Then, the friction and wear characteristic are discussed by comparing the experimental results obtained for each kind of cast iron. The results showed that maximum friction coefficient (0.4–0.5) of brake pad was attained at 2.22 MPa applied pressure and 2.1 m/s sliding speed when the frictional brake pad materials were tested against DGCI disc rotor. Meanwhile, similar wear rates for all frictional brake pad materials were sustained at higher applied pressure and sliding speed when tested against either type of rotor discs (GCI and DGCI). The results on the other hand, indicated that non-commercial materials NF1 and NF4, gave better wear resistance compared to other frictional pad materials. NF2 exhibited the lowest wear resistance when tested against GCI and DGCI rotor disc at all applied pressure and sliding speeds. The latter result is referred to the low percentage binder resin in the friction material NF2.

A study on the potential of sugarcane fibers/polyester composite for tribological applications

The tribo-potential of sugarcane fibre reinforcement in the thermoset polymers for enhancing the adhesive wear resistance has not been explored so far. Hence, the present work aims to explore the possibility of using this natural fibre to reinforce polyester and thus opens a new way to implement locally available inexpensive fibres and produce a new candidate tribo-material for bearing applications. Sugarcane fibre/polyester (SCRP) and glass fibre/polyester (GRP) composites (with chopped fibres of 1, 5, 10 mm length randomly distributed and unidirectional mat fibres) were prepared using compression mould and hand-lay-up techniques. Friction coefficients and wear rates of SCRP and GRP composites were determined under dry sliding contact conditions in parallel and anti-parallel orientations and subjected to different operating parameters such as load, speed and test duration. Results of friction and wear proved that SCRP composite is a promising composite which can be a competitive to GRP composite. In the case of chopped sugarcane/polyester (C-SCRP) composite, very smooth patches of polymer film (protective layer) due to plastic deformation shielded the surface of C-SCRP composite pin from damage by the metallic asperities and thereby contributed to the higher wear resistance. Furthermore, this layer provided enhancement to the bonding of SCFs fibre with matrix. In contrast C-GRP composite produced broken hard particles of GF at the interface which acted as a third body and restrained the formation of such protective layer. Wear resistance of C-SCRP composite increased significantly with increasing load but decreased drastically for C-GRP composite. In addition, wear rate of C-SCRP composite decreased by (20–50%) when the fibre length increased from 1 to 5 mm. With further increase in the fibre length to 10 mm, the wear rate was no longer decreased instead increased drastically by 40–70%. Besides C-SCRP composite gave friction coefficient of the same order as C-GRP composite. Unidirectional sugarcane/polyester (U-SCRP) composite showed lowest wear resistance when fibre was oriented parallel to sliding direction. But when this composite tested in AP-O, wear resistance was almost the same as the CM-GRP composite. Moreover, the U-SCRP composite exhibited lowest friction coefficient when tested in AP-O and highest when tested in P-O, suggesting that reinforcing polyester with sugarcane fibre (SCF) in AP-O can be a competitive to glass fibre. In conclusion, glass fibres have negative impact on the formation of polymer film and responsible for the observed discontinuous (ruptured) film for C-GRP composite. In other words, the back transfer polymer film formed at the interface managed to survive in the case of using SCF but in the case of GF, the effect of impact-type repeated loading caused by hard asperities and broken particles of glass fibre unstable the formation of such protective layers together with increased debonding and fractured fibre resulted in higher wear rate of C-GRP composite. Finally, microscopic observation evidenced that the SCF has the ability to have a fairly good bonding with the polyester matrix. This in turn made the separation of fibre from the composite more difficult and hence contributed to improvement of wear resistance for C-SCRP composite compared to C-GRP composite. In contrary, the bonding between GFs and the matrix for C-GRP composite was not that strong and the fibres were easily debonding.

Tribological studies of polyester reinforced with CSM 450-R-glass fiber sliding against smooth stainless steel counterface

Experimental investigations have been undertaken on chopped strand mat (CSM) 450-R-glass fiber reinforced polyester (CGRP) composite to study its tribological performance. Friction and wear tests were carried out using pin-on-disc configuration under dry sliding contact conditions. In the present work, tribological characteristics of CGRP composite were measured in three principal sliding directions relative to the chopped glass mat orientation in the composites. These are parallel direction (P), anti-parallel direction (AP), and normal direction (N). The effect of various experimental test parameters such as applied loads, sliding distances, and sliding speeds was studied. Scanning electron microscopy (SEM) is performed on worn surfaces to categorize the wear failure mechanisms. Friction and wear results are presented as a function of normal loads, sliding velocities, and sliding distances for P-, AP-, and N-orientations. The results of friction and wear, in general, are strongly influenced by all the test parameters. The highest wear rate is observed when sliding took place in N direction at all speeds tested (1.7, 2.8, and 3.9 m/s), about two orders of magnitude of AP and P directions. On the other hand, the lowest wear rate is exhibited when sliding took place in AP direction at higher speed level (2.8 and 3.9 m/s). At lower speed, (1.1, 1.7, and 2.2 m/s) P-orientation gave lower wear rate. The normal orientation shows 25–55% higher friction coefficients than those obtained for other orientations, i.e. P and AP. Although the sliding took place against smooth stainless steel counterface, the SEM microphotographs showed various mechanisms of abrasive wear nature, i.e. fiber fracture, fragmentation, and peeling off, and microcrack initiation in the matrix and debris formation.

Study on Tribological Properties of Multi-walled Carbon Nanotubes/Epoxy Resin Nanocomposites

Multi-walled carbon nanotubes/epoxy resin (MWNTs/EP) nanocomposites with different MWNTs contents have been prepared successfully. The influence of MWNTs on the friction and wear behaviors of the nanocomposites was investigated by a friction and wear tester under dry-sliding contact conditions. The relative humidity of the air was about 50±10%. Contrast to pure EP, MWNTs/EP nanocomposites showed not only higher wear resistance but also smaller friction coefficient. MWNTs could dramatically reduce the friction and improve the wear resistance behaviors of the nanocomposites. The mechanisms of the significant improvements on the tribological properties of the MWNTs/EP nanocomposites were also discussed.