Sliding Wear Experiments Research Articles

Friction and wear characteristics of WC–Co cemented carbides in dry reciprocating sliding contact

Friction and wear properties of WC–Co cemented carbides with Co concentrations ranging from 6 up to 12 wt% and WC grain sizes in the sub-micrometer scale have been examined in reciprocating sliding wear experiments using a high-frequency TE77 pin-on-plate system. The aim of the work was to investigate the influence of test parameters such as normal contact force, oscillating velocity and sliding distance on the tribological characteristics. The tests were carried out under unlubricated conditions. The generated wear was quantified volumetrically by means of surface topography scanning measurements. The changes in test parameters gave a variation in wear of more than one order of magnitude. A marked increase in wear was seen as the load increased, whereas the friction coefficient displayed an opposite trend. Raising the oscillating speed was found to increase both friction coefficient and wear level. The wear tracks and wear debris were analyzed by scanning electron microscopy (SEM), energy disperse X-ray spectrometry (EDX) and X-ray diffraction (XRD). The observed mechanisms of wear are discussed with respect to the magnitude of wear that was measured.

Grain size–wear rate relationship for titanium in liquid nitrogen environment

This paper presents the results of sliding wear experiments conducted on high-purity titanium (Ti) against bearing-steel in liquid nitrogen (LN 2; boiling point: 77 K) environment. Ti samples of three different grain sizes (9, 17 and 37 μm) were used to study the effect of hardness, derived from grain refinement as well as cryogenic test temperature, on the wear properties of Ti. In our experiments, a constant load of 10 N and sliding speeds of 0.67, 1.11 and 4.19 m s −1 were used. The coefficient of friction (COF) for this tribo-couple varied between ∼0.25 and ∼0.50. While a steady state was always achieved, a peak in the COF was always noted in case of coarse-grain (37 μm) Ti tested at a sliding speed of 4.19 m s −1. Under the investigated sliding conditions, the wear rate was found to be of the order of 10 −3–10 −4 mm 3 N −1 m −1. The lowest wear rate was recorded in the fine-grain (9 μm) Ti at the highest sliding speed of 4.19 m s −1. The critical analysis of the worn surface topography reveals that the reduced wear rate was due to the formation of adherent and strain-hardened tribolayer. In order to show various dominant wear mechanisms of Ti, a qualitative map was developed in sliding speed–grain size space. Substructure evaluation revealed the formation of a dense array of deformation twins because of the plastic deformation, which often resulted in the subdivision of grains.

The effect of strontium on the microstructure and wear properties of A356–10%B 4C cast composites

This study was undertaken to investigate the effect of strontium (0.5%) as a modifier on the microstructure and dry sliding wear behavior of A356–10%B 4C particulate metal matrix composite (PMMC). The composite ingots were made by stir casting process. In this work, composite were characterized by scanning electron microscope equipped with energy dispersive spectrometer (EDS), and dry sliding wear experiment were performed in a pin-on-disc wear tester against a DIN 100Cr6 steel disc at speed of 0.5 ms −1 and normal loads of 20, 40 and 60 N. The obtained results showed that 0.5%Sr was needed to modify of silicon eutectic in A356–10%B 4C cast composite. Also, the wear results showed that the addition of strontium to MMCs can lead to reduction of wear rate through strong bonding (between B 4C and matrix) and silicon particle modification. Formation of compact transfer layer has been identified on the entire surface of the pins at the applied load of 60 N. It is suggested that the transfer layer which was formed under an applied load of 60 N can act as a protective layer and helps to reduce wear rate.

Investigations on the influence of graphite filler on dry sliding wear and abrasive wear behaviour of carbon fabric reinforced epoxy composites

In this experimental study, the dry sliding wear and two-body abrasive wear behaviour of graphite filled carbon fabric reinforced epoxy composites were investigated. Carbon fabric reinforced epoxy composite was used as a reference material. Sliding wear experiments were conducted using a pin-on-disc wear tester under dry contact condition. Mass loss was determined as a function of sliding velocity for loads of 25, 50, 75, and 100N at a constant sliding distance of 6000m. Two-body abrasive wear experiments were performed under multi-pass condition using silicon carbide (SiC) of 150 and 320 grit abrasive papers. The effects of abrading distance and different loads have been studied. Abrasive wear volume and specific wear rate as a function of applied normal load and abrading distance were also determined.The results show that in dry sliding wear situations, for increased load and sliding velocity, higher wear loss was recorded. The excellent wear characteristics were obtained with carbon-epoxy containing graphite as filler. Especially, 10wt.% of graphite in carbon-epoxy gave a low wear rate. A graphite surface film formed on the counterface was confirmed to be effective in improving the wear characteristics of graphite filled carbon-epoxy composites. In case of two-body abrasive wear, the wear volume increases with increasing load/abrading distance. Experimental results showed the type of counterface (hardened steel disc and SiC paper) material greatly influences the wear behaviour of the composites. Wear mechanisms of the composites were investigated using scanning electron microscopy. Wear of carbon-epoxy composite was found to be mainly due to a microcracking and fiber fracture mechanisms. It was found that the microcracking mechanism had been caused by progressive surface damage. Further, it was also noticed that carbon-epoxy composite wear is reduced to a greater extent by addition of the graphite filler, in which wear was dominated by microplowing/microcutting mechanisms instead of microcracking.

Influence of electrical discharge machining on the reciprocating sliding wear response of WC-Co cemented carbides

A number of commercially available WC-Co-based cemented carbides with 6 up to 12 wt.% Co were machined and surface finished by grinding as well as by wire electrical discharge machining (EDM) in demineralised water through a number of consecutive gradually finer EDM regimes. Comparative dry reciprocating sliding wear experiments on both wire-EDM and ground samples against WC-Co pins were conducted, using a pin-on-plate test rig, in order to investigate the influence of the EDM process on the tribological behavior. The worn surfaces of the investigated cemented carbides were scanned topographically and characterised by scanning electron microscopy (SEM). The post-mortem obtained wear volumes were compared to the online measured wear in order to determine correlations between wear volume and wear rate on the one hand and sliding distance on the other hand. The experimental results revealed a profound influence of surface finish conditions and distinctive EDM regimes on the wear behavior of WC-Co cemented carbides.

Tribology and cyclic oxidation behavior of plasma nitrided valve steel

In this study, the tribology and cyclic oxidation behavior of plasma nitrided DIN 1.4871 austenitic valve steel were investigated. For this purpose plasma nitriding treatments were carried out in nitrogen and hydrogen with ratio N 2/H 2: 1/3 at 10 Torr pressure. Nitriding cycles of 400, 450, 500 and 550 °C for 7 h were selected. To remove oxide layer and to enhance diffusion, an effective sputter cleaning procedure was applied in argon and hydrogen gases. The pin-on-disc sliding wear experiments were performed at a load of 6 N and sliding velocity of 0.1 m/s in normal atmosphere under dry condition. Cyclic oxidation tests used to evaluate the oxidation characteristics of the samples consisted of 50 cycles each 30 min at 750 °C. The structure and properties of the samples were examined by optical and scanning electron microscopy (SEM), microhardness measurements and X-ray diffraction. The results indicated plasma nitriding at all temperatures increased the wear resistance of valve steel when sliding against bearing steel. The 550 °C nitrided layer, with CrN, Fe 4N and Fe 2–3N on the surface, was most effective in improving wear resistance. In the case of cyclic oxidation, the results showed that oxidation resistance depends strongly on nitriding temperature. Nitriding at 450 °C produced a layer of predominantly “S” phase which was more effective in improving the oxidation resistance of valve steel.

Improvement of wear resistance of wire drawing rolls with Cr–Ni–B–Si + WC thermal spraying powders

In wire drawing process, wear of rolls must be considered because of wear that influences the economics of the forming process. In this study, a nickel based matrix reinforced with WC was deposited by low cost powder welding method on low carbon steel substrates in order to determine the wear resistance of wire drawing rolls. Powder welding method includes, contrary to plasma and high velocity oxyfuel (HVOF) spraying methods, the advantages such as the single operation of powder application-fusion, simplicity, cheapness, and the ease of application. Blends of NiCrBSi and WC powders were prepared in weight proportions of WC of 40%, 45%, 50%, 55%, and 60%, respectively. Wear performance of these coatings was investigated by the dry sliding wear experiments. The wear resistance of the metal matrix composite coatings is dependent on the amount of WC. From 40% to 60%, the increase of WC is very effective on the wear resistance. The coatings with 55% and 60% of WC were worn less than the other coatings. From 55% to 60%, further increase of WC was found not to be effective for the best wear resistance. The microscopic studies of WC particles and Ni-based matrix were characterized by the scanning electron microscopy (SEM). The SEM analysis on the worn surface of coated samples shows that the matrix is considerably worn while WC particles are not considerably worn at the beginning of the wear testing. Additionally, WC particles effectively provide protection for achievement of the wear resistance at advanced periods of the wear testing.

Effect of Normal Load and Sliding Velocity on Friction and Wear Behavior of Carbon Fiber Reinforced Epoxy Composites

Friction and dry sliding wear behavior of [0°/90°]S and unidirectionally (UD) oriented carbon-epoxy (C-E) composites has been studied using block-on-roller test set up. The dry sliding wear experiments were conducted for the following C-E composites namely 0°/90°, parallel and anti-parallel surfaces with respect to the sliding direction. The coefficient of friction and wear of the composites for two different loads and various sliding velocities have been determined. It was observed that the wear loss increases linearly with increase in sliding velocity/loads. Besides conventional weighing, determination of the coefficient of friction and examination of worn surface features by scanning electron microscopy (SEM) were undertaken to study the tribological behavior. Disorientation of fibers, fiber fracture, matrix deformation and wear debris damage mechanisms were observed under SEM. Composite wear was accompanied by material transfer onto the counter surface.

Edge Effects in Sliding Wear Behavior of ZrO<sub>2</sub>-WC Composites and WC-Co Cemented Carbides

A trend in the development of WC based cemented carbides and zirconia based ceramic composites is grain size refinement and more narrow grain size distributions of the starting powder, in order to accomplish higher hardness and abrasive wear resistance. The current work reports the results of dry sliding wear experiments on laboratory-made electrically conductive ZrO2-WC composites and commercially available WC-Co based cemented carbides, which have been manufactured and finished by rough cutting wire EDM with consecutive execution of gradually finer EDM regimes. Tribological data are obtained using a small-scale pin-on-plate test rig. Wear tracks are analyzed by surface scanning topography and scanning electron microscopy, revealing that the outer extensions of the wear tracks exhibit some differences in wear behavior compared to the central parts.

Wear depth model for thin tubes with supports

A wear depth prediction model is proposed for thin tubes worn by a contact with supports. It has the form of D ˙ = K w ˙ where D ˙ and w ˙ are the wear depth and the energy density rates, respectively; K is a wear coefficient with the unit of Pa −1. Two kinds of experiments, i.e. sliding and sliding/impact are conducted with the fuel rod tubes and the transversely concave-contoured supports under room temperature and air/water environments. The applied sliding amplitude was 50–100 μm and the contact normal force was 10–50 N in the sliding wear experiment. Impact force of around 30 N was applied in the sliding/impact wear experiment. It was found that a linearity between D ˙ and w ˙ exists at the same contact normal force condition. In the sliding wear experiments, K is larger in the air than in the water environment. It was verified that the addition of an impact is detrimental to a wear failure than a sliding wear only. It is thought that K can represent a wear resistance parameter in the point of the wear depth when the wear mechanism is similar. The influence of wear debris dispersion behaviour on the present model is discussed.

EFFECT OF HOT DEFORMATION ON THE TRIBOLOGICAL BEHAVIOUR OF Ti-6Al-4V ALLOY

The present work investigates the effect of both linear velocity and applied stress parameters on the mechanical wear behaviour of hot forged Ti-6Al-4V alloy at room temperature. A hot upset forging process was carried out between 1000 and 950°C to refine the as-cast structure and consequently to improve the tribological behaviour of the material under dry sliding wear. Numerous dry sliding wear experiments were carried out on a tool steel disc with an applied stress (varied between 0.2 and 2.0 MPa). The sliding linear velocity was varied between 1250 and 8677 mm/s. An X-ray diffraction analyses as well as a scanning electron microscope investigation were carried out after wear tests on the surfaces of the worn specimens in order to characterize the nature of the oxidized surfaces and explore the surface tribology at different levels of wear velocities and different applied stresses.Le présent travail étudie l’effet de la vélocité linéaire et des paramètres de contrainte appliquée sur le comportement d’usure mécanique à la température de la pièce de l’alliage Ti-6Al-4V forgé à chaud. On a effectué un procédé de refoulage à chaud entre 1000 et 950 °C afin d’affiner la structure de coulée et conséquemment d’améliorer le comportement tribologique du matériau sous condition d’usure par glissement à sec. On a effectué de nombreuses expériences d’usure par glissement à sec avec un acier à outil en forme de disque avec une contrainte appliquée (variant entre 0.2 et 2.0 MPa). La vélocité de glissement linéaire variait entre 1250 et 8677 mm/s. On a effectué des analyses de diffraction des rayons x ainsi qu’une investigation par microscope électronique à balayage après les épreuves d’usure sur la surface des spécimens usés afin de caractériser la nature des surfaces oxydées et d’explorer la tribologie de surface à différents niveaux de vitesse d’usures et différentes contraintes appliquées.

The effect of H2/C2H2 ratio on the structure and tribological properties of carbon thin films prepared by PBII

Carbon thin films have been prepared on Si by plasma-based ion implantation (PBII) with H2 and C2H2 mixed gases with various H2/C2H2 ratios. The effect of the H2/C2H2 ratio on the structure and tribological properties of the thin films has been investigated. XPS composition depth profile shows that a H2/C2H2 ratio of about 1.0 corresponds to the just appearance of a carbon film growing on a C–Si transition layer showing gradually compositional and structural changes between the carbon film and the substrate, and above the ratio of 1.0 corresponds to no carbon film but a carbon-implanted layer. As the H2/C2H2 ratio increases, the carbon film shows the rapidly decreasing thickness. Raman spectra show that the carbon films are diamond-like carbon (DLC) films rich in Sp3 bonds carbons. A H2/C2H2 ratio of approximately 0.1 corresponds to the maximal Sp3/Sp2 ratio. The H2/C2H2 ratio in the range of 0–0.3 corresponds to larger Sp3/Sp2 ratio than the ratio of 0 (without H2 additive). AFM morphologies exhibit that the DLC films are smooth and compact, and the H2/C2H2 ratio of 0.08 corresponds to the smallest roughness. On the other hand, ball-on-disk sliding wear experiments show that the H2/C2H2 ratio of 0–0.15 exhibit more significant improvement in tribological properties of the DLC films than the ratio of 0. In particular, at low sliding load of below 0.5 N the DLC films present more than 3 h-wear life and near to zero-wear rate. It is found that the H2/C2H2 ratio of about 0.08 corresponds to the best tribological properties. The influences of sliding load, sliding frequency, film thickness and counter-ball materials on the tribological properties are also presented.

Wear mechanism of Ni–P–BN(h) composite autocatalytic coatings

Sliding wear experiments at room temperature were performed, using a pin-on-disc configuration, in order to study the wear mechanism of autocatalytic composite Ni–P–BN(h) coatings deposited on AISI 316L stainless steel against AISI 52100 steel balls. Coatings with 11, 35, 45 and 67 vol.% BN(h) were obtained by dispersing the BN(h) of an average particle size of 5.16 μm in a sodium hypophosphite based autocatalytic bath with enhanced agitation and surfactant addition. Scanning Electron Microscopy and 3D perfilometry techniques were employed to study the wear scars. Knoop microhardness, roughness, friction coefficients and wear resistance of the coatings for all experimental conditions are also reported. The results obtained indicate that, in the case of coatings with BN(h) content higher than 11 vol.%, the wear mechanism is a mild adhesive wear mechanism (adhesive ploughing) with high plastic strain of the coatings and low coating transfer to the ball. Coatings with 11 vol.% BN(h) show a mixed mechanism of adhesive and abrasive wear.

Tribological characteristics of CrCN coatings at elevated temperature

Dry sliding wear experiments at specific temperatures ranging from 20 to 500 °C were conducted on CrCN coatings deposited onto steel substrates. The coatings were worn against 100Cr6 bearing steel balls, Si 3N 4 and Al 2O 3 balls, using a pin-on-disc sliding configuration at a contact load of 5 N. Friction coefficient and coating wear rates were measured, and wear tracks were analysed using SEM equipped with EDX. Coatings exhibited good wear performance and unexpected behaviour at elevated temperatures.

Effects of Contact on the Abrasiveness of a Thin Boron Carbide Coating

Boron carbide (B4C) has been studied under dry sliding conditions for use as a potential finite-life run-in coating. Such a coating has been found to polish its mating surface during dry sliding wear, thereby providing fatigue resistance to the coated part. Employing such run-in coatings requires a complete understanding of the changes that occur in the coating abrasiveness during the polishing process. Therefore, a thorough understanding of the changes in the contact conditions of such a system needs to be obtained. This study presents the role that contact plays in changes of the overall coating abrasiveness. By performing sliding wear experiments using various contact conditions, i.e. ball-on-disc, pin-on-disc and cone-on-disc, we directly investigated the effects of macro-scale contact conditions on the coating abrasiveness. It was found that the rate at which the coating abrasiveness decreased was independent of the macro-scale contact conditions. These findings were further validated by investigating the coating abrasiveness results that were obtained by performing spiral track wear experiments. Through the use of a three-dimensional thermomechanical asperity contact model, it was found that the coating abrasiveness was controlled by the actual micro-scale contact conditions. This study supports the classic Greenwood–Williamson model, which states that the number of micro-scale contacts and the total actual area of contact remains constant for a given load.

Structures and tribological properties of diamond-like carbon films prepared by plasma-based ion implantation on Si

DLC films ranging from 5 to 180 nm in thickness have been prepared by plasma-based ion implantation (PBII) with C on Si. The structures of the films were studied with XPS and Raman spectroscopy. The nanohardness and the intrinsic stress of the films were measured. Dry sliding wear experiments have been carried out, using a ball-on-disc tester, to investigate the tribological properties of DLC films against alumina balls, employing various normal applied loads and reciprocating frequencies. For comparison, DLC films prepared by plasma-assisted chemical vapor deposition (PACVD) on Si were also investigated. The results show that the films prepared by PBII exhibit more significant improvement in tribological properties than the films prepared by PACVD because the former present higher sp 3/sp 2 ratio, higher hardness and lower stress than the latter. The effects of the film thickness, the applied loads and the reciprocating frequencies on the tribological properties are also presented.

Cumulative Damage Rule under Two-Step Sliding Wear of White Metal

Sliding wear experiments were performed under two-step compressive loading in order to clarify the effect of load fluctuation on the wear life of the white metal bearing. Cumulative damag under two-step wear experiment cannot be predicted by a linear damage rule, since it is affected by the load sequence. The value of cumultive damage is less than unity in the high-low test, on the other hand in the low-high test the reverse is true. The constitutive equation for the wear test was proposed.The equation is capable to predict wear lives under constant loading as well as wear damages in the two-step sliding wear experiment.

Tribological behavior of Ti–Si–N coating layers prepared by a hybrid system of arc ion plating and sputtering techniques

Ti–Si–N coating layers were deposited onto WC–Co substrates by a hybrid system of arc ion plating and sputtering. The coating layers were prepared with different Si contents to investigate the effect of Si content on their tribological behaviors. For this study, the dry sliding wear experiments were conducted on Ti–Si–N-coated WC–Co discs at three different sliding speeds, 0.1, 0.3, 0.5 m/s, against steel (SUJ2) and alumina balls using a conventional ball-on-disc sliding wear apparatus. In the case of steel ball, the average friction coefficient slightly decreased with increasing the sliding speed regardless of Si content, due to adhesive wear behavior between coating layer and steel ball. At constant sliding speed, the average friction coefficient decreased with increase of Si content. This behavior was attributed to the formation of self-lubricating tribo-layers such as SiO 2 or Si(OH) 2. Conversely, in the case of the alumina ball, the average friction coefficient increased with increasing sliding speed regardless of Si content, indicating that the abrasive wear behavior was more dominant when the coating layers slid against an alumina ball. From our experimental results, it was found that the tribological behavior of Ti–Si–N coating layers was affected by factors such as Si content, sliding speed, and type of counterpart materials.

Environment effects on the reciprocating wear of Inconel 690 steam generator tubes

Reciprocating sliding wear experiments have been performed in various environmental conditions, such as various temperatures, air and water environments to examine the wear properties of Inconel 690 steam generator (S/G) tubes. For present study, the test rig was designed to examine the reciprocating and rolling wear properties in high temperature. The test rig consists of pressure vessel, electric heater, reciprocating, rolling and loading units. Tests were performed at constant applied load and sliding distance to investigate the effects of temperature and environment. Then, the worn surfaces were observed using scanning electron microscope to investigate the wear mechanism. In water environment, the wear loss increased with temperature between 25 and 150 °C. Beyond 150 °C, the loss decreased with increasing temperature. However, in air environment, the loss decreased with increasing temperature in all temperature ranges. The wear loss variation with temperature was due to the formation of oxide layer. It was assumed that the layer was formed by wear debris sintering, cold welding or oxidation mechanisms and these properties were varied with tests temperatures and environments, which was confirmed by identification of the oxide layer by worn surface observation.

Assessment of wear performance of flame sprayed and fused Ni-based coatings

Characterization of the flame sprayed and furnace fused NiCrBSiC alloy coatings with two different carbon contents and 15–45 wt.% WCCo addition is described in terms of microstructure, microhardness and differential thermal analysis. Microstructural development of these coatings before and after fusing treatment is discussed to identify the precipitates in the coatings. Optimum fusing conditions (time and temperature) for wear-testing sample were investigated in terms of microhardness and porosity of the coatings. Wear performance of these coatings was also investigated by two- and three-body abrasive and dry sliding wear experiments. The coating of 35% WC with NiCrBSiC is showing the best quality (the highest hardness and the lowest porosity). However, 25% WC addition is showing the best wear resistance for Sugaru abrasive wear test, while 40% WC addition is showing the best wear resistance for DSRW (dry sand rubber wheel) abrasive wear test. It is also shown that the dry sliding wear resistance of the 20% (and/or 30%) WCNiCrBSiC composite coating is almost 10 times better than that of the quenched and tempered JIS SUJ2 bearing steel.