Friction and wear characteristics of ZDDP in the sliding of steel against aluminum alloy

The tribological properties of zinc dialkyldithiophosphate (ZDDP) antiwear additives in the sliding of steel against aluminum alloy were investigated by an oscillating friction and wear apparatus, an Optimol SRV tester. It was found that ZDDP produced larger wear of aluminum alloy than base stock, especially at high concentration. The acting mechanism of ZDDP in the lubricated aluminum-on-steel system was proposed.     

Dry sliding wear response of some industrial powder coatings

This investigation analyses the sliding wear response of polyester and polyphthalamide powder coatings deposited by electrostatic spraying and ‘hot dipping’ fluidised bed. Tribological tests were conducted under dry conditions in a pin-on-disc arrangement, using a spherical counterpart. The experimental results showed that the deposition technology, the coating material and the thickness of the coating play key roles in determining the wear response of powder coatings. In particular, polyester coatings are deposited by a fluidised bed offer superior wear endurance, along with a low abrasion volume and a low wear rate. Conversely, polyphthalamide coatings are susceptible to faster wear by local cutting and plastic fatigue mechanisms.     

Unlubricated sliding and rolling wear of thermoplastic dynamic vulcanizates (Santoprene) against steel

The friction, sliding and rolling wear characteristics of thermoplastic dynamic vulcanizates (TPV; Santoprene^® grades), composed of polypropylene (PP), ethylene/propylene/diene rubber (EPDM) and extender oil, were studied against steel counterparts in dry condition. The composition and basic mechanical properties of the TPV of various hardness (Shore A = 60°, 70° and 80°) were evaluated. The wear performance of the TPVs was investigated in different tribotests, viz. pin-on-plate (POP), cylinder-on-plate (fretting) and rolling ball-on-plate (RBOP), whereby “plate” was always the rubber. From the above tests the coefficient of friction (COF) and specific wear rate were determined. It was established that with increasing hardness usually both COF and the specific wear rate were reduced. Values of the COF and wear rate depended strongly on the configuration and testing parameters of the related tribotests. The wear mechanisms were concluded by inspecting the worn surfaces by white light profilometry and scanning electron microscopy (SEM), respectively, and discussed.     

Friction and wear of blended polyoxymethylene sliding against coated steel plates

Measurements were made of the dynamic friction coefficients and specific wear rates of several thermoplastics rubbing against relatively soft coatings on steel plates. Polyoxymethylene (POM)-based composites were investigated using reciprocating, line contact tests against two types of corrosion-protected steel plates (electro-deposited cathodic epoxy layers, called “E-coatings”, and galvanised plates). In addition to virgin POM, composites containing glass fibres, polytetrafluoroethylene (PTFE) fibres, PTFE micro-powder, and high-viscosity silicon oil were investigated. Sliding speeds ranged from 0.05 to 0.3 m/s, and normal loads ranged from 5 to 30 N. The E-coating failed at high loads and velocities. The beneficial effects of lubricating additives in tests with uncoated steel counterfaces were also observed with the coated steel surfaces. POM with glass fibre additives was found to be more abrasive than the base material. The considered non-conformal contact produced similar friction and wear trends than those obtained for the conformal contact.     

Influence of ball burnishing on surface quality and tribological characteristics of polymers under dry sliding conditions

In this paper, the application of ball burnishing as a new surface treatment process for polymers is investigated. The polymers used were polyoxymethylene (POM) and polyurethane (PUR). The lowest surface roughness value achieved for POM was 0.44 μm (45% decrease) and for PUR was 0.46 μm (42% decrease). The lowest coefficient of friction value achieved was 0.22 (32.9% decrease) for POM and 0.24 (28.8% decrease) for PUR. The lowest specific wear rate value achieved was 0.31×10⁻⁶ mm³/N m (38.6% decrease) for POM and 0.41×10⁻⁶ mm³/N m (37.9% decrease) for PUR.     

Effect of temperature on friction and wear of prehardened tool steel during sliding against 22MnB5 steel

Abstract

Mechanical components in tribological systems exposed to elevated temperatures are gaining increased attention since more and more systems are designed to operate under extreme conditions. In hot metal forming, the effect of temperature on friction and wear is especially important since it is directly related to process economy (tool wear) and quality of the produced parts (friction between tool and workpiece). This study is therefore focused on fundamental understanding pertaining to the tribological characteristics of prehardened hot work tool steel during sliding against 22MnB5 boron steel. The tribological tests were carried out using a high temperature reciprocating sliding friction and wear tester under a normal load of 31 N (corresponding to a contact pressure of 10 MPa), a sliding speed of 0·2 m s^?1 and temperatures ranging from 40°C to 800°C. It was found that friction coefficient and specific wear rate decreased at elevated temperature because of formation of compacted wear debris layers on the surfaces.     

Friction, wear and material transfer of sintered polyimides sliding against various steel and diamond-like carbon coated surfaces

Polyimide cylinders are slid under 50 N normal load and 0.3 m/s sliding velocity against carbon steel (R_a=0.2 and 0.05 μm), high-alloy steel (R_a=0.05 μm), diamond-like carbon (DLC, R_a=0.05 μm) and diamond-like nanocomposite (DLN, R_a=0.05 μm). Only for a limited range of test parameters, the friction of polyimide/DLN is lower than for polyimide/steel, while polyimide shows higher wear rates after sliding against DLN compared to steel counterfaces. The DLN coating shows slight wear scratches, although less severe than on DLC-coatings that are worn through thermal degradation. Therefore, also friction against DLC-coatings is high and unstable. Calculated bulk temperatures for steel and DLN under mild sliding conditions remain below the polyimide transition temperature of 180 °C so that other surface characteristics explain low friction on DLN counterfaces, as surface energy, structural compatibility and transfer behaviour. Friction is initially determined through adhesion and it is demonstrated that higher surface energy provides higher friction. After certain sliding time, different polyimide transfer on each counterface governs the tribological performance. Polyimide and amorphous DLC structures are characterised by C–C bonds, showing high structural compatibility and easy adherence of wear debris on the coating. However, it consists of plate-like transfer particles that act as abrasives and deteriorate the polyimide wear resistance. In sliding experiments with high-alloy steel, wear debris is washed out of the contact zone without formation of a transfer film. Transfer consists of island-like particles for smooth carbon steel and it forms a more homogeneous transfer film on rough carbon steel. The latter thick and protective film is favourable for low wear rates; however, it causes higher friction than smooth counterfaces.     

Artificial neural networks for predicting sliding friction and wear properties of polyphenylene sulfide composites

In this paper the potential of using artificial neural networks (ANNs) for the prediction of sliding friction and wear properties of polymer composites was explored using a newly measured dataset of 124 independent pin-on-disk sliding wear tests of polyphenylene sulfide (PPS) matrix composites. The ANN prediction profiles for the characteristic tribological properties exhibited very good agreement with the measured results demonstrating that a well trained network had been created. The data from an independent validation test series indicated that the trained neural network possessed enough generalization capability to predict input data that were different from the original training dataset.     

High-temperature friction and wear behaviour of different tool steels during sliding against Al–Si-coated high-strength steel

The recent years have witnessed an increasing usage of high-strength steels as structural reinforcements and in energy-absorbing systems in automobile applications due to their favourable high-strength-to-weight ratios. Owing to poor formability, complex-shaped high-strength steel components are invariably produced through hot-metal forming. The high-strength steel sheets are in some instances used with an Al–Si-coating with a view to prevent scaling of components during hot-metal forming. However, friction and wear characteristics of Al–Si-coated high-strength steel during interaction with different tool steels have not yet been investigated. With this in view, friction and wear behaviours of different tool steels sliding against Al–Si-coated high-strength steel at elevated temperatures have been investigated by using a high-temperature version of the Optimol SRV reciprocating friction and wear tester at temperatures of 40, 400 and 800 °C. In these studies both temperature ramp tests with continuously increasing temperature from 40 to 800 °C and constant temperature tests at 40, 400 and 800 °C, have been conducted. The results have shown that both the friction and wear of tool steel/Al–Si-coated high-strength steel pairs are temperature dependent. Friction decreased with increasing temperature whereas wear of the tool steel increased with temperature. On the other hand, the Al–Si-coated high-strength steel showed significantly lower wear rates at 800 °C as compared to those at 40 and 400 °C. The Al–Si-coated surface undergoes some interesting morphological changes when exposed to elevated temperatures and these changes may affect the friction and wear characteristics. The mechanisms of these changes and their influence on the tribological process are unclear and further studies are necessary to fully explain these mechanisms.     

Friction and wear characteristics of steel on rock under water and oil based lubricated sliding conditions

Abstract

In recent years, drilling extended reach wells have become more and more common in the petroleum industry to optimise the oil and gas production. Extended reach wells are defined as wells that have two times more horizontal step out than true vertical depth. High friction (frictional torque) and drag are two of the mechanical limiting factors while drilling longer horizontal wellbores. There are numerous methods and tools developed to lower the drillstring friction. Drilling non-circular wellbores is a new concept with potential to minimise the mechanical friction by reducing drillstring and sidewalls contact area. However, this will cause an increase of contact pressure owing to the reduced contact area between drillstring and the formation. This article presents results obtained from an experimental study pertaining to the friction behaviour using a pin on disc set-up with steel pin and granite disc in the presence of water and oil based lubricants. These tests have been designed to represent frictional contact conditions between a rotating steel drillstring and the wellbore wall at different contact pressures. Test results show that the friction coefficient decreases with an increase of contact pressure in wet condition for both water and oil based lubricants. It is also observed that the friction factor increased by adding sand and phyllite particles to the water based lubricant. Considering the wear scars, the friction coefficient shows reduction with increased contact pressure in all tests with and without particles for both water and oil based lubricants.     

Effect of quartzite and granite in wear surfaces on dry sliding

Abstract

The wear surfaces abraded with quartzite and granite were subjected to scratch tests. Sharp and blunt indenters were used with various constant loads to produce controlled abrasive wear tracks. The characteristics of deformation mechanisms and material removal were further studied using a scanning electron microscope to determine the differences in the tribological behaviour between the quartzite and granite wear surfaces.

The results indicate that quartzite residues are more uniformly distributed as individual particles on the wear surfaces and therefore provide more stable frictional forces. In the case of granite the abrasive residues are rather non-uniformly collected into piles of abrasives.     

Friction and wear behavior of pure carbon strip sliding against copper contact wire under AC passage at high speeds

A series of tests on the friction and wear behaviour of pure carbon strip/copper contact wire with alternating current were conducted on a ring-on-block sliding tester at a high speed. The electric current, normal force and sliding velocity have distinct effects on the test results. The worn scar has the smallest size without electric current. The worn scar becomes larger with increasing electric current. Arc ablation pits, dark stream-lines of arc ablation, slipping marks, spalling blocks and the copper-like layer are found on the worn surfaces. Arc erosion, abrasive wear and adhesive wear are main wear mechanisms.     

Friction and wear behaviour of stainless steel rubbing against copper-impregnated metallized carbon

A series of experimental tests were carried out using stainless steel rubbing against copper-impregnated metallized carbon under electrical current on a pin-on-disc test rig. The test parameters include the sliding speed of 60-100 km/h, normal force of 40-80 N and electrical current of 0-50 A. During testing, the friction coefficient and wear volume were recorded. The topography of worn surfaces was also observed with SEM. The cross sectional profiles of worn surfaces of stainless steel were measured with Ambios profiler. The result displays that electrical current, normal load and sliding speed have a distinct effect on the friction and wear behaviour of stainless steel rubbing against copper-impregnated metallized carbon. Without electric current, the friction coefficient is largest but the wear volume of copper-impregnated metallized carbon is lowest. With increasing electric current, the friction coefficient decreases while the wear volume of copper-impregnated metallized carbon increases. Through the whole test, it is found that the wear loss of stainless steel was light. The wear of copper-impregnated metallized carbon becomes severe when electrical current or sliding speed is high. When the electrical current or sliding speed is high, arc ablation is a dominant wear mechanism of copper-impregnated metallized carbon.     

Dry sliding wear of epoxy/cenosphere syntactic foams

Dry sliding wear behavior of epoxy matrix syntactic foams filled with 20, 40 and 60 wt% fly ash cenosphere is reported based on response surface methodology. Empirical models are constructed and validated based on analysis of variance. Results show that syntactic foams have higher wear resistance than the matrix resin. Among the parameters studied, the applied normal load (F) had a prominent effect on wear rate, specific wear rate (w_s) and coefficient of friction (μ). With increasing F, the wear rate increased, whereas w_s and μ decreased. With increase in filler content, the wear rate and w_s decreased, while the μ increased. With increase in sliding velocity as well as sliding distance, the wear rate and w_s show decreasing trends. Microscopy revealed broken cenospheres forming debris and extensive deformation marks on the wear surface.     

Friction and wear response of nitride coating deposited through PVD magnetron sputtering

Surface engineering with applied coating plays a vital role in any industrial application. These coatings are meant for better mechanical and tribological characteristics when applied on to the materials. The major challenge in selecting a suitable coating strategy is their input process parameters. There are several parameters which influences the coating properties, but it is hard to choose one of them and ignoring others. Multilayers of tungsten nitride are attracting great interest to modulate their tribological and mechanical properties through physical vapour deposition process due to their wide application range. These multilayer nitride films were deposited through unbalanced reactive magnetron sputtering technique. The tribological tests were performed on a pin-on-disc tribometer at room temperature and it has been observed that friction and wear values reduce drastically while applying multilayer coatings. Later, artificial neural network (ANN) is employed to optimize the tribological properties of sputtered coatings.     

Friction and dry sliding wear of bismaleimide filled with carbon nanotubes

Three types of bismaleimide–carbon nanotubes (CNTs) nanocomposites were fabricated using two types of original multiwalled CNTs with different diameters and one amide functionalized CNTs. The influence of diameter, content and functionalization of CNTs on the flexural and dry sliding wear behaviour were measured with universal testing machine and pin-on-disc wear apparatus. The experimental results indicated that at 1.5 wt-%, the bismaleimide-functionalized MWCNTs exhibited highest flexural strength of 156 MPa which is increased by 164% as compared to the neat matrix, and lowest specific wear rate of 1.8 × 10^?4 mm³ N^?1 m^?1 which is decreased by 90% as compared to the neat matrix. This was attributed to the dispersion of CNTs in the matrix and the filler-matrix adhesion and internal strength of the composite.     

Effect of Molecular Structure on Friction and Wear of Polymer Thin Films Deposited on Si Surface

In this study, the influence of the molecular structure (linear or with bulky side groups) of polymer films covalently attached to Si surface on tribological properties is investigated. Two polymers, PE (polyethylene) and PS (polystyrene), are selected where PE has simple linear molecular structure whereas PS has linear molecular structure but contains bulky benzene groups located at the sides of the linear chain. PE and PS molecules, both with reactive maleic anhydride groups, are chemisorbed onto Si via an intermediate APTMS SAM (3-aminopropyltrimethoxysilane self-assembled monolayer). Water contact angle measurements, AFM (atomic force microscopy), ellipsometry, and XPS (X-ray photoelectron spectroscopy) are used to identify and characterize the polymer films. Tribological properties are studied using a microtribometer where a 4 mm diameter Si₃N₄ ball is used as the counterface. Among the two polymer films investigated, Si/APTMS/PE has shown very low coefficient of friction (0.08) and high wear life (∼4,400 cycles) than those of Si/APTMS/PS. Surprisingly, Si/APTMS/PS did not show any improvement in tribological properties when compared to that of bare Si. The present study proves that the polymer with linear molecular structure without the bulky side groups show good tribological properties even when it is coated as a thin film and hence such polymers can be used as thin-films for reducing friction and wear of substrates such as Si or other materials.     

Friction and wear performances of brake material dry sliding against a composite with a semi-interpenetrating network structure of ceramics and Al-alloy

The friction and wear performances of brake material dry sliding against semi-interpenetrating network ceramics/Al-alloy composites were determined using a SRV testing machine. For applied loads from 40-160 N, the friction decreased at 100 and 250 °C. The former friction was superior to the latter. Wear increased at 100 °C but decreased at 250 °C, and converged gradually in both cases. Friction fade took place at high temperatures, followed by overrecovery upon cooling. Higher temperatures increased wear. The proposed friction models incorporated with scanning electron microscopy and energy dispersive X-ray analysis explain the test results better.     

Effect of matrix morphology on the wear and friction behavior of alumina nanoparticle/poly(ethylene) terephthalate composites

The friction and wear properties of poly(ethylene) terephthalate (PET) filled with alumina nanoparticles were studied. The nanoparticle loading was varied from 1 to 10 wt.%. The nanocomposite samples were tested in dry sliding against a steel counterface. The results show that the addition of nanoparticles can increase the wear resistance by nearly 2× over the unfilled polymer. The average coefficient of friction also decreased in many cases. The nanocomposites form a more adherent transfer film that protects the sample from the steel counterface, although the presence of an optimum filler content may be due to the development of abrasive agglomerates within the transfer films in the higher wt.% samples. This study varied both crystallinity and weight percent of filler in a PET matrix in an attempt to separate the effects of nanofillers and crystallinity on the tribology.     

The role of triboparticulates in dry sliding wear

In this paper, wear processes and mechanisms for wear transitions with sliding time and temperature during sliding of a nickel-based alloy, N80A, in oxygen at temperatures to 250°C are discussed. Transitions in wear from high rates to low rates with sliding time were always observed at all the temperatures investigated. The transitions in wear were usually accompanied by transitions in contact resistance between the rubbing surfaces from nearly zero to positive high values. It was found that wear debris particles were heavily involved in the wear processes. The transitions in wear and contact resistance with sliding time mainly resulted from the development of wear-protective layers following the compaction of wear debris particles on the rubbing surfaces. The adhesion of triboparticulates to each other and to the rubbing surfaces played an important role in the rapid decrease in wear rate with sliding time and with increase in temperature. Processes involved in the development of the wear-protective particle layers and mechanisms for the wear transitions have been described on the basis of experimental observations. The importance of triboparticulates in wear and its implications for wear protection are discussed.