Water-lubricated Conditions Research Articles

Friction and wear behavior of different seal materials under water-lubricated conditions

The shaft mechanical face seal in a high-speed turbopump of a liquid rocket engine often operates under extremely harsh conditions. For example, a low-temperature and low-viscosity fluid (such as liquid oxygen or liquid hydrogen) is used as a lubricant. The performance of the seal rings, especially the friction and wear behavior, directly determines whether the seal functions normal. In this study, the friction and wear behavior of several ring materials are tested using a pin-on-disk tribo-tester, and the wear morphology of the ring is investigated. The friction coefficients (COFs) and mass-wear rates under dry-friction and water-lubricated conditions, which are used to simulate low-viscosity conditions, are obtained. The results show that at a pressure-velocity (PV) value of 2.4 MPa·(m/s), the COF between the copper graphite (stator) and copper-chrome alloy disk (rotor) is low (with a value of 0.18) under the dry-friction conditions, and the 5-min wear mass of the copper graphite is approximately 2 mg. Under the water-lubricated conditions, compared with other materials (such as copper-chrome alloy, S07 steel, alumina ceramic coating, and nickel-based calcium fluoride), the S07 steel with a diamond-like carbon film is preferred for use in a high-speed turbopump under extreme conditions. The results of this study can provide theoretical and experimental guidance in the design of mechanical face seals in liquid rocket engines.

Tribological and physical properties of PTFE-NBR self-lubricating composites under water lubrication

PurposeThis paper aims to explore the possibility of converting the nitrile butadiene rubber (NBR) water-lubricated bearing material into a self-lubricating bearing material by the action of polytetrafluoroethylene (PTFE) particles and water lubrication.Design/methodology/approachA group of experimental studies was carried out on a ring-on-block friction test. The physical properties, tribological properties and interface structure of PTFE-NBR self-lubricating composites filled with different percentages of PTFE particles were investigated.FindingsThe experimental results indicated that the reduction in friction and wear is a result of the formation of the lubricating film on the surface of the composites. The lubricating film was formed of a large amount of PTFE particles continuously supplied under water lubrication conditions and the PTFE particles here can greatly enhance the load capacity and lubrication performance.Originality/valueIn this study, the tribological properties of PTFE particles added to the NBR water-lubricated bearing materials under water lubrication were investigated experimentally, and the research was carried out by a ring-on-block friction test. It is believed that this study can provide some guidance for the application of PTFE-NBR self-lubricating.Peer reviewThe peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-05-2020-0187/

Anti-corrosion and corrosive wear properties of AISI 316L stainless steel with surface nanocrystallization by surface mechanical rolling treatment

In this work, surface mechanical rolling treatment (SMRT) was adopted to obtain the gradient nanostructured (GNS) layer on AISI 316L stainless steel (SS) surface. To evaluate the effect of the GNS, anti-corrosion and corrosive wear tests of the SMRT sample were conducted in pure water and corrosive medium in comparison with a unSMRT (i.e., coarse-grained 316L SS). The corrosion behaviors, tribological properties, damage mechanism as well as relation of pitting and delamination, have been investigated to clarify their synergetic effects and failure mechanism. The results show that, the GNS of 316L SS has poor corrosion resistance due to initiation in local of stress corrosion crack (SCC). However, in comparison with the unSMRT sample, the pitting resistance of 316L SS after SMRT is significantly enhanced. For both samples, the wear loss by delamination is obviously accelerated by corrosion in the friction process. The tribo-corrosion resistance is markedly enhanced with the GNS layer relative to the unSMRT sample, the GNS layer can effectively inhibit the formation of delamination in the corrosive environment, and can also mitigate the abrasive wear in the water lubrication condition, due to the beneficial combination of superfine nanocrystalline structure and high hardness of the GNS layer.

Effect of particle concentration on the tribological properties of NBR sealing pairs under contaminated water lubrication conditions

The abrasive wear behavior of elastomers has attracted a lot of attention and interest in order to better comprehend its effect on the service performance of the fluid sealing pairs. The objective of this work was to study the tribological performance of the fluid sealing pairs under various abrasive concentration conditions. Therefore, this study developed an abrasive wear test experiment for an acrylonitrile–butadiene rubber (NBR) cylinder against 316L stainless steel plate tribo-pairs to evaluate reciprocating sliding tests under different particle concentrations.Results demonstrate that the abrasives feature strong aggressivity, which impedes the formation of a good friction-reduction water film, results in weak lubrication, changes the friction coefficient and wear rate, and deteriorates the tribological performance of the tribo-pairs. The friction coefficients of the low abrasive concentration are relatively small, and the friction coefficient increases with increasing abrasive concentration.At different abrasive concentrations and sizes, the rubber matrix is attacked in various forms by the hard particles, which appear as pinning, particle agglomeration embedment, and abrasive flow erosion. Particle concentration affects the damage behavior of the tribo-pairs, and the particles easily enter the interface of the tribo-pairs when their concentration is high.

Experimental measurement on friction performance of PDC bearings for oil drilling under different working conditions

Abstract As a kind of superhard material, the polycrystalline diamond compact (PDC) has been extensively used in engineering with its high strength and high wear resistance. Meanwhile, PDC has been increasingly used in bearing design to improve bearing capacity and service life. However, as a bearing material, its friction coefficient under different working conditions is not clear although it is a very important parameter. In this paper, the authors proposed a theoretical model of friction measurement and design a set of measurement rig to investigate the friction characteristics of the PDC bearing. The measurement equipment is developed based on the Coulomb friction model, with the three measurement environments taken into consideration: dry, water and drilling mud. A pair of thrust ball bearing was used in the measurement equipment to equilibrium axial load. But the friction coefficient of thrust ball bearing is proved far less than that of the PDC bearing in the experiment. The frictional coefficient of PDC bearings can be stabilized at about 0.12 under dry friction or water lubrication conditions and increase to 0.2 when tested under drilling fluid environment. Measuring the friction coefficient of PDC bearing -especially under drilling fluid environment can not only provide support for the design of the downhole tool where the bearing friction coefficient obviously affects the feasibility and agility of the tool but also help people to deepen the understanding of PDC materials.

Wetting and tribological properties of superhydrophobic aluminum surfaces with different water adhesion

In this article, a facile and efficient nanosecond laser processing method was carried out to construct a grid of microgrooves on an aluminum surface. After modification with low surface energy materials, various superhydrophobic surfaces with different water adhesion are obtained. The wetting properties of the obtained samples could be regulated by adjusting the number and line spacing (LS) of laser processing steps. The contact angle of the obtained superhydrophobic samples increased with the decrease in LS, while the sliding angle showed the opposite trend. Increasing the number of laser processing steps is beneficial to increase the contact angle and reduce the sliding angle. The wetting mechanism was analyzed to explain the cause of change in the wetting behaviors. The tribological tests showed that the surface textures of superhydrophobic samples improved their tribological properties. What is more, whether it is under dry friction or water lubrication conditions, the obtained superhydrophobic samples with large LS have good anti-friction and wear-resistant ability. The advantages of the facile preparation and excellent tribological properties will definitely expand the use of laser-machined superhydrophobic surfaces.

Experimental investigation on Stribeck curves of different elastic modulus materials under oil and water lubrication conditions

Purpose The purpose of this paper is to study the influence of friction coefficient of materials with different elastic modulus on the variation of velocity and load under water lubrication and oil lubrication conditions. Design/methodology/approach Low-viscosity lubricating oil and water were used as lubricants to test the friction performance of the ball-disc contact friction pair in the lubrication state on the universal micro-tribometer multi-functional friction and wear test system. Findings In the same speed range, the lubrication states from soft to rigid materials are not necessarily similar to each other. Generally, the material with low elastic modulus is suitable in low-viscosity lubricant environments, while the material with high elastic modulus has relatively smaller friction coefficients in oil-lubricated environments compared with water lubrication. However, the coefficients of polyethylene, polytetrafluoroethylen and polyoxymethylene are exceeded by rubber’s coefficients under water lubrication in the same experiment environments, and their lubrication states are not affected by lubricants. The friction coefficient of the friction pair decreases with the increase of loads; however, it does not apply to all materials. The friction coefficients of materials with smaller elastic modulus such as rubber under high loads are rather large. Therefore, the elastic modulus of the material under high loads is a factor to be considered. Originality/value The Stribeck curves study of the ball-disk contact friction pair comprising soft and rigid materials, whose elastic modulus is from hundreds of GPa to a few of MPa, was carried out. The influence of different speeds, loads and lubricants on the friction coefficient of the friction pair was revealed, which provided a research basis for the selection and matching of friction pair materials.

Effect of Particle Size on Tribological Properties of Rubber/Steel Seal Pairs Under Contaminated Water Lubrication Conditions

Abrasive wear is a common failure phenomenon that often limits the service life of seals. In this study, the abrasive wear test of acrylonitrile–butadiene rubber against steel was developed under conditions of lubrication contaminated with abrasives. The influence of particle size on coefficient of friction (COF) evolution, particle activities, wear morphologies, and damage mechanisms were discussed in detail. Results showed that the presence of abrasive particles dispersed in lubricated medium clearly deteriorates the tribological performance of the seal pairs. Two threshold values (approximately 7.5 and 75 μm) related to the “particle size effect” were obtained. And on this basis, the damage mechanism can be divided into three types. Several damage characteristics presented on respective worn surface, such as, cutting effect, rolling effect, the pinning effect of the “abrasive group,” an alternated feature with “ridge–valley–ridge,” or in the form of furrows and craters. In addition, the particles in the medium destroyed the lubricating film between the rubbing pairs and increased the COF and material removal capacity of tribo-pairs. Furthermore, the wear mode that clearly describes the wearing behavior of the seal pairs under abrasive-contained water lubrication conditions was identified. The results of this study enhanced our understanding of the wear degradation of rubber seal in all types of contaminated lubrication conditions.

Effect of reduced graphene oxide amount on the tribological properties of UHMWPE biocomposites under water-lubricated conditions

Ultra-high molecular weight polyethylene (UHMWPE) has been broadly utilized in hip and knee artificial implant due to its low friction coefficient, high wear resistance and good biocompatibility. However, some disadvantage properties such as low young’s modulus and low load bearing, anti-fatigue capacity limit application areas and wear debris of UHMWPE components cause implant failure. For this reason, reduced graphene oxide (RGO) filler was produced by green synthesis with vitamin C and the influences of RGO filler content on the tribological performance under distilled water lubrication condition were investigated and had been correlated with microstructure. RGO filled UHMWPE biocomposites were fabricated by firstly liquid phase ultrasonic mixing and then hot press molding. The characterization and experiment results revealed that the wear behavior of UHMWPE/RGO biocomposites were not only affected by the lubricant and binder properties of RGO, but also restricted by the content of RGO filler. The RGO filled UHMWPE biocomposites exhibited a lower wear rate and friction coefficient in comparison to the unfilled UHMWPE. The biocomposite with 0.7 wt% of RGO showed good interfacial bonding strength and excellent wear resistance. Furthermore, fatigue wear tracks reduced significantly on the same biocomposite surface. High crystallite size and microhardness value of UHMWPE/RGO-0.7 biocomposite was caused destroy the tribofilm formed on the Al2O3 counterface.

Role of SiC nanoparticles on tribological properties of atmospheric plasma sprayed 5 wt% SiC–Ni60 coatings

In order to comparatively investigate the role of SiC nanoparticles on tribological properties under dry and water-lubricated conditions, Ni60 and 5 wt% SiC–Ni60 coatings were deposited by atmospheric plasma technology. The morphologies and phase composition of coatings were inspected by scanning electron microscopy and X-ray diffraction, respectively. And friction interface of coatings was examined by X-ray photoelectron spectroscopy and high-resolution transmission electron microscope to reveal the wear mechanisms of coatings after friction. Results illustrated that SiC nanoparticles could function as reinforcing phases, inducing friction-reducing and anti-wear. And tribological properties of 5 wt% SiC–Ni60 coating under dry and water-lubricated conditions were superior to those of Ni60 coating. The analysis of worn surface revealed that SiC nanoparticles could fill pits on the surface of coatings. According to FIB-TEM analyses and XPS results, SiC nanoparticles released onto friction interface can undergo hydrolysis reaction under water-lubricated condition, and the film containing SiO2 is formed by the hydrolysis reaction of SiC nanoparticles, which improves good boundary lubrication effect.

Friction and Wear Properties of Oriented Fe<sub>2</sub>B with Different Cr Additions under Water-Lubricated Condition

In the present study, pure oriented Fe2B with Cr addition were prepared. The friction and wear properties of oriented Fe2B with different Cr additions were investigated by optical microscopy, scanning electron microscopy and 3D laser scanning microscope. Results indicate that fracture toughness of the cross section is higher than that of the longitudinal section invariably with the same Cr addition. Both cross and longitudinal sections, the fracture toughness value increases from 1Cr to 2Cr and decreases from 2Cr to 3Cr. Friction coefficient and wear loss of cross section are lower than those of the longitudinal section under the same Cr addition. For the identical grain orientation, the friction coefficient and wear loss rise from 1Cr to 2Cr and then drop from 2Cr to 3Cr. 2Cr-C sample has the lowest friction coefficient and wear loss. On the contrary, the friction coefficient and wear loss of 3Cr-L sample are the highest. Wear mechanisms of Fe2B alloy are brittle rupture and abrasive wear.

Tribological Properties of Polyether–Ether–Ketone-Based Coating under Mixed and Boundary Aviation Kerosene-Lubrication Condition

Because of its excellent tribological performance, polyether–ether–ketone (PEEK)-based coatings have been used extensively under mixed and boundary water-lubrication conditions. To verify that the PEEK-based coating is applicable to aviation kerosene, one advanced coating was proposed and two typical metals, namely, alloy steel 38CrMoAlA and tin bronze ZQPb17-4-4, were selected as counterparts. Four sets of experiments that involved a scuffing (step load) and Stribeck curve (step speed), constant load, and strengthened load were carried out, which showed that the counterpart material’s properties, such as its hardness, thermal conductivity, and composition, had an important effect on the tribological performance of the PEEK-based coating. Scuffing experiments showed that the PEEK-based coating against ZQPb17-4-4 exhibited better scuffing performance. Stribeck curve experiments showed that the PEEK-based coating against 38CrMoAlA was under the mixed lubrication condition over a wider range of speeds, and wear experiments (constant load and strengthened load) showed that the PEEK-based coating against 38CrMoAlA exhibited a relatively low coefficient of friction and low wear rate. The formation and appearance of the tribofilm on the surface of the counterparts influenced the wear mechanism of the PEEK-based coating. The PEEK-based coating showed excellent properties, especially when rubbed against 38CrMoAlA.

Enhanced tribological performance of alumina composites reinforced with acid-treated carbon nanotubes under water lubrication

Alumina composites reinforced with acid-treated multiwalled carbon nanotubes (MWCNTs) are prepared, and the tribological properties of the composite are investigated under water-lubricated conditions using a ball-on-disk technique against an alumina ball. The coefficient of friction (COF) in the steady-state region of the composite with acid-treated MWCNTs is found to be 0.06, which is 32–37% lower than that of the monolithic alumina and the composite with pristine MWCNTs. Microstructural observations and in-depth Raman spectroscopy analyses of the disk samples and counterparts before and after the friction tests reveal that the MWCNTs located in pits on the disk surface pull-out and that the resultant MWCNT fragments adhere to the friction surface of the counterparts. The enhanced tribological performance shown in the composite with acid-treated MWCNTs is mainly because the negatively charged functional groups adsorbed on the MWCNTs participate in the hydrogen-bond network of the hydrodynamic lubrication film and lead to acceleration of the transformation from a boundary lubrication regime to a mixed lubrication regime.

A hydrodynamic lubrication model and comparative analysis for coupled microgroove journal-thrust bearings lubricated with water

The novelty of this study is to develop a hydrodynamic lubrication numerical model for coupled microgroove journal-thrust bearings (or coupled bearings) under water-lubricated condition. In the present model, the continuity of the hydrodynamic pressure and the fluid field (or coupled hydrodynamic effect) at common boundary is considered to reveal the mutual effect between the hydrodynamic behavior of the journal bearing and the thrust bearing. The lubrication performances of the coupled microgroove bearing with three bottom shapes, i.e., isosceles triangle, right triangle, and left triangle, are studied comparatively. Additionally, the effects of the microgroove depth on the lubrication performances of the coupled bearing are discussed. The present study reveals that the coupled hydrodynamic effect generated by the coupled bearing can improve the lubrication performance for both the journal and the thrust bearing. The microgroove with left triangle bottom shape yields the optimal lubrication performance as compared to the other two. There is an optimal groove depth that generates the maximum load capacity and the minimum friction coefficient for both the journal and the thrust bearing.

Friction-Wear Characterization of Cathodic Arc Ion Plated CrC Coating under Different Lubrication Conditions

A CrC coating was deposited on YT14 cutting tools using a cathodic arc ion plating. The surface and cross-section morphologies, chemical elements and phases of obtained CrC coating were analyzed using a field emission scanning electron microscope, energy disperse spectrometer, and X-ray diffractometer. The tribological properties of CrC coating under the dry, water and oil lubrication conditions were investigated using a wear test, the effects of lubrication conditions on the friction coefficient and wear properties of CrC coatings were also discussed. The results show that, the average friction coefficient of CrC coating under the dry, water, and oil lubrication conditions are 0.76, 0.11, and 0.35, respectively, the wear mechanism is abrasive wear. The average residual stresses of worn tracks under the dry, water, and oil lubrication conditions are −231.1 ± 25.0, −210.4 ± 23.0, and −205.9 ± 2.0 MPa, respectively, of which the stress value under the oil lubrication condition is the smallest, showing its reduction wear property.

Study on the friction and wear performance of the micro-surface textured face seal under the water-lubricated conditions

Due to the poor lubricated performance of the low-viscosity lubricants (such as liquid oxygen and liquid hydrogen), the severe friction and wear of the seal’s pair for the high-speed turbopump in the cryogenic liquid rocket engine often occur, which may lead to the seal failure (excessive leakage or serious wear). For improving the tribological properties of the seal, the seal’s rotor with the micro-surface texture is proposed and the friction and wear performance of the seal pairs are studied. First, the theoretical model for solving the performance of the micro-surface textured face seal is developed. Second, the optimized structural parameters (dimple diameter, grooved area ratio and the dimple depth–diameter ratio) for the micro-surface texture are obtained, and the laser surface texturing method is applied to make the samples of the rotor. Third, the tribological properties of the micro-surface textured sealing ring are tested by the pin-disk tribology tester, and the comparisons between the friction coefficients and wear rate of the textured rotor ring and that of the ordinary steel disk and disk with the DLC coating are finished. The results show that optimized dimple diameter, grooved area ratio and the dimple depth–diameter ratio are 50 μm, 0.6 and 1, respectively, and the friction coefficients of the proposed rotor are 0.17 and 0.36, respectively, under the dry friction and water-lubricated conditions. The study is of great theoretical and experimental reference for designing the face seal under the low-temperature, low-viscosity and high-speed conditions in the cryogenic liquid rocket engine.

Comparative study of tribological properties of carbon fibers and aramid particles reinforced polyimide composites under dry and sea water lubricated conditions

Moving components used under air and lubricated conditions are constantly subjected to friction and wear, which poses a challenge to their reliability and service life. This work addressed the influence of short carbon fibers (SCF) and aramid particles (AP) on tribological performance of polyimide (PI) composites adding with polytetrafluoroethylene under dry and sea water lubrication conditions. A systematic study on the tribological mechanisms of SCF- and AP-reinforced PI composites was carried out. Under the controlled sliding conditions (i.e., velocity, pressure, and working conditions), the AP was more effective than SCF for enhancing the tribological performance under dry condition, but reversed under lubrication. Hard SCF exposed to the sliding interface could cause removal of the wear debris, thereby the tribofilm was patchy to lose excellent lubricated property. When sliding occurred under sea water lubrication, the weak interfacial interaction was beneficial to the formation of a robust boundary film for SCF-reinforced PI composite rather than AP-reinforced PI composite. Moreover, tribo-chemical reactions occurring between polytetrafluoroethylene and copper sustained the lubrication property of tribofilm and prevented tribo-corrosion when subjected to lubricated condition.

Effects of Typical Physical Properties on Tribological Behaviors of Three Kinds of Polymer Materials for Water-Lubricated Bearings

The stretching, shearing, deformation, peeling, and temperature rise phenomena at the micro–nano contact interface have a great influence on its tribological properties and significantly affect the service life of key moving parts made of polymers. The physical properties of the three typical polymer materials used for ship bearing polymer materials (ultra-high-molecular-weight polyethylene, synthetic rubber, and polypropylene) were examined to investigate their effects on the wear behaviors. The results showed that synthetic rubber has good wear resistance because of its excellent shear strength, tensile strength, and high initial thermoplastic deformation temperature. Low initial thermoplastic deformation temperature resulted in great wear to the polypropylene material under dry friction, whereas its good wettability resulted in good wear resistance under water-lubricated condition. The ultra-high-molecular-weight polyethylene had the poorest wear resistance under water-lubricated condition because it had the poorest shear strength and tensile strength. The knowledge gained herein provides a better understanding of the relationships between the physical behaviors of polymer materials and their friction and wear mechanisms, along with guidance for selecting and designing polymer friction pairs for ship bearings.

Preparation of Superhydrophobic 35CrMo Surface and Its Tribological Properties in Water Lubrication

The process of oil exploitation is often accompanied by the generation of the corrosive gases, metal particles and minerals, which results in very serious corrosion and wear of petroleum machinery and equipment, which can be greatly reduced by modification of the surface properties of the materials. According to the theory of molecular interaction, the friction effect of a rough surface is better than that of a smooth surface, while fabrication of surfaces with appropriate roughness may reduce the friction. We present the construction of a grooved texture on the surface of 35CrMo using a nano-pulse laser. We found that some micro-/nano-structures were created on the surface, and that a superhydrophobic surface with a water contact angle of 156° and a sliding angle of less than 10° was obtained. Groove textures of different depths produced by using various laser energy densities, the friction coefficient of the superhydrophobic samples was significantly reduced from 0.55 to 0.28 after laser surface texturing under water lubrication conditions. This shows the improvement of the tribological properties.

Tribological Performance of CF-PEEK Sliding against 17-4PH Stainless Steel with Various Cermet Coatings for Water Hydraulic Piston Pump Application

To improve the abrasion resistance performance of the critical tribopairs within water hydraulic piston pumps, tribological characteristics of the stainless steel 17-4PH and 17-4PH coated with Cr3C2-NiCr, WC-10Co-4Cr, Cr2O3 and Al2O3-13%TiO2 sliding against carbon fiber reinforced polyetheretherketone (CF-PEEK) composite under water-lubricated condition were experimentally studied using a pin-on-ring test bench with different working conditions. It has been demonstrated by the experimental results that the tribological behaviors of CF-PEEK/cermet coatings tribipairs were better than that of CF-PEEK/17-4PH tribopair under water lubrication. However, the Cr3C2-NiCr coating could be damaged under high rotational speed. Due to the reaction film produced by the Al2O3-13%TiO2 and water, the CF-PEEK/Al2O3-13%TiO2 material combination exhibits more excellent tribological behaviors than other tribopairs lubricated with water, and could preferentially be used in water hydraulic piston pumps.