Oil-lubricated Conditions Research Articles

Influence of SiC polytypes on the mixed lubrication regime of self-lubricating composites containing in situ generated 2D turbostratic graphite

Fe-based self-lubricating composites, in which SiC particles act as precursors to in situ generated 2D turbostratic graphite as a lubricating phase, were produced via powder injection moulding (PIM). In order to study the precursor influence on the solid lubricant structure and properties, hexagonal (α) and cubic (β) SiC polytypes were used. The composites were tribologically tested in dry and low-viscosity oil-lubricated conditions. Distinct precursors did not lead to significant differences between composites. However, due to the highly disordered graphite-rich tribolayer formation, they do provide lubricity, low friction coefficient, and high wear resistance, even in oil-lubricated conditions.

The Tribological and Mechanical Properties of PI/PAI/EP Polymer Coating under Oil Lubrication, Seawater Corrosion and Dry Sliding Wear

To investigate the tribological performance of a copper alloy engine bearing under oil lubrication, seawater corrosion and dry sliding wear, three different PI/PAI/EP coatings consisting of 1.5 wt% Ce2O3, 2 wt% Ce2O3, 2.5 wt% Ce2O3 were designed, respectively. These designed coatings were prepared on the surface of CuPb22Sn2.5 copper alloy using a liquid spraying process. The tribological properties of these coatings under different working conditions were tested. The results show that the hardness of the coating decreases gradually with the addition of Ce2O3, and the agglomeration of Ce2O3 is the main reason for the decrease of hardness. The wear amount of the coating increases first and then decreases with the increase of Ce2O3 content under dry sliding wear. The wear mechanism is abrasive wear under the condition of seawater. The wear resistance of the coating decreases with the increase of Ce2O3 content. The wear resistance of the coating with 1.5 wt% Ce2O3 is the best under-seawater corrosion. Although Ce2O3 has corrosion resistance, the coating of 2.5 wt% Ce2O3 has the worst wear resistance under seawater conditions due to severe wear caused by agglomeration. Under oil lubrication conditions, the frictional coefficient of the coating is stable. The lubricating oil film has a good lubrication and protection effect.

Effect of laser texturing bulges on tribological properties of 316L stainless steel

The laser surface texture process will inevitably produce the edge of material surface texture bulges. Currently, laser processing bulges are generally polished directly, but this method ignores its impact on the friction pairs. In this paper, the tribological properties of polished and unpolished textured surfaces were investigated under dry friction, oil lubrication, and seawater lubrication conditions using three shapes of texture (grooves, square pits, and round pits) prepared on the surface of 316L stainless steel. The results show that the polished surface of 316L stainless steel texture increases wears, and the friction mechanism is mainly adhesive wear, while the unpolished surface of the texture has less wear, and the friction mechanism is mainly abrasive wear. The method and principle of using machining bulges to improve the wear resistance of friction pairs are discussed to address the differences in the tribological performance of entire friction pairs due to the influence of machining bulges of different shapes of texture.

Friction and wear of multiple steel wires in a wire rope

The fretting wear among the steel wires aggravates the wire rope’s fatigue damage, affects the service performance of the wire ropes, and threatens mine hoisting safety. In this paper, the practical friction behavior and wear mechanism among the wires in the wire rope are investigated. A series of tests were carried out on multiple steel wires in helical contact and tension-torsion coupling under different fretting parameters, twisting parameters, and lubrication conditions by self-made friction and wear testing machine. The results show that the coefficient of friction (COF) among the steel wires decreases slightly with increasing lateral loads and tension, and the effect of twist angle on the COF has opposite results under different lubrication conditions. Lateral loads, tension of the steel wires, twist angle, and lubrication condition all affect the fretting morphology among the steel wires. Fretting wear with larger twist angle structure leads to more energy loss. The energy loss of fretting is directly related to the fretting morphology among the contact surfaces, and the dissipated energy is lower in the two forms of complete slip and sticking. The wear depth and width increase with the increase of lateral loads, steel wire tension, and twist angle. And the wear width and depth under dry friction conditions are higher than those under oil lubrication conditions. In addition, the wear mechanism under dry friction conditions is mainly abrasive wear, adhesive wear, and fatigue wear. And the wear mechanism under oil lubrication conditions is mainly abrasive wear and fatigue wear.

Tribofilm formation mechanism and friction behavior of polycrystalline diamond compact after cobalt leaching added molybdenum disulfide nanoparticles in different base oils

To investigate the friction and wear properties of polycrystalline diamond compact after cobalt leaching(PDCACL)and the formation mechanism of lubricating oil film under different base oil lubrication conditions, AFM, SEM, EDS and XPS were used to analysis and discuss the friction behavior, microstructure and friction film formation process of PDCACL after adding nano molybdenum disulfide in different base oils. The results showed that there are differences in the speed and thickness of the friction protective film formed by PDCACL under different kinds of base oil lubrication environment. The physical and chemical properties of base oil are the key factors affecting the wear mechanism of PDCACL and the formation of friction film.

Fingerprint-inspired surface texture for the enhanced tip pinch performance of a soft robotic hand in lubricated conditions

The core capabilities of soft grippers/soft robotic hands are grasping and manipulation. At present, most related research often improves the grasping and manipulation performance by structural design. When soft grippers rely on compressive force and friction to achieve grasping, the influence of the surface microstructure is also significant. Three types of fingerprint-inspired textures with relatively regular patterns were prepared on a silicone rubber surface via mold casting by imitating the three basic shapes of fingerprint patterns (i.e., whorls, loops, and arches). Tribological experiments and tip pinch tests were performed using fingerprint-like silicone rubber films rubbing against glass in dry and lubricated conditions to examine their performance. In addition to the textured surface, a smooth silicone rubber surface was used as a control. The results indicated that the coefficient of friction (COF) of the smooth surface was much higher than that of films with fingerprint-like textures in dry and water-lubricated conditions. The surface with fingerprint-inspired textures achieved a higher COF in oil-lubricated conditions. Adding the fingerprint-like films to the soft robotic fingers improved the tip pinch gripping performance of the soft robotic hand in lubricated conditions. This study demonstrated that the surface texture design provided an effective method for regulating the grasping capability of humanoid robotic hands.

Performance of elastomeric spur gear under dry and oil-lubricated conditions

The fatigue and tribological performance of thermoplastic-based gears have been investigated extensively so far, but no such work has been done on elastomeric gears. In the current work, the feasibility of utilizing elastomeric material for gear applications was investigated. Initially, the sliding contact performance of an elastomeric material under dry and oil-lubricated conditions was examined. Subsequently, the elastomeric gears were subjected to bending and contact loads under dry and oil-lubricated conditions. The elastomeric gear exhibited only tooth root cracks owing to bending fatigue under both dry and oil-lubricated conditions. Unlike thermoplastic-based gears, elastomeric gears do not exhibit thermal deformation or wear failures. The presence of voids in the elastomeric material caused multiple microcracks under dry conditions. Oil-lubricated elastomeric gear controlled crack growth at the tooth root and changed the cracking mode from tensile to shear under the high load condition.

Lubrication performance of kite-shaped microtexture under hydrodynamic lubrication

New kite-shaped textures are designed in this paper to improve the lubrication performance of tribological systems under hydrodynamic lubrication. Moreover, pressure distribution and load-carrying capacity of the kite-shaped textures under fixed working conditions are solved using Reynolds' equation based on the form of mass conservation. Lastly, the influence of kite-shaped textures on the friction coefficient under different geometric parameters is investigated. Moreover, a double-layer composite kite-shaped texture is designed, and the influence of parameters on lubrication performance is investigated. Numerical simulations and experiments are used to find the optimal parameters and effectively reduce the friction coefficient, thus providing a reference for reducing frictional wear in mechanical systems under full-film oil lubrication conditions.

Surface texture and heat treatment on the friction performance of cam tappet experimental and fluid-solid coupling numerical study

In order to improve tribological properties of tappets made of GCr15 bearing steel, a combination of martensitic heat treatment and surface texture was applied to the GCr15 bearing steel. The texture was designed based on a fluid-solid coupling simulation performed using COMSOl, and effectiveness of the designed texture was verified by performed wear tests using a pin-disk line contact rotary motion tester under oil lubrication condition. The worn surface morphology and wear mechanism for the friction pair were analyzed with three-dimensional scanning microscopy and scanning electron microscopy to reveal the antifriction behavior and wear resistance. Results of the study show that the heat treatment increased the surface hardness and significantly reduced wear of the GCr15 bearing steel. The designed surface texture helped reduce the contact area, store tiny wear debris, and increase the oil film pressure, thus improving the tribological performance. However, the texture edge was prone to severe plastic deformation due to the stress concentration and lowered lattice confinement. The martensitic heat treatment involving tempering effectively reduced plastic flow at the edge of texture. The combination of texture and the martensitic heat treatment considerably improved the tribological properties of GCr15 steel.

Sliding contact performance of injection moulded and selective laser sintered polyamide under dry and lubricated conditions

PurposeThis paper aims to understand the effect of the manufacturing process on the frictional and wear performance of polyamide.Design/methodology/approachPin specimens were manufactured through injection moulding (IM) and selective laser sintering (SLS) manufacturing processes. The friction and wear performance was evaluated using a pin-on-disc configuration under dry and oil-lubricated conditions. The friction coefficient, wear resistance and surface temperature of specimens were measured, and failure morphology analysis was carried out to understand the mechanism.FindingsSLS material exhibited significantly less friction, wear and surface temperature than IM material under dry conditions. Reduced ductility due to the sintering contributes to reduced friction, wear and heat generation. Under the dry condition, IM material exhibited plastic flow and roll-shaped deformation, whereas SLS material exhibited only local degradation due to its lesser ductility. Lubrication reduced friction and temperature for both SLS and IM materials. The porous nature of the sintered surface absorbed the lubricant and released it while sliding, which is confirmed by the brown-coloured wear track.Originality/valueThe study provides valuable input to the designers on the sliding contact performance of commonly adopted two different manufacturing processes of polymers; IM and SLS manufacturing.

Friction dependence on the textured structure of an amorphous carbon surface: A reactive molecular dynamics study

Amorphous carbon (a-C) film provides ultralow friction when combined with lubricating oil. However, it is unclear how textured surfaces affect the friction behavior of a-C at atomic scale, specifically the transformation of interfacial structure and the flow of lubricating oil, owing to the limitations of experimental characterization. Here, a-C films with different textured surfaces were fabricated, and the friction behaviors of mating a-C surfaces with textured parameters, including nanoscale depth and width, were examined by reactive molecular dynamics simulation. Results indicate that compared to that under dry condition, the introduction of a textured surface reduces the friction coefficient of a-C under oil lubrication condition. However, its efficiency highly depends on the depth and width of textured surface, exhibiting different effects on hydrodynamic lubrication. The increase in textured depth causes the friction coefficient decreased first and then increased, attributing to the lubrication from hydrodynamic to boundary state as primary mechanism. The regional aggregation of lubricant atoms with a textured width on the a-C surface occurs at the friction interface following the increased friction coefficient. These results provide insights into the underlying friction mechanism of a-C films induced by surface texturing and enable the development of highly efficient lubrication systems for applications.

Understanding the influence of graphene-based lubricant/coating during fretting wear of zircaloy

In order to study the relative effectiveness of oil-based and graphene-based lubrications towards suppressing the friction and wear damage of zircaloy-4 during low amplitude linear reciprocatory wear, fretting wear tests were performed with varying normal loads (5–20 N) under unlubricated, oil-lubricated (using Castrol TDN-81) and graphene-lubricated/coated (using ∼7 layers graphene film) conditions against stainless steel ball. While the oil-based lubricant has been found to be more effective towards lowering the co-efficient of friction at lower loads, the effectiveness of the graphene-based lubricant/coating increase significantly with an increase in load. In the contexts of suppressing the extent/severity of wear damage, the graphene-based lubricant/coating has been found to be significantly more effective than the oil-based lubricant. In fact, increase in effectiveness of the graphene-based lubricant/coating with load results in the wear volume remaining nearly invariant upon increase in load; thus, causing reduction in wear rate. This is in contrast to the increase in wear volume/rate with increase in load for the unlubricated and oil lubricated conditions; such that the wear volume and rate are lower for the graphene-lubricated/coated condition by more than a factor of 2 with respect to the oil-lubricated condition at 20 N. In the unlubricated condition severe sub-surface cracking induced material removal/delamination, presumably aided by incorporation of Fe and O due to tribochemical reaction, form the major mechanisms of wear damage of zircaloy-4. By contrast, all these get suppressed in the presence of the graphene-based lubricant/coating, even at 20 N; thus, leading to significant reduction in the overall wear damage.

Tribological Behavior of Titanium-Sintered Composites with Ring-Shaped TiN Dispersoids

The wide applicability of titanium (Ti) has prompted the analysis to improve its mechanical strength through the addition of different alloying elements. Among these, Ti materials with pre-mixed pure Ti and titanium nitride (TiN) powders as the starting materials have exhibited improved mechanical properties and tribological performance. In this study, the tribological properties of Ti matrix composites with ring-shaped TiN dispersoids were evaluated. The materials were fabricated from pre-mixed pure Ti powder and core–shell structured Ti–(N) powder, which were prepared by heat treatment at 1273 K under N2 gas. The tribological behavior of the Ti–TiN composites was studied by varying the applied load using a ball-on-disk wear test under oil lubrication conditions. The initial familiarity period of the Ti–TiN composites decreased. Subsequently, compared to the pure Ti specimen employed as a reference material, the friction coefficient was significantly lower and more stable. This is attributed to the ring-shaped, hard TiN dispersoids, which prevented the adhesion phenomenon and improved the oil film formability owing to the increase in microhardness and abrasive wear resistance of the nitrogen solid solution in the core region.

Frictional and material deformation of aluminium alloy in cold forging test under different derivatives of palm oil lubrication condition

Frictional and material deformation of aluminium alloy in cold forging test under different derivatives of palm oil lubrication condition

Experimental Investigation of Triboelectrification Behaviour in the Friction Process

The triboelectrification phenomenon can occur during the friction process of metal contact pairs. An in-depth understanding of triboelectrification behaviour is incredibly beneficial to controlling friction and wear. However, due to the complexity of the driving mechanism, it is still challenging to gain a thorough understanding of the triboelectrification behaviour of metal–metal contact pairs. To further reveal the triboelectrification behaviour during the friction process of metal pairs, wear experiments of GCr15 steel–cast iron were carried out on a CFT-I tribometer under oil-free and oil lubrication conditions. The triboelectric current signal was collected during the investigation, and its variation was discussed. The result shows that the varying trend of the triboelectric current was consistent with that of the friction coefficient in the friction process. The triboelectrification of similar metal contact pairs primarily driven by material transfer was closely related to friction and wear conditions.

High-pressure wear behavior of laser clad MoNiTaTiV high-entropy alloy coating sliding against QBe2.0 beryllium bronze under dry and oil-lubricated conditions

Sealing engineering equipment, especially in a harsh environment (e.g. high-pressure), is frequently subjected to tribological impacts during service, leading to an accelerated failure of the seal parts. In this study, an effective strategy was proposed to reduce the wear of the seal part, utilizing high entropy alloy (HEA) coating. A novel wear-resistant MoNiTaTiV HEA coating was designed and prepared on the substrate of GCr15 steel via laser cladding. The microstructure, chemical composition and microhardness of the HEA coating were examed by scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive spectrometer (EDS) and nanoindentation. The wear property of the HEA coating sliding against its QBe2.0 counterpart under dry and oil-lubricated conditions at high-pressure was investigated deeply. As a result, the HEA coating exhibits BCC and TiN ceramic phases and its hardness reaches approximately 1099.7 HV, which is 3.7 times higher than that of the substrate. Additionally, the HEA coating shows superior wear properties to substrate under dry and oil-lubricated conditions, which is closely related to the high hardness of HEA coating reinforced by TiN particles. The adhesion layer and oxide layer were formed on the HEA coating, transferring the two-body to three-body wear. The QBe2.0 counterpart and MoNiTaTiV coating could be a promising anti-wear tribo-pair for seal parts under dry and oil-lubricated conditions.

Performance of selective laser sintered polyamide spur gear under dry and lubricated conditions

The durability of a selective laser sintered (SLS) polyamide gear was evaluated using an in-house gear test rig under dry and oil-lubricated conditions. The lubricated SLS gear exhibited inferior contact fatigue performance at lower torques than that under dry conditions. Cyclic contact stress coupled with sliding motion diffuses the lubricating oil into the porous subsurface and reduces the contact fatigue strength of the gear tooth. The failure of the SLS gear under dry conditions exhibited the polishing effect, thermal softening with surface cracks, and thermal bending at 1.8, 2.5, and 3.5 Nm, respectively, whereas failure of the SLS gear under the oil-lubricated condition was only pitting for all the considered conditions. The lubricated gear exhibited superior performance at a higher torque than the gears in the dry-running condition, owing to its improved thermal stability.

Synergistic lubrication mechanisms of molybdenum disulfide film under graphene-oil lubricated conditions

Single solid or liquid lubricant cannot meet the ever-increasing lubricating performance of mechanical motion under extreme operating conditions. Solid-liquid synergistic lubrication could effectively solve the friction and wear problems due to the cooperation of solid and liquid lubricant. Herein, the solid–liquid composite coating was prepared via molybdenum disulfide (MoS2) film under graphene hybrid gear oil lubrication conditions. Its anti-friction and anti-wear abilities were reduced by 13.0% and 37.4% compared with gear oil lubricated MoS2 film, and 46.7% and 97.1% lower than those of only MoS2 film, respectively. More importantly, the graphene-like transfer film at frictional contact interfaces was formed. Hence, the excellent lubrication function of MoS2-based solid–liquid lubricating coating was attributed to not only the structural advantages of MoS2 and graphene, but also the solid–liquid synergism and transfer film, thereby enhancing the interfacial load-bearing capacity and anti-friction/wear behaviors.

Wear Resistance Mechanism of Sub-Nano Cu3P Phase Enhanced the Cu-Pb-Sn Alloy

High Cu-Pb-Sn, as the material for bimetallic cylinder block, is widely used in the selection of wear-resistant parts due to its excellent wear reduction, thermal conductivity, fatigue resistance, and strong bearing capacity, such as bearings and bearing bushes, aerospace pump rotor, turbine and guide plate, etc. However, because its wear resistance is not enough to meet the harsh conditions of high temperature, high speed, and heavy load, the research on high wear resistance Cu-Pb-Sn materials has important theoretical significance and application value for the application of bimetallic materials. ZCuPb20Sn5 alloy was taken as the research object to analyze the influence mechanism of its different microstructure and mechanical properties on the friction and wear properties of alloy materials. Friction experiments under two conditions of oil lubrication and dry friction were carried out on the MMW-1A pin-on-disc friction and wear testing machine. The wear resistance and wear mechanism of ZCuPb20Sn5alloy under the action of Cu3P were discussed, and a high wear-resistant Cu-Pb-Sn alloy for bimetal cylinder block was prepared. The results show that with the increase of P content, both the friction coefficient and wear rate decrease, and the wear reduction of ZCuPb20Sn5 alloy increases. Under oil lubrication conditions, the friction coefficient decreases by 21.4% and the wear rate decreases by 85.5% compared with that without adding P. The friction-reducing and wear-resistant properties of ZCuPb20Sn5 alloy materials are increased. In dry friction and oil lubrication, the mass wear amount of ZCuPb20Sn5 alloy material decreases with the increase of P element addition, and the change rule of alloy wear amount is consistent under the two methods. In the process of friction and wear, adhesive wear occurs, and the wear amount of the alloy material increases. With the increase of P content, the lead particles are refined and evenly distributed, which promotes the formation of a uniform self-lubricating lead film during the friction process and reduces the degree of adhesive wear. The appearance of Cu3P reduces the contact area of the friction surface and weakens the adhesive wear, so the wear rate is reduced.

Effects of surface texturing and laminar plasma jet surface hardening on the tribological behaviors of GCr15 bearing steel

Surface texturing (ST) and laminar plasma jet (LPJ) surface hardening were applied to GCr15 bearing steel to improve its wear resistance. Ball-on-disk reciprocating tests were then conducted under dry and oil-lubricated conditions to investigate the tribological behaviors. Morphology and evolution of the frictional interfaces were analyzed by SEM images to reveal the anti-wear mechanism. Results show that LPJ surface hardening can remarkably reduce the wear of GCr15 bearing steel by increasing surface hardness and thus decreasing the actual contact. Whether ST can improve the wear of GCr15 bearing steel mainly depends on the evolutions of frictional interface and wear mechanisms, namely the competitive relationship of stress concentration with trap effect or hydrodynamic pressure effect under dry friction or oil-lubricated condition.