Lubricant Transfer Research Articles

Graphene-reinforced amorphous carbon film for heat-assisted magnetic recording head: A molecular dynamics and density functional theory study

Heat-assisted magnetic recording (HAMR) is technology which can extend the area density to 10 Tb/in2. The high temperature at the head/disk interface (HDI) leads to lubricant degradation and transfer to the HAMR head. The friction characteristics and reliability of HAMR HDI are reduced. The graphene-reinforced amorphous carbon (a-C) film may be a potential coating for HAMR head. The molecular dynamics and density functional theory are used to investigate the adsorption and diffusion behaviors of lubricants on the graphene-reinforced a-C film. The thermal stability of graphene-reinforced a-C film is studied. As the temperature increases, D-4OH lubricants exhibit uniform sliding on the surface of graphene-reinforced a-C film. And the covalent bonds between the graphene and the a-C film are broken. The graphene-reinforced a-C film effectively prevents the decomposition of the lubricants. The graphene makes the surface of the a-C film electrically neutral, which improves the inertness and reduces the adsorption capacity of the D-4OH lubricant end groups. Compared to uncovered a-C film, the graphene-reinforced a-C film has better thermal stability. The graphene-reinforced a-C film with high thermal stability can minimize the adsorption and degradation of lubricants on the HAMR head, and improve the reliability of HAMR HDI.

Macroscopic liquid superlubric triboelectric nanogenerator: An in-depth understanding of solid-liquid interfacial charge behavior

Triboelectric nanogenerator (TENG) has been seen as one of the most promising energy harvesting technologies. However, there are an irreconcilable contradiction between low friction and high electrical output performance of the TENG. Here, we have devised a macroscale liquid superlubric triboelectric nanogenerator based on solid-liquid-solid structure, leveraging the concept of liquid superlubricity technology, resulting in a remarkable increase in both the open circuit voltage and short-circuit current by 53.0 % and 58.4 %, respectively. This huge increase in electrical output performance is accompanied by a 99.1 % reduction in friction coefficient (≈ 0.0025) and 99.993 % reduction in wear rate (≈ 0.76×10−7 mm3/N·m), when compared to those of a lubricant-free triboelectric nanogenerator. This work delves into the lubrication and charge transfer mechanisms. The liquid superlubricity technology achieves friction reduction through a hybrid mechanism combining boundary and hydrodynamic lubrication. And the high outputs arise from the charges transfer at solid-liquid interface. The triboelectric charges generated by the friction pair are transferred from solid to the lubricating liquid. Meanwhile, the lubricating liquid promotes electron transfer and contributes additional electrons. Our work provides profound insights into the lubrication and charge transfer mechanisms at solid-liquid interfaces, and addresses the paradox of high output and low friction in TENGs.

Mist-control of polyalphaolefin (PAO) lubricants using long pairwise end-associative polymers

Accidental release of pressurized hydrocarbon fuels and lubricants are a major fire hazard due to the formation of small droplet mists that can readily evaporate and ignite. Mist control through increasing droplet size and suppressing droplets has been previously demonstrated with high molecular weight polymer additives, but traditional long polymer additives do not survive the pumping that would usually precede accidental release. This constraint inspired associative polymer additives that can transiently form the high molecular weights needed for mist control, while reversibly breaking during pumping. A prior study demonstrated the efficacy of such a system in fuel: long telechelic polycyclooctadiene (PCOD) with pairwise associating acid and base end-groups. Here, we address an obstacle to applying this same polymeric system in a polyalphaolefin (PAO) solvent—its poorer solvent quality for PCOD than fuel. We measured the effects of the end-associative PCOD compared to a non-associative control on the rheological properties of solutions in both PAO (a common lubricant and heat transfer fluid) and decahydronapthalene (decalin, a solvent with PCOD solubility similar to fuel) in shear and extension, and connect those rheological modifications to observed changes in PAO spray under simulated accidental release conditions. The PCOD additives demonstrated substantial mist control in PAO, both in terms of reduced spray angle and droplet suppression. Despite the worse solubility in PAO and thus smaller effective coil size, these associative PCOD additives are effective at the low concentrations (¡0.1 wt %) necessary for practical use as a safety measure.

Micro Lubrication and Heat Transfer in Wedge-Shaped Channel Slider with Convex Surface Texture Based on Lattice Boltzmann Method

Hydrodynamic lubrication is widely used between two relatively moving objects, and the effect of fluid flow state and temperature distribution on lubrication performance in wedge-shaped gaps is a popular topic to study. In this paper, the incompressible double-distribution lattice Boltzmann method (LBM) is applied to study the effect of micro convex surface texture on micro lubrication and heat transfer in wedge-shaped channels. By comparing this model with the analytical solution of an infinitely wide wedge slider, the maximum pressure calculated by LBM is 0.1081 MPa, and the maximum pressure calculated by the Reynolds equation is 0.1079 MPa. The error of the maximum pressure is 1.11%, and the Reynolds equation result is slightly smaller. The reason is that the Reynolds equation ignores the influence of fluid inertia force on oil film pressure. The results indicate that the application of LBM can be used to study lubrication problems. Compared with the Reynolds equation, LBM can calculate the velocity field and pressure field in the film thickness direction, and can also observe precise flow field details such as vortices. Three micro convex texture shapes were established to study the effects of different convex textures on micro lubrication and oil film temperature distribution, and the velocity distribution, temperature distribution and oil film pressure along the oil film thickness direction were given. Under the same conditions, comparing the oil film pressure with and without surface texture, the results show that the maximum oil film pressure with surface texture 3 is increased by about 4.34% compared with that without surface texture. The slightly convex texture can increase the hydrodynamic lubrication effect and obtain greater load-bearing capacity, helping to reduce the possibility of contact friction. The results show that the convex surface texture can improve the hydrodynamic lubrication performance, increase the load carrying capacity and reduce the possibility of contact friction, and the convex surface texture can influence the temperature distribution of the oil film. At 3.6 mm in the slider length direction and 7.5 μm in the oil film thickness direction, the temperature of surface texture 1 is 402.64 K, the temperature of surface texture 2 is 403.31 K, and the temperature of surface texture 3 is 403.99 K. The presence of vortices is captured at a high convergence ratio.

Self-lubricating and wear-resistant epoxy resin coatings based on the “soft-hard” synergistic mechanism for rapid self-healing under photo-thermal conditions

Mechanical components made of alloy steel are susceptible to severe surface wear after long periods of operation. The construction of protective coatings with high wear resistance and self-healing properties provides references for solving this problem. Herein, a highly wear-resistant coating (named as C-EP/PFW) that can rapidly self-healing under photothermal conditions was constructed by introducing both a novel phase-change material (polytetrafluoro-wax) and polydopamine-functionalized carbon nanotubes (PDA/CNTs) into the epoxy resin. The melt-phase transition of PFW at approx. 120 °C induces intermolecular phase migration and repair of the damaged area. The PDA/CNTs can act as microscopic bearings to enhance the load-bearing capacity of the composite coating, they can also construct thermal conductivity networks to enhance the thermal conductivity and repair efficiency of the coating. Based on the perfect combination of CNTs' excellent thermal conductivity and PDA's photothermal conversion capability, the average repair rate of the composite coating was increased by 20.7 % than pure EP/PFW coating. Additionally, the C-EP/PFW coatings in both dry and wet friction environments (seawater and sunflower oil) exhibited excellent self-lubricating properties. This is attributed to the synergistic of the soft lubricating phase on the repair of the lubrication transfer film and the microscopic slipping layer constructed by the CNTs at the tribofilm. The C-EP/PFW coatings, which are capable of rapid self-healing in thermal environments, provide a reference for the construction of highly wear-resistant protective layers on the surfaces of steel mechanical components.

The Effect of Slider Configuration on Lubricant Depletion at the Slider/Disk Contact Interface

With decreasing clearance between the protrusion of a slider and a disk interface, there is a higher likelihood of contact occurring during shock or vibration experienced by hard disk drives (HDDs), which may induce lubricant depletion. Based on the molecular dynamics (MD) model of perfluoropolyether lubricant with a coarse-grained beads spring approach, we compared the slider configurations’ influence on the lubricant transfer volume quantitatively. By further investigating the parameters of the cylindrical asperities, including the width and depth, as well as considering the asperity amounts of the slider, we successfully observed the lubricant depletion process during slider and disk contact. The results demonstrate that the penetration depth was reduced as the asperity amount increased, mainly owing to the increased contact area between the surfaces. The decreasing depth of the asperity and the increasing width of the asperity helped to reduce the depletion volume. In addition, the utilization of a cylindrical slider configuration can contribute to a reduction in lubricant depletion resulting from contact between the head and disk.

Enhancement of the mechanical and tribological properties of self-lubricant Mo2N–Ag composite film by adding amorphous SiNx

In this paper, the Si was introduced into the Mo2N–Ag matrix to synthesize the Mo2N–Ag-SiNx composite films using the magnetron co-puttering technology, designed to provide low-friction and long-term green tribological solutions for the demanding applications used at elevated temperatures. The results showed that the fcc-Mo2N, fcc-Ag, and amorphous SiNx were the main phases in the composite films. Adding Si of above 1.3 at.% could increase the hardness as well as the elastic modulus to ∼21 and ∼245 GPa. The average friction coefficient (COF) at room temperature (RT) exhibited a slight effect from the Si content, and its value was kept at 0.54–0.60, regardless of Si content. However the RT wear rate was significantly enhanced by adding Si of 1.3 at.%, due to the enhancement on the mechanical properties. At 600 °C, the COF decreased from 0.24 at 0 at.% Si to 0.19 at 5.0 at.%, but further increasing the Si content led to an increase in COF. The wear resistance was significantly enhanced by adding Si. It was mainly influenced by the lubricant transfer layers.

Impact of induced magnetic field on ferromagnetic ternary and hybrid nanofluid flows with surface catalyzed reaction and entropy generation assessment

Ternary and hybrid nanofluid flows have a wide range and diverse applications including lubrication, biomedical applications, energy conservation, and heat transfer, and continuous research in this subject is expected to discover new and inventive applications in the future. Aiming the same, the current research is intended to observe the responses of ferromagnetic nanoparticles in a dissipative comparative evaluation of ternary and hybrid nanoliquid flows along an exponentially extended surface under the consequences of an externally induced magnetic field in a porous media. Three distinct forms of ferroparticles—cobalt ferrite (CoFe2O4 ), magnetite (Fe3O4 ), and manganese zinc ferrite (Mn-ZnFe2O4 )—are taken into account using ethylene glycol as the fundamental fluid. The ternary nanofluid is comprised of (CoFe2O4+MnZnFe2O4+Fe3O4 /Ethylene glycol) combination. Whereas (CoFe2O4+MnZnFe2O4 /Ethylene glycol) mixture forms a hybrid nanofluid. A surface-catalyzed reaction is also introduced to regulate the homogeneous and heterogeneous (H-H) reactions and to commence the reaction in a comparatively shorter time. The entropy generation assessment is performed for ferromagnetic ternary and hybrid nanofluid flows. The envisioned mathematical model is transformed into a dimensionless system using a valid non-similarity transformation. The engagement of the non-similar solution eradicates the chance of parameters involving variable terms. The numerical solution for the various distributions is obtained by implementing the bvp4c technique with distinct parameters. Graphical demonstrations and tabular outcomes are given to illustrate the role of emergent parameters. Findings revealed that for surface-catalyzed parameter the concentration profile dwindled more for hybrid nanofluid. Furthermore, hybrid nanofluid flow produces less entropy than ternary nanofluid flow. In addition, it is witnessed that the induced magnetic field is stronger in the case of ternary nanofluid than hybrid nanofluid for increasing magnetic Prandtl number. The corroboration of the presented model is also given.

A new method to establish coupled multi-physics model of lubricated pin-hole oscillating pair

Under severe working conditions, about 10 % of the total engine friction loss originates from the piston pin-hole oscillating pair, significantly impacting the engine's reliability. Nevertheless, a systematic analysis encompassing the multi-physics environment (including lubrication, dynamics, and heat transfer) and their coupled behaviors is still lacking. A new coupled modeling method is proposed to achieve this, which can account for thermal deformation and frictional heat generation. All key components in this study are represented as three-dimensional flexible bodies, enabling a thorough characterization of the intricate secondary motions influencing lubrication. The method is applied to a lubricated oscillating pair test system, and a 1:1 simulation model is established. Experimental results also affirm its high accuracy. The model calculation results demonstrate that thermal deformation constrains pin secondary motions and increases axial load inhomogeneity. After factoring in fluid and asperity friction heat, the average friction coefficients at the small end hole (SEH) and pin base hole (PBH) increase by 1.8 % and 11.3 %, respectively. Furthermore, a parametric analysis is conducted, and the instantaneous friction coefficient curves under different loads/temperatures/frequencies are given. These findings can offer valuable insights into the tribological design of oscillating pairs.

Nanofluids Minimal Quantity Lubrication Machining: From Mechanisms to Application

Minimizing the negative effects of the manufacturing process on the environment, employees, and costs while maintaining machining accuracy has long been a pursuit of the manufacturing industry. Currently, the nanofluid minimum quantity lubrication (NMQL) used in cutting and grinding has been studied as a useful technique for enhancing machinability and empowering sustainability. Previous reviews have concluded the beneficial effects of NMQL on the machining process and the factors affecting them, including nanofluid volume fraction and nanoparticle species. Nevertheless, the summary of the machining mechanism and performance evaluation of NMQL in processing different materials is deficient, which limits preparation of process specifications and popularity in factories. To fill this gap, this paper concentrates on the comprehensive assessment of processability based on tribological, thermal, and machined surface quality aspects for nanofluids. The present work attempts to reveal the mechanism of nanofluids in processing different materials from the viewpoint of nanofluids’ physicochemical properties and atomization performance. Firstly, the present study contrasts the distinctions in structure and functional mechanisms between different types of base fluids and nanoparticle molecules, providing a comprehensive and quantitative comparative assessment for the preparation of nanofluids. Secondly, this paper reviews the factors and theoretical models that affect the stability and various thermophysical properties of nanofluids, revealing that nanoparticles endow nanofluids with unique lubrication and heat transfer mechanisms. Finally, the mapping relationship between the parameters of nanofluids and material cutting performance has been analyzed, providing theoretical guidance and technical support for the industrial application and scientific research of nanofluids.

LMJSSP for analysis of prophylactic lubricants, spermicides and residues

DNA evidence in sexual assault cases have proven increasingly difficult to obtain and analyse due to increased condom use. With more interest in alternatives to DNA evidence, prophylactic lubricants, spermicides and residues may be interesting prospects. Current interest in the analysis of prophylactic residues focuses on the evaluation and identification of lubricants and constituents, primarily through gas chromatography or Fourier transform infrared spectroscopy. Though cost-effective methods, extensive sample preparation and destructive modes of analysis remain an area for improvement. As a result, the focus has since shifted to ambient ionization methods that offer adequate sensitivity and reduced sample preparation. The Liquid Microjunction Surface Sampling Probe (LMJSSP) is a versatile ambient ionization source that employs a probe that supports a continuously flushing droplet that extracts analytes when placed in contact with a surface. The analytes are aspirated into the mass spectrometer with a Venturi pressure. In this work we use the LMJSSP to analyse the trace transfer of condom lubricant to different types of fabric (cotton, cotton-spandex, and denim). Furthermore, we examine the sensitivity and storage conditions for the direct analysis method on different swab types (cotton, silicone, and foam). Additionally, Principal Component Analysis (PCA) and Maximally Collapsing Metric Learning (MCML) are utilized for visualization of differentiability of commercially available condom brands including Durex™ and Trojan™, and product subtypes. The results present an interesting multi-disciplinary approach of using a direct liquid extraction ambient ionization technique and machine learning to improve the overall workflow for the analysis of lubricants, swabs and fabrics. Machine learning algorithms were able to differentiate between inherent differences of Durex™ and Trojan™ condoms.

Optimization of Mold Powders for High‐Nitrogen Stainless Steel Based on Mold Thermocouple Temperature Variation

High‐nitrogen stainless steel (HNSS) is prone to surface depression during continuous casting; however, its high‐temperature solidification characteristics and mold powder design have not been reported. Based on the analysis of mold thermocouple temperature variation, this study clarifies the high‐temperature solidification characteristics of HNSS and the cause of surface depression. It optimizes the mold powder for HNSS continuous casting according to factory and laboratory research. The factory trials indicate that the mold thermocouple temperature at the corresponding location decreases by 6.0–20.9 °C when the slab surface is depressed. The analysis shows that the high initial solidification strength of HNSS causes its slab surface depressions. Owing to this characteristic, the mold powder for HNSS should have a suitable melting rate, low basicity, and proper Al2O3. This low‐basicity Al2O3‐containing slag has a crystal slag film near the mold side and a thick liquid slag film near the slab. It can both provide good lubrication and control horizontal heat transfer.

Method for Identifying Materials and Sizes of Particles Based on Neural Network

Ships are equipped with power plants and operational assistance devices, both of which need oil for lubrication or energy transfer. Oil carries a large number of metal particles. By identifying the materials and sizes of metal particles in oil, the position and type of wear can be fully understood. However, existing online oil-detection methods make it difficult to identify the materials and the sizes of metal particles simultaneously and continuously. In this paper, we proposed a method for identifying the materials and the sizes of particles based on neural network. Firstly, a tree network model was designed. Then, each sub-network was trained in stages. Finally, the identification performance of several key groups of different frequencies and frequency combinations was tested. The experimental results showed that the method was effective. The accuracies of material and size identification reached 98% and 95% in the pre-training stage, and both had strong robustness.

Dynamic Evolution Characteristics of the Gear Meshing Lubrication for Vehicle Transmission System

The transmission in automobiles is the core component to ensure operational stability. Heat accumulation in the meshing process will reduce the transmission efficiency and affect the service life. Here, the essential physical process to improve transmission heat dissipation is the dynamic evolution process and the thermal transfer characteristics of lubricating oil fields during gear meshing. This paper presents a modeling and solving method for gear meshing lubrication and thermal transfer features based on the volume of the fluid model and piecewise linear interface construction (VOF-PLIC). The dynamic mesh technique combines spring smoothing and reconstruction to optimize the numerical solution process. The dynamic evolution law of gear meshing lubrication and thermal transfer is obtained by analyzing the lubrication evolution process under different speed/steering conditions. The results show that the proposed modeling and solving method could well reveal the lubrication and thermal transfer laws of the gear meshing. The temperature of the gear meshing regions was higher than that in the other regions, and the lubrication temperature showed an increasing linear trend with the stirring process. As the gear speed increased, the meshing resistance moment increased, the transmission power loss increased, and the lubrication oil temperature was larger than that of the gearbox. The power loss under the clockwise rotation of the driving gear G4 was higher than that under the counterclockwise rotation of the driving gear. The relevant results can provide theoretical references for the dynamic analysis of automotive transmission lubrication and technical support for gear profile design and lubrication optimization.

Polydopamine/polyethyleneimine co-crosslinked graphene oxide for the enhanced tribological performance of epoxy resin coatings

• GO were co-crosslinking modified through an environmentally friendly, simple and low-cost process. • Dispersion and surface activity of GO were enhanced by the covalently cross-linked network. • Friction and wear rate of the EP coating reduced by 31.9% and 62.7%, respectively. • Formation of GO lubrication transfer film played the role in friction and wear reduction. To enhance the wear resistance of graphene oxide (GO) nano-filled epoxy resin (EP) coatings with excellent dispersion, GO were modified using a co-crosslinking strategy between polydopamine (PDA) and polyethyleneimine (PEI) through an environmentally friendly, simple and low-cost process. High-density amino-branched PEI and highly adhesive PDA formed covalent bond cross-links with GO (PDA/PEI-GO) through the Michael addition and Schiff base reactions. With the introduction of amino active sites, the PDA self-polymerization reaction time was significantly shorted from 24 h to 6 h. The covalently cross-linked network increased the lamellar spacing of GO and enhanced the interfacial bonds between the PDA/PEI-GO lamellae and EP matrix. Due to the improved dispersion and surface activity of GO, the PDA/PEI-GO nano-filled EP coating exhibited excellent wear resistance. Reciprocating friction with GCr15 stainless steel ball, the average friction coefficient and wear rate of the coating were reduced by 31.9% and 62.7%, respectively, compared to the pure EP coating. In addition, the wear mechanism of the PDA/PEI-GO/EP coating changed from adhesive and fatigue wear to abrasive wear, and it maintained good wear resistance by forming a GO lubrication transfer film on the counterpart surface. Therefore, this study may provide a new strategy for improving the dispersion of graphene in wear-resistant polymer materials for practical applications.

Reproduction of Nanofluid Synthesis, Thermal Properties and Experiments in Engineering: A Research Paradigm Shift

The suspension of different nanoparticles into various conventional thermal fluids to synthesize nanofluids has been proven to possess superior thermal, optical, tribological, and convective properties, and the heat transfer performance over conventional thermal fluids. This task appears trivial but is complicated and significant to nanofluid synthesis and its subsequent utilization in diverse applications. The stability of mono and hybrid nanofluids is significantly related to stirring duration and speed; volume, density, and base fluid type; weight/volume concentration, density, nano-size, and type of mono or hybrid nanoparticles used; type and weight of surfactant used; and sonication time, frequency, mode, and amplitude. The effects of these parameters on stability consequently affect the thermal, optical, tribological, and convective properties, and the heat transfer performance of nanofluids in various applications, leading to divergent, inaccurate, and suspicious results. Disparities in results have inundated the public domain in this regard. Thus, this study utilized published works in the public domain to highlight the trend in mono or hybrid nanofluid formulation presently documented as the norm, with the possibility of changing the status quo. With the huge progress made in this research area in which a large quantum of different nanoparticles, base fluids, and surfactants have been deployed and more are still emerging in the application of these advanced thermal fluids in diverse areas, there is a need for conformity and better accuracy of results. Reproduction of results of stability, thermal, optical, tribological, anti-wear, and fuel properties; photothermal conversion; and supercooling, lubrication, engine, combustion, emission, thermo-hydraulic, and heat transfer performances of formulated mono or hybrid nanofluids are possible through the optimization and detailed documentation of applicable nanofluid preparation parameters (stirring time and speed, sonication duration, amplitude, mode, frequency, and surfactant concentration) employed in formulating mono or hybrid nanofluids. This proposed approach is expected to project a new frontier in nanofluid research and serve as a veritable working guide to the nanofluid research community.

Einfluss des Substratmaterials bei der Transferschmierung von Stahl- Bronze-Kontakten mit PA66-PTFE-cb Trockenschmierstoffen

In this work, the dependence of the friction and wear behaviour in dry-lubricated steel-bronze contact on the dry lubricant used and on the substrate material (steel or bronze) under constant load was investigated. For this purpose, a block two-disc test rig was used, with the dry lubricants PA66-PTFE-cb as blocks, which were produced via chemical bonding (cb) of polyamide 66 (PA 66) and radiation-modified polytetrafluoroethylene (PTFE). The results provide a good basis for the selection of a suitable dry lubricant and the counter body for the transfer of the dry lubricant in dry lubricated worm gears consisting of a steel worm and a bronze wheel.

Coupling of heat transfer and lubrication of cylinder liner-piston skirt conjunction and low-friction temperature strategy of cylinder liner

PurposeThis paper aims to understand the influence of cylinder liner temperature on friction power loss of piston skirts and the synergistic effect of cylinder liner temperature on lubrication and heat transfer between piston skirt and cylinder liner.Design/methodology/approachA method to calculate the influence of cylinder liner temperature on piston skirt lubrication is proposed. The lubrication is calculated by considering the different temperature distribution of the cylinder liner and corresponding piston temperature calculated by a new multilayer thermal resistance model. This model uses the inner surface temperature of the cylinder liner as the starting point, and the starting temperature corresponding to different positions of the piston is calculated using the time integral average. Besides, the transient heat transfer of mixed lubrication is taken into account. Six temperature distribution schemes of cylinder liner are designed.FindingsSix temperature distributions of cylinder liner are designed, and the maximum friction loss is reduced by 34.4% compared with the original engine. The increase in temperature in the second part of the cylinder liner will lead to an increase in friction power loss. The increase of temperature in the third part of the cylinder liner will lead to a decrease in friction power loss. The influence of temperature change in the third part of the cylinder liner on friction power loss is greater than that in the second part.Originality/valueThe influence of different temperature distribution of cylinder liner on the lubrication and friction of piston skirt cylinder liner connection was simulated.

Simulation of Unsteady Flows of Oil/Gas in the Ventless Bearing Chamber of an Aero-Engine

The unsteady motion behavior of oil/gas two-phase flow in a novel ventless bearing chamber has significant impacts on the lubrication and heat transfer efficiency of bearings due to the various advantages of lower pressure levels and weaker rotating airflow effects. In this paper, the unsteady motion behavior of oil/gas two-phase flow in a ventless aero-engine bearing chamber is investigated by three-dimensional numerical simulation through the volume of fluid (VOF) method, and the numerical method is verified using published experimental data. The flow characteristics of oil/gas two-phase in the secondary flow and three-dimensional flow are investigated. The results show the evolution of vortices and the transition of the driving mode in the unsteady motion of oil/gas two-phase flow, and a criterion for the shift of the driving mode at different rotor speeds is proposed. As the rotation speed increases, the variation trend of the velocity field and pressure field of oil/gas two-phase flow is consistent, and the accumulation region of oil becomes inconspicuous. The results indicate a reference for enhancing the performance of lubrication systems for aero-engines.

Research on tribological behavior of graphene with in-situ MgO nanoparticles reinforced AZ91 alloy composite

Magnesium-coated graphene (GNPs) was successfully prepared by a novel organic chemical reduction method with significantly improved wettability and dispersion. The GNPs were uniformly distributed in the matrix, while a finer and more dispersed strengthening phase β-Mg17Al12 was precipitated around it. Moreover, MgO nanoparticles were formed by in-situ reaction on the surface of GNPs, forming nano-scale contact and tight interfacial bonding with the substrate, thereby significantly improving the wear resistance of the composites. The wear mechanism has also changed from severe delamination and abrasive wear to mixed wear of slight delamination, adhesion, and oxidation. The increase in wear resistance is attributed to the combined effect of the lubrication and load transfer of GNPs, the enhanced effect of fine precipitates on the mechanical properties of the matrix, and the synergistic effect of in situ generated MgO nanoparticles against deformation.