Effect Of Solid Lubricants Research Articles

Effect of MoO3 Content on Ni3Al-Ag-MoO3 Composite Coating Microstructure and Tribological Properties

In order to provide effective solid lubrication to Ni3Al coating, 10 wt.% Ag and different amounts of MoO3 solid lubricant were mechanically mixed with the SHSed Ni3Al powder and sprayed HVOF. Microstructure, mechanical properties, and tribological behavior from 25 °C to 800 °C of the coatings were studied, and the basic wear mechanisms were explored and discussed as well. Results show that the hardness and adhesive bonding strength of the coatings are slightly decreased, while there is little effect on the microstructure and mechanical properties of the Ni3Al-based composite coating when the content of MoO3 additive in the feedstock powder is lower than 15 wt.%. The composite coating formed by feedstock powder containing 15 wt.% MoO3 additive also presents excellent anti-friction and anti-wear performance from 25 °C to 800 °C, especially at 800 °C, where a complete, smooth, and thicker lubricating film comprised of NiO, Al2O3, MoO3, and Ag2MoO4 was formed, which reduced the friction coefficient (COF) and wear rate (WR) to the lowest value of 0.36 and 6.03 × 10−5 mm3/(Nm), respectively. An excessive amount of MoO3 in the feedstock powder (20 wt.%) results in inferior interlayer bonding of the formed coating, and the coating is more prone to delamination and abrasive wear above 200 °C.

Investigate the optical and dry sliding wear behavior of solid lubricated sillimanite reinforced aluminum metal matrix composite

The aluminum metal matrix composite (AMC) is prepared by incorporating solid lubricants (Tin, Graphite and both) with 10 wt% sillimanite (Al2SiO5; 20–120 µm; sea beach mineral) as reinforcement. AMC was prepared by the using of liquid metallurgical vortex method (stir casting). Meanwhile, the effect of solid lubrication has also been studied with 3 wt% solid lubricants (Tin, Graphite and both). In the Al-matrix, Al2SiO5 particles were distributed homogenously, according to optical microscopy. As a result of reinforcement addition, primary silicon refinement has also been observed. The wear analysis revealed that sillimanite improved the wear resistance of the composite samples over the base alloy i.e., A390. In this study, the material losses of solid lubricants induced aluminium metal matrix composites are reduced. Further, the wear studies showed that dual solid lubricants had better wear resistance.

Nanoscale MXene Interlayer and Substrate Adhesion for Lubrication: A Density Functional Theory Study.

Understanding the interlayer interaction at the nanoscale in two-dimensional (2D) transition metal carbides and nitrides (MXenes) is important to improve their exfoliation/delamination process and application in (nano)-tribology. The layer–substrate interaction is also essential in (nano)-tribology as effective solid lubricants should be resistant against peeling-off during rubbing. Previous computational studies considered MXenes’ interlayer coupling with oversimplified, homogeneous terminations while neglecting the interaction with underlying substrates. In our study, Ti-based MXenes with both homogeneous and mixed terminations are modeled using density functional theory (DFT). An ad hoc modified dispersion correction scheme is used, capable of reproducing the results obtained from a higher level of theory. The nature of the interlayer interactions, comprising van der Waals, dipole–dipole, and hydrogen bonding, is discussed along with the effects of MXene sheet’s thickness and C/N ratio. Our results demonstrate that terminations play a major role in regulating MXenes’ interlayer and substrate adhesion to iron and iron oxide and, therefore, lubrication, which is also affected by an external load. Using graphene and MoS2 as established references, we verify that MXenes’ tribological performance as solid lubricants can be significantly improved by avoiding −OH and −F terminations, which can be done by controlling terminations via post-synthesis processing.

Study on Friction and Wear Properties of New Self-Lubricating Bearing Materials

In this paper, friction and wear tests were carried out: 45# steel (carbon steel) was rubbed with aluminum bronze, aluminum bronze-based inlaid solid self-lubricating bearing (ISSLB) material, tin bronze, and tin bronze-based ISSLB material under different loads. The friction and wear properties (friction coefficient, wear amount and friction temperature) of the above four materials were studied. The friction and wear properties of the new self-lubricating bearing material and the traditional copper alloy under the same load were compared. The friction mechanism of each material in the friction process was discussed. The effect and mechanism of C-MoS2 composite solid lubricant on friction and wear properties were analyzed. Under the experimental loads of 100 to 500 N, the average friction coefficients of aluminum bronze-based ISSLB material were maintained in the range of 0.18~0.14, while the average friction coefficients of tin bronze-based ISSLB material were maintained between 0.26~0.20, which is much lower than those of copper alloy. The wear amounts of tin bronze-based ISSLB material were always in the range of 14.7~34.4 mg, which were much less than those of aluminum bronze-based ISSLB materials and copper alloy. The results show that the copper-based ISSLB materials possess excellent wear resistance, and the friction and wear properties of tin bronze-based ISSLB material are better than that of aluminum bronze-based ISSLB material. Therefore, if the copper-based ISSLB materials are applied to self-lubricating bearings, the friction and wear resistance of bearings will be greatly improved and the service life of bearings prolonged.

Tribo-mechanical characterisation of MoS2 and H-BN reinforced PA66 composite

ABSTRACT This research aims to create a composite that is inexpensive and can be used in mechanical applications. The main aim is to improve the tribological performance of PA66 by reinforcements. Two fillers were utilised in the experimentation because MoS2 is a remarkably effective solid lubricant in dry conditions, but the results are not the same in high humidity. H-BN is utilised here to get the benefit in both dry and humid environments and to reduce the negative impact of humidity on the tribological performance of composite. Tensile and hardness tests were performed to identify the mechanical properties, while tribological tests on pin-on-disc were performed to analyse the COF and wear rates of materials. SEM, XRD, and DSC characterisations were utilised to analyse the tensile fracture mechanism, crystallinity, and glass-transition temperature of materials, respectively. The result shows that the strength and hardness of the composite increased in a reasonable amount compared to virgin PA66. Wear and COF tests were conducted with three different parameters, and the results showed an improvement in wear rates of composites compared to virgin PA66.

Effects of multi-layer graphene on the fracture toughness and wear resistance of WC-11Co cemented carbide

ABSTRACT The effects of multi-layer graphene (MLG) on the properties of tungsten carbide-11 cobalt (WC-11Co) cemented carbides were studied by transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction analysis (XRD) and other methods. The results show that when the MLG content is 0.1 wt%, the density, hardness and fracture toughness are 3%, 14.5% and 71.8% higher, respectively, compared with the sample without MLG. Bridging and deflection of cracks by MLG improve the fracture toughness of WC-11Co. In addition, MLG inhibits the transformation of the Co phase into Co3C during the sintering process and makes Co phase maintain FCC structure at room temperature, thus enhancing the fracture toughness of the matrix. MLG prevent the matrix from generating W3Co3C and Co3C, thus improving wear resistance. Furthermore, MLG improves the thermal conductivity of cemented carbide and greatly reduces the degree of oxidative wear of the matrix during friction tests. The wear volume of the sample with 0.1 wt% MLG is 98% smaller than that of the sample without MLG, but its mean friction coefficient is 8.8% higher during stable stage. It is because the solid lubricating effect of the wear debris is greater than that of the MLG after 900s.

Optimization of textured parameters to improve the tribological behavior of TC4-based bionic coating using RSM

Inspired by the surface texture of bivalve shell, the bionic wavy grooves were designed and prepared on the bionic coating of TC4 using laser marking technology. Response surface method was used to optimize the parameters of bionic texture structure for improving the tribological behavior. Influence of coupling mechanisms of bionic coating and texture on the tribological performance of TC4 alloy were investigated. The results show that the bionic wavy grooves reduce the fluctuation of loading force. The coupling of bionic texture and coating breaks the continuity of coating interface, and the peeling wear debris are easily captured by the bionic wavy grooves. The repairing effect of solid lubricant is increased, thus the complete lubrication film is easier to be formed on the worn surface during the sliding process.

Adhesive wear performance of self-lubricating functionally graded cemented tungsten carbide prepared by spark plasma sintering

In order to encourage environment friendly manufacturing, dry machining is extensively explored and acknowledged. Consequently Functionally Graded Cemented Tungsten Carbide (FGCC) with solid lubricant was prepared by Spark Plasma Sintering at different heating rate and sintering temperature. The wear behavior of developed materials was explored by pin-on-disc tribological tests and dry machining. The attempts were made to analyze effect of key test parameters (such as load, ambient temperature, and sliding velocity) and solid lubricant over tribological behavior. The presence of solid lubricant resulted in reduced coefficient of friction (COF) and wear. The ambient temperature and load were displayed most significant influence over wear and COF respectively. Also samples prepared at high sintering temperature as well as heating rate demonstrated lower wear and COF. Additionally, the primary failure mechanism was identified as binder removal. These tribological examinations confirmed the suitability of self-lubricating FGCC as a cutting tool material for dry machining.

Fabrication and electrical sliding wear of graphitic Cu–Cr–Zr matrix composites

Abstract The present work was undertaken to prepare graphitic Cu–Cr –Zr matrix composites in order to develop new materials for application under sliding contact in an electrical field. The electrical sliding wear behavior of the graphite (Gr)/CuCrZr composite was investigated from a microstructural viewpoint, compared with the matrix alloy. The results indicate that by using the water atomized Cu–Cr–Zr powder and copper-coated graphite particles as starting materials, compact and homogeneous microstructure can be obtained in the composites. Fine and coherent particulate precipitations are formed in the Cu–Cr–Zr matrix during the aging treatment process, which help to improve the mechanical properties. Under the electrical sliding wear condition, incorporation of graphite in the Cu–Cr–Zr matrix not only decrease the wear loss of the sliding pair but also maintain steady-state friction coefficient. The main reason is that the graphite film that smears on the contacting surfaces can alleviate materials loss induced by electric arc discharge and adhesion wear. Proper aging treatment helps to make full use of the solid lubricant effect of the graphite particles.

УПЛОТНИТЕЛЬНЫЕ МАТЕРИАЛЫ НА ОСНОВЕ ПОЛИТЕТРАФТОРЭТИЛЕНА ДЛЯ АВИАЦИОННОЙ ТЕХНИКИ

The paper studies the effect of mechanically activated serpentine and magnesium spinel on the deformation-strength and tribotechnical characteristics and structure of polytetrafluoroethylene (PTFE). It has been determined that with the simultaneous introduction of fillers, an increase in wear resistance is observed up to 1125 times while maintaining and even slightly increasing the deformation and strength characteristics of the PTFE. It has been concluded that filler particles contribute to a change in the supramolecular structure of the PTFE, and also affect the formation of a protective secondary structure on the friction surface with the effect of solid lubrication. The developed materials can be used as parts of pneumatic-, hydro- and fuel systems for arctic and aviation equipment.

Effect of MoS2 solid lubricant on the tribological aspects of Ti-6Al-4V alloy in drilling operations

Ti-6Al-4 V poses significant wear challenges to the tool due to its low thermal conductivity and tensile strength. Tools with Ti-6Al-4 V are exposed to extreme temperatures and mechanical stresses, making them prone to wear.Machining produces high cutting forces during drilling operations; thus the cutting edges are subjected to high stresses. Tools with high levels of elevated-temperature, hardness and heat resistance are well suited to this type of machining. Researchers have tried several synthetic coolants to resolve this problem, but all have been found to be either ineffective or harmful to the environment. This study explored tribological behavior using cottonseed oil and cottonseed oil plus fine MoS2 particles. At an extent of 10 and 20% were mixed with Cottonseed oil and disseminated at the cutting zone. The best lubricating properties were obtained in the MQL condition with cottonseed oil containing 20% MoS2. Molybdenum disulphide (MoS2) far exceeded expectations in terms of surface finish, tool wear, micro-chipping, abrasive wear, and material adhesion. It was found that the combination of feed rate and cutting speed make MoS2 produce good machining characteristics. Using SEM, surface roughness, hardness, and chip thickness, the performance of two different lubricant mixtures was assessed.

Impact of spark plasma sintering process on tribo surface of Al/CNT composites

Spark Plasma Sintered Aluminium (SPSed Al) composites are widely used in various micro components of the engineering applications. This paper deals with the evaluation of tribological behavior of the SPSed Al composites with respect to the SPS process parameters. The multi-walled Carbon Nano Tubes (CNTs) are added to the SPSed Al composites to improve its wear resistance by a solid lubrication effect. The presence and distribution of CNT over the Al matrix are confirmed through the FESEM analysis and the crystallographic changes of the SPSed Al/CNT composites are examined using the XRD analysis. The hardness of the SPSed Al/CNT composite has been improved by the re-crystallization at the optimal SPS condition. It also influences the frictional wear behavior of the Al/CNT composites and it resulted in overcome of ploughing on the Al surface. The frictional wear behavior of the SPSed Al/CNT composites is optimized using the taguchi methodology and the minimum wear rate of 24.7 × 10–6 g m−1 and the CoF of 0.192 are obtained for the Al/CNT1 wt% composite sintered at 500 °C and ball milled at 300 rpm for 480 min. The worn surface of the Al/CNT1 wt% composite reveals that the mild abrasive wear is occurred at the optimal tribo condition.

Tribological properties and self-compensating lubrication mechanisms of Ni3Al matrix bio-inspired shell-like composite structure

Composite surface structures inspired by biological characteristics have the potential to strengthen the synergistic effects of surface micro-textures and solid lubricants by improving their tribological properties. This investigation sought to discuss the lubrication mechanisms by designing bio-inspired shell-like Ni3Al matrix composite surface structure, in which an ordered patterning composite (OPC) structures contained Ni3Al matrix and solid lubricants Sn-3.0Ag-0.5Cu(SAC305) alloys. Reciprocating dry sliding tests of OPC structures with different surface texture densities against high-carbon steel balls were performed, and the results were compared to those for orderly pattern (OP) structures without the SAC305 alloy. The results showed that the appropriate volume fraction of the SAC305 alloy should further promote decreases in the friction coefficients and wear losses. This could be attributed to the self-compensating lubrication behaviors of the SAC305 alloy. It formed a lubricating film with a certain area and thickness, which should be controlled by the material properties and components of the bio-composite surface structures, as well as the surface texture density. Additionally, methods based on a combination of theoretical models and experimental measurements further confirmed that the soft and hard materials of the OPC structure played different roles. The soft material (SAC305 alloy), which had a high surface energy and low hardness, had a better material transfer tendency than the hard material (Ni3Al matrix), which had a low surface energy and high hardness. This resulted in the formation of a transfer film and the occurrence of self-compensating lubrication behaviors.

Improved load-bearing capacity of Mo-doped Ti-N coatings: Effects of Mo alloying and GB plasticity

Deformation mechanisms especially grain boundary(GB)-related plastic behaviors are essential for understanding and designing advanced hard coatings. This work systematically studied mechanical behaviors and the underlying interfacial mechanisms in Ti-Mo-N coatings, which is predicted to have both high hardness and toughness according to first-principle calculation. Mo-doped TiN coatings were prepared by multi-arc plating technique as a function of N 2 pressure. The as-deposited coatings demonstrate a bct-Ti 2 N + fcc-TiN dual-phase structure below 1.2 Pa, and single-fcc structure at above 1.2 Pa. Single-fcc phase Ti-Mo-N coatings show considerable higher hardness and load-bearing capacity compared to pure TiN coating due to alloying effect of Mo. Transmission electron microscope (TEM) study unveil that GB plays the key role in the deformation behaviors. The Mo-doped TiN coatings exhibit enhanced plastic deformation ability of GBs, including substantial plastic flow and twinning, which retard intergranular cracking that is geometry necessary during GB glide and rotation. While the appearance of the bct -Ti(Mo) 2 N phase leads to stress concentration at bct-fcc interface during deformation because of the large lattice misfit, considerably lowering load-bearing capacity. In addition, Ti-Mo-N coatings have lower friction coefficient (COF) and wear rate than TiN coating in reciprocal tribology tests, which is attributed to the higher hardness and toughness, as well as tribochemistry-induced solid lubricant effect. • Mo doping results in substantial hardening-toughening effect. • GB plastic behaviors play the critical role. • Enhanced GB plasticity leads to high load-bearing capacity. • bct-fcc interfaces cause stress concentration and embrittlement.

Effects of solid lubricants on the tribological behavior of steel‐backed UHMWPE fabric composites

AbstractAboard ship, the use of lubricating oil in mechanical equipment is sometimes difficult to achieve and applied oil can easily leak. The use of self‐lubricating materials can largely solve this problem. In this study, three kinds of solid lubricant‐enhanced 304 stainless steel‐backed ultrahigh molecular weight polyethylene (UHMWPE) fabric composites were fabricated with the addition of graphite, molybdenum (IV) disulfide, or polytetrafluoroethylene (PTFE). They were tested under various rotating speeds and compared with pure steel‐backed UHMWPE fabric composites. The tribological performance of these composites was evaluated by analysis of friction coefficient, wear rate, and worn face morphology. The results showed that PTFE‐enhanced composites exhibited the best friction reduction performance under all test conditions, better antiwear ability at rotating speeds under 200 rpm, and optimized wear surface morphology, thus indicating better synergy between PTFE and UHMWPE fabric.

Superior lubrication and electrical stability of graphene as highly effective solid lubricant at sliding electrical contact interface

Graphene with excellent mechanical, tribological and electrical properties has enormous potential as solid lubricant at sliding electrical contact interfaces. Here, ultra-low friction (the coefficient of friction is about 0.028), ultra-high current stability (the coefficient of variation is as low as 4.74%) and effective wear-resistance properties (keep stable under contact pressure of 5.93 GPa for 10,000 cycles) of graphene as solid lubricant are found at electrical contact interface under the combined effect of the load and current. The high current stability and ultra-low friction could attribute to stable electric contact and conductive quality at the interface due to the high flexibility and carrier mobility of graphene based on the molecular dynamic simulations and atomic stick-slip behavior calculations. The high wear resistance at sliding electrical contact interface derives from the ultra-strong mechanical strength of graphene for combined effect of electricity and load. Our studies found that graphene with ultra-low friction, ultra-high conductivity, flexibility, and mechanical strength is unique as solid lubricant in various devices with sliding electrical contact interfaces.

Employment of Micro- and Nano-WS2 Structures to Enhance the Tribological Properties of Copper Matrix Composites

Friction and wear are responsible for around 23% of the energy consumption in transportation, manufacturing, power generation, and residential sectors. Employed components are exposed to a wide range of operational conditions, therefore a suitable material design is fundamental to decreasing tribological issues, energy consumption, costs, and environmental impact. This study aims to analyze the effect of different solid lubricants on the suitability of copper matrix composites (CuMCs) as a potential solution to reduce the depletion of sliding electrical contacts working under extreme conditions. CuMCs samples are produced by cold-pressing and sintering to merge a high electrical conductivity with the lubricant effect supplied by different species, namely tungsten disulfide micro-powder (WS2), inorganic fullerene-like (IF) tungsten disulfide nanoparticles, and graphene nanoplatelets (GNP). The crystalline structure of the pristine and composite materials is characterized via XRD. The electrical tests show a small decrease of conductivity compared to pure copper, due to the insulating effect of WS2; however, the measured values are still adequate for conduction purposes. Micro-scratch and wear tests highlight the positive effect of the combination of WS2 structures and GNP. The friction coefficient reduction leads to the possibility of extending the lifetime of the components.

Effects of solid graphite lubricants for powder compaction

ABSTRACT In this paper, the mechanical characteristics for metal powder compaction with the addition of graphite powders are investigated to reduce the friction generated during the powder compaction process. The discrete element method model is developed for powder compaction with powder mixture containing steel-graphite and copper-graphite. Compaction experiments are performed for the validation of the model. Parameters involved with mixing conditions such as graphite mixing and graphite size ratio and its effects on compressive characteristics are explored. Optimal values for mixing conditions are defined. Also, the effects of powder mixing parameters are investigated through analysing stress transfer ratio from top to bottom punch and compressive force distribution throughout the powder compact. Significant improvements in mechanical properties are observed with the addition of graphite lubricants. Improved stress transfer rate by 57% (steel) and by 44% (copper) are obtained and decreased standard deviation of compressive force by 85% (steel) and by 67% (copper) are observed.

Effect of microstructure and mechanical properties on the tribological and electrochemical performances of Si/DLC films under HCl corrosive environment

Si-doped diamond-like carbon (Si/DLC) films appear very attractive due to their superior mechanical and tribological properties and chemical inertness. In the present work, Si/DLC films with silicon concentration from 1.64 to 15.32 at.% were fabricated on 304 stainless steel by adjusting Si target current using unbalanced magnetron sputtering system. The microstructure, surface morphology and mechanical properties of the films with different Si concentration, as well as the tribological and electrochemical properties of the films under HCl corrosive environment were systematically investigated. Results showed that Si doping increased the sp3 CC content, hardness, and elastic modulus of as-fabricated films, lowered the residual stress, but deteriorated the adhesion strength. At the same time, the appropriate Si concentration was conducive to low surface roughness and dense microstructure. The Si/DLC films presented good tribological performances in 1 M HCl solution, including low friction coefficient and wear rate. The degradation of tribological properties was attributed to the synergistic effect of less solid lubrication, declined adhesion strength, worse resistance to elastic and plastic deformation. The wear mechanism was mainly dominated by abrasive wear. Furthermore, the Si/DLC film with 15.32 at.% Si provided the best corrosion resistance, which benefited from its dense structure, higher thickness, and the highest sp3 CC content.

Noise Reduction Mechanism and Analysis of TC4 with Dimple Textured Surfaces

Improving the friction-induced noise suppression performance of TC4 has far-reaching significance for its wide application in the field of robots and semiconductors. The friction noises of TC4 with solid lubricant (Sn-Ag-Cu) filled into dimples (TCS) and TC4 were predicted by simulation analysis. The noise reduction performance of TCS during dry rotary sliding was discussed. TCS with dimple size of 0.6 mm (TCS-0.6) exhibited the prominent performance of noise reduction, which was attributed to the synergistic effect of dimples and solid lubricant. During the dry sliding process, the debris were contained by dimples, the stress distribution in matrix was modified by lubricant, and the defects were decreased. Hence, the roughness of worn surface was reduced, which was beneficial to obtaining the stable friction coefficient. Inhibiting the unstable vibration by controlling the friction coefficient of the system can effectively demote the friction-induced noise.