Friction Coefficient Resistance Research Articles

Tribological Characteristics of Fe-Cu-Sn Alloy with Molybdenum Disulfide as a Solid Lubricant under Dry Conditions

Fe-based materials play a significant role in engineering applications as bearings and gears owing due to their low cost, ease of manufacture, high strength, availability, and good wear resistance and low coefficient of friction. In this study, molybdenum disulfide added Fe-Cu-Sn alloy is developed using simple single stage compaction and sintering elemental powders. The friction and wear behaviors of the sintered alloys sliding against EN8 steel ball under dry conditions were studied using a ball-on-disc tribometer. The interconnected porosity decreases and density increases with added molybdenum disulfide. The hardness of the molybdenum disulfide added compositions are better than the base composition. The composition with higher wt% of molybdenum disulfide is found to be beneficial in improving friction and wear characteristics. The wear mechanism in base composition is observed to be adhesive and abrasive, while as mild abrasive wear is observed in the 3 wt% molybdenum disulfide added sample.

Analysis of natural circulation frictional resistance characteristics in rod bundle channel

A considerable amount of research has gone into understanding the thermal-hydraulics characteristics of rod bundle channels which is of great importance for the nuclear industry. This paper will show that the development of the correlation of the frictional resistance coefficient in rod bundle channels under natural circulation conditions is well understood. This paper presents experimental studies of the single-phase resistance and obtains an improved correlation of the frictional resistance coefficient under natural circulation conditions based upon thermal-hydraulics characteristics which are well understood. It is also shown that this newly developed correlation closely predicts data.The experimental results show that the frictional resistance coefficient of a rod bundle channel under natural circulation is related to the physical properties of fluid and the size of the rod bundle channel. According to different flow regions, the relationship between the frictional resistance coefficient and Reynolds number is discussed separately, and the expressions of frictional resistance coefficient with Reynolds number in laminar flow region and transition region are obtained. After considering the influence of fluid properties on the frictional resistance coefficient, this paper introduces the kinematic viscosity correction factor to correct the frictional resistance coefficient. Finally, the complete expression of the frictional resistance coefficient was obtained. This newly developed predictive expression is in good agreement with experimental data in both the laminar and transition flow regions, with a relative error within ±5%. Thus we now have a predictor of the frictional resistance coefficient under natural circulation conditions based upon more complete thermal-hydraulic parameters in a static state.

Identifying the significance of Sn addition on the tribological performance of Ti-based bulk metallic glass composites

Tailoring the properties of an engineering material with low coefficient of friction (COF) and high wear resistance has been a long goal in the tribological research. It is particularly true for the bulk metallic glass composites (BMGCs), which are promising for a large range of advanced applications. Although the materials design and mechanical properties have been extensively investigated, knowledge of their tribological behaviors is still lacking. Ball-on-block wear tests were thus conducted to investigate the effect of Sn addition on the tribological behaviors of Ti45Zr25Nb6Cu5Be17 BMGCs under different normal loads. Nano-indentation and nano-scratch tests were carried out to study the phase-specific wear properties of the crystalline dendrite and amorphous matrix in BMGCs respectively. Preferred wear and delamination in the dendrite phase as a result of the plastic mismatch between the two constituent phases is responsible for the abrasive wear in the Ti47Zr25Nb6Cu5Be17 and Ti46Zr25Nb6Cu5Be17Sn1 BMGCs. While, mechanically driven tribolayer during sliding enables oxidative wear and improved tribological properties in the Ti45Zr25Nb6Cu5Be17Sn2 BMGC. Based on the synergistic mechanical and chemical effects, the underlying relationship between the intrinsic dendrite properties and the wear behaviors of BMGC was revealed.

Friction and Mechanical Properties of Highly Filled Polybenzoxazine Composites: Nanosilica Particle Size and Surface Treatment

AbstractFrictional and mechanical properties of highly filled polybenzoxazine [poly(BA‐a)] composites which are influenced by nanosilica contents, particle sizes, and surface treatments are investigated. The coefficient of friction and wear resistance, storage moduli, and microhardness of the nanosilica‐filled poly(BA‐a) composites systematically increase with an increase of nanosilica content, while those values of the nanocomposites are improved with decreasing particle sizes at the equivalent nanosilica content. The modulus can be predicted by the Kerner model with the maximum packing fraction, while the microhardness of the nanocomposites is in agreement with the Halpin–Tsai model. The nanocomposites fabricated with untreated nanosilica particles exhibit higher frictional and mechanical properties when compared with the surface‐treated nanocomposites at the equivalent particle sizes. The interfacial interactions via covalent bond formation between the nanosilica and the poly(BA‐a) are determinative factors for the nanocomposite properties. Highly filled nanosilica‐poly(BA‐a) composites can be employed in various applications where wear‐resistance plays an important role.

Effect of thermal aging on mechanical and tribological behaviors of short glass fiber–reinforced PA66

The use of polyamide (PA) composites in a variety of thermal conditions can enormously affect their durability that is a very important issue for designers and users. In this study, mechanical and tribological behaviors of PA66 reinforced by various weight fractions of short glass fiber were investigated. All studied materials were subjected to accelerated thermal aging tests. Three-point bending flexural tests were carried out to determine the mechanical behavior. Reciprocating tribotester was employed to determine friction and wear behaviors. Tribological tests were carried out without lubrication and under ambient conditions. Ball on flat contact configuration was adopted for friction tests. Wear tests were carried out against an abrasive counterface. Results showed that flexural strength and elastic modulus increased when increasing glass fiber rate for all tested materials. In the contrary, coefficient of friction and wear resistance decreased. Results showed that the thermal aging increased the flexural features and reduced the coefficient of friction. The effect of thermal aging on the wear resistance depends on the reinforcement rate.

Influence of cenosphere on tribological properties of short carbon fiber reinforced PEEK composites

ABSTRACTThis investigation focuses on the effects of cenosphere fillers on tribological properties of carbon fiber reinforced PEEK composites. Dry sliding wear behavior of 15 wt % short carbon fiber (SCF) reinforced PEEK composites filled with 5, 10, 15, and 20 wt % cenosphere was reported in this study, pure PEEK and 15 wt % SCF reinforced PEEK composites were also prepared for comparative analysis. Friction and wear experiments were conducted on a ring‐on‐block apparatus under different loads (100–400 N). The experimental results showed that all the composites exhibited lower coefficient of friction and better wear resistance than the matrix resin under different load conditions. It is noted that 10 wt % of the cenosphere particles filled SCF reinforced PEEK composites show superior tribological properties when compared to the other composites in this study. The morphologies of the worn surface and the fracture surface were analyzed by scanning electron microscopy and the transfer film was observed by optical microscope to understand the dominant wear mechanisms. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47245.

Wear characteristics of sintered AA2014 with alumina and titanium di-Boride metal matrix composites

ABSTRACT The present research work deals with the fabrication of the AA2014 aluminum alloy and two aluminum metal matrix composites such as composite-I (95 wt % AA2014 + 5 wt% of Al2O3) and composite-II (95 wt % AA2014 + 5 wt% of TiB2) through the powder metallurgy route. Elemental powders of the AA2014 aluminum alloy, composite-I and composite-II were compacted at a pressure of 350 ± 10 MPa using the universal testing machine and sintered at 610 ± 10° C for 2 h in a vacuum hot press under nitrogen atmosphere. Compositions were considered for micro structural, density, porosity, mechanical properties and wear analysis. Microstructural analysis reveals the uniform distribution of reinforcement particle with cluster formation. In the density analysis, the sintered AA2014 aluminum alloy has exhibited 95% of its theoretical density. The AA2014 aluminum alloy shows less porosity compared with composite-I and composite-II. Composite-II exhibits higher wear resistance and lower coefficient of friction which will lead to cost saving and increases engine efficiency.

Effect of Coating Thickness on Wear Performance of Inconel 625 coating

INCONEL® nickel-chromium alloy 625 is widely used for its high strength, excellent corrosion resistance and creep resistance on prolonged exposure to aggressive environment. However, despite its properties and industrial application, its wear resistance is not entirely satisfactory. The article investigates and presents the tribological performance of Inconel 625 coating using reciprocating scratch test. High velocity oxyfuel (HVOF) method was used to deposit Inconel 625 film onto 304 stainless steel surfaces. The frictional behavior and wear data were studied in order to observe the effect of coating thickness on wear failure. The results revealed that coatings of higher thickness showed lower coefficient of friction, better adhesion and good wear resistance in comparison to the low coating thickness.

Research on micro-deep drawing process of concial part with ultra-thin copper foil using multi-layered DLC film-coated die

During the miniaturization of specimen size, lubrication plays a very important role in microforming process. Size effect of friction occurs clearly when a kind of liquid lubricant is applied, and the ultra-thin sheet is easily thinned and even broken in micro-deep drawing. Diamond-like carbon film (DLC film) gains more and more attention for its advantages such as low coefficient of friction and high wear resistance. In the investigation, functionally graded multi-layered DLC films were deposited on die surface by plasma ion implantation. The properties of DLC films were studied by atomic force microscopy, Raman spectroscopy, nano-indentation test, and ball-disc test. It was found the DLC film prepared at voltage of 13.5 kV owns low friction coefficient and high wear resistance. Then, surfaces of punch for deep drawing and female die were modified by depositing functional-graded multi-layered DLC film with a voltage of 13.5 kV. Micro-deep drawing tests were performed, and the distribution of thickness etc. was analyzed. As a result, micro-concial parts with good surface quality and uniform distribution of thickness were obtained. This means that multi-layer DLC film is helpful for improving the quality of ultra-thin sheet part.

Comparison of chromium carbide thin films grown by different power supply systems

The potential use of chromium carbide thin films has been a great interest to academia and industry due to their outstanding properties such as chemical stability, low coefficient of friction, adequate hardness and high wear resistance. In this study, the chromium carbide thin films were fabricated by a magnetron sputtering using different power supply systems, including direct-current (DC), pure high power impulse magnetron sputtering (HiPIMS), and superimposed HiPIMS- middle frequency (MF). The Cr target poisoning status was controlled using a plasma emission monitoring (PEM) system by adjusting the gas flow ratios of Ar and acetylene (C2H2). The morphology and microstructure of thin films were evaluated by scanning electron microscope (SEM) and transmission electron microscope (TEM). The crystallinity of films was studied using an X-ray diffractometer (XRD). The electron probe micro analyzer (EPMA) and X-ray photoelectron spectroscope were used to determine the chemical compositions and binding structures of thin films, respectively. The hardness and residual stress were explored. The results showed that the thin film sample prepared by the superimposed HiPIMS-MF power supply can obtain the maximum hardness of ~27.5 GPa at a PEM set point of 30%, i.e., the target poisoning degree of 70%. The hardening mechanism may be caused by the formation of nanoscale CrC crystallites incorporated into the amorphous CrCx matrix in the thin film, which can be attributed to the Hall-Petch strengthening effect.

Friction Performance of BCG-CO2 Fracturing Fluid for Shale Gas

BCG-CO2 fracturing fluid system is especially suitable for shale gas stimulation with advantage of minimizing the actual water consumption, reducing the damage to formation, recovering more rapidly and efficiently, etc. A major objective of this article is to ascertain the friction performance of BCG-CO2 fracturing fluid in a wide range of experimental conditions for guiding the selection of fracturing parameters. The experimental results showed that the frictional resistance coefficient levels off under the flow velocity greater than 1 m/s. For the impact of the foam quality on the friction resistance coefficient, the completely opposite change rule is showed under foamed and unfoamed conditions.

Experimental study of tribological and mechanical properties of TiN coating on AISI 52100 bearing steel

The surface coating is one of the novel approaches to enhance the performance and durability of the mechanical components by decreasing the wear and friction among two interacting bodies. In this study, tribological and mechanical properties of titanium nitride (TiN) coatings were investigated on the AISI 52100 bearing steel deposited by low-temperature physical vapor deposition system. Surface morphology and elemental composition of the TiN coating were analyzed by scanning electron microscope and energy-dispersive X-ray spectrum, respectively. Substrate surface roughness and coating thickness of TiN were varied for correlative analysis among adhesion, mechanical, and tribological properties. Scratch and tribo tests were performed for evaluating the adhesion and tribological properties, respectively. Samples having the substrate surface roughness (0.2 ± 0.05 µm) and the coating thickness of more than 2.83 µm presented relatively better adhesion, wear resistance, and lower coefficient of friction of the TiN coating.

Potential use of fly ash and bagasse ash as secondary abrasives in phenolic composites for eco-friendly brake pads applications

Brake pad is the essential component of disk brake in automotive applications that is made of phenolic-based composites. The alumina and silica are often used as primary abrasives in brake pads. In this study, we investigated the hardness, compressive, friction and wear properties under room temperature and elevated temperatures (100°C and 150°C) of phenolic-based composites containing the natural ashes of fly ash and bagasse ash as secondary abrasives, which ranged from 0 to 12 wt%, for replacing primary abrasives. The results suggested that 4 wt% secondary abrasives was recommended for optimization of the overall properties of the composites. It was found that all composites exhibited the abrasive wear behavior evidenced by wear debris between the counterfaces acting as third-body abrasives. The phenolic-based composites at 100°C and 150°C had higher coefficient of friction and lower wear resistance than those at room temperature. The incorporation of bagasse ash resulted in more compression for a given load than that of fly ash. In summary, the fly ash and bagasse ash, which were natural ashes, showed a potential use as secondary abrasives in the phenolic-based composites for eco-friendly brake pads.

Viscous flow simulations at high Reynolds numbers without wall functions: Is [formula omitted] enough for the near-wall cells?

The Reynolds-Averaged Navier Stokes equations supplemented by eddy-viscosity models are still the most common mathematical model for the simulation of wall-bounded viscous flows at high Reynolds numbers. Viscous flow simulations around complex geometries are more accurate with the direct application of the no-slip condition at walls, i.e. avoiding the use of wall functions. Determination of the shear-stress at the wall from its definition requires the use of near-wall cells which are typically requested to present a non-dimensional height of y+≃1. However, the effect of this widespread rule of thumb on the numerical accuracy of the solutions has not been established and it may be dependent on the turbulence model choice.In this paper, we discuss the numerical accuracy of viscous flow simulations performed with a RANS solver supplemented by three eddy-viscosity models in the calculation of statistically steady, incompressible flows: the one-equation model of Spalart & Allmaras and the two-equation models SST k–ω and k–kL. The selected test cases are: a flat plate at Reynolds numbers Re equal to 107, 108 and 109; the NACA 0012 airfoil at angles of attack of 0, 4 and 10 degrees with Re=6×106 and the KVLCC2 tanker at model and full scale Reynolds numbers, Re=4.6×106 and Re=2.03×109. Calculations are performed in sets of geometrically similar grids with different sizes of the near-wall cells height to assess the influence of this choice on the numerical uncertainty of the solutions.The results show that the numerical accuracy of the simulations is dependent on the selected turbulence model. For y+<1, there is no significant effect of the near-wall cell height on the numerical uncertainty of the selected flow quantities for the Spalart & Allmaras and k–kL models and so y+≃1 is sufficient to obtain numerical uncertainties of friction resistance coefficients smaller than 1% . On the other hand, with the SST k–ω model, y+≃1 leads to numerical uncertainties of friction resistance coefficients larger than 5% for all the present test cases. To attain the same uncertainty of the other turbulence models with the SST k–ω, one must use y+≃0.1.

Methods of Determination of Frictional Resistance for Prediction of Total Resistance of Inland Waterway Vessels

Abstract In the present paper presented are the results of prediction of total resistance of inland waterway vessels based on model test data. In scaling the resistance from model to full scale the extrapolation with two-dimensional frictional resistance formulation (without form factor) was applied, combined with different methods of determination of frictional (viscous) resistance coefficient. There were used the equations that include the effect of water depth, with and without account for pressure gradient. It was shown that limited depth of water substantially affects the frictional resistance. The results of example calculations are compared to resistance prediction made using the ITTC 1957 model-ship correlation line. Example calculations take into account the limited depth of water. Depending on the applied method of determination of frictional resistance coefficient the resultant total resistance of inland waterway vessel is higher or lower than the resistance based on the ITTC 1957 correlation line. The effect of water depth depends on the ratio of water depth to ship draught (h/T), on ship speed, and on the composition of a convoy. The extrapolation of resistance was made without including the form factor. Computations are made based on model test data for an inland waterway cargo vessel, for a kombi-type convoy of an inland waterway cargo vessel and a dumb barge, and for a convoy of two dumb barges without a pushboat.

Evaluation of Tribological Properties of Thermally Sprayed Copper and Copper Alloy Coatings

Thermally sprayed copper and copper alloy coatings are among the most widely used coating materials for several industrial and medical applications to serve various functions such as corrosion resistance, wear resistance and antibacterial coating applications. In the present study, wear behavior of twin arc spray Cu, Cu 4%Sn (tin bronze), Cu 17%Ni 10%Zn (German silver) and Cu 17%Al 1%Fe (aluminum bronze) coatings is investigated experimentally. Wear tests were conducted using ball-on-disk configuration against a 440C stainless steel ball as a counterface. The effect of normal load on the coefficient of friction and wear behavior was investigated. SEM and 3D optical profilometry were used to characterize the coatings in terms of morphology and surface roughness. It is observed that copper coatings with aluminum and tin bronzes have high wear resistance and low coefficient of friction among the tested coatings, mainly due to their high hardness and coherent splats. It was also found that wear rate increases with the normal load.

Metallic Glasses as Potential Reinforcements in Al and Mg Matrices: A Review

Development of metal matrix composites (MMCs) with metallic glass/amorphous alloy reinforcements is an emerging research field. As reinforcements, metallic glasses with their high strength (up to ~2 GPa) and high elastic strain limit (~2%) can provide superior mechanical properties. Being metallic in nature, the glassy alloys can ensure better interfacial properties when compared to conventional ceramic reinforcements. Given the metastable nature of metallic glasses, lightweight materials such as aluminum (Al) and magnesium (Mg) with relatively lower melting points are suitable matrix materials. Synthesis of these advanced composites is a challenge as selection of processing method and appropriate reinforcement type (which does not allow devitrification of the metallic glass during processing) is important. Non-conventional techniques such as high frequency induction sintering, bidirectional microwave sintering, friction stir processing, accumulative roll-bonding, and spark plasma sintering are being explored to produce these novel materials. In this paper, an overview on the synthesis and properties of aluminum and magnesium based composites with glassy reinforcement produced by various unconventional methods is presented. Evaluation of properties of the produced composites indicate: (i) retention of amorphous state of the reinforcement after processing; (ii) significant improvement in hardness and strength; (iii) improvement/retention of ductility; and (iv) high wear resistance and low coefficient of friction. Further, a comparative understanding of the properties highlights that the selection of the processing method is important in producing high performance composites.

Non-parametric wall model and methods of identifying boundary conditions for moments in gas flow equations

In this paper, we use the molecular dynamics simulation method to study gas-wall boundary conditions. Discrete scattering information of gas molecules at the wall surface is obtained from collision simulations. The collision data can be used to identify the accommodation coefficients for parametric wall models such as Maxwell and Cercignani-Lampis scattering kernels. Since these scattering kernels are based on a limited number of accommodation coefficients, we adopt non-parametric statistical methods to construct the kernel to overcome these issues. Different from parametric kernels, the non-parametric kernels require no parameter (i.e. accommodation coefficients) and no predefined distribution. We also propose approaches to derive directly the Navier friction and Kapitza thermal resistance coefficients as well as other interface coefficients associated with moment equations from the non-parametric kernels. The methods are applied successfully to systems composed of CH4 or CO2 and graphite, which are of interest to the petroleum industry.

Tribological behavior of electroless Ni–B–W coating at room and elevated temperatures

Sodium borohydride reduced electroless Ni–B coatings possess high hardness, wear resistance, and low coefficient of friction. They are found to be suitable candidates for wear reduction of mechanical components. In a quest to achieve enhanced tribological behavior and high thermal stability, the present work reports the inclusion of W to Ni–B coatings. Electroless method is employed for Ni–B–W coating deposition on AISI 1040 steel specimens. Post deposition, the coatings are heat treated at 350 ℃, 400 ℃, and 450 ℃. Deposit characterization is carried out using energy-dispersive X-ray analysis, X-ray diffraction, and scanning electron microscopy. Inclusion of W leads to an increase in microhardness and thermal stability of Ni–B coatings. The tribological behavior of as-deposited and heat-treated Ni–B–W coatings are investigated at room and elevated temperatures (100 ℃, 300 ℃, and 500 ℃). Heat-treated coatings show lower wear rate at room temperature compared to as-deposited ones but the coefficient of friction increases. Tribological test results at elevated temperatures suggest an improvement in the wear resistance and coefficient of friction at 300 ℃ and 500 ℃ in comparison with 100 ℃. Phase transformation study post wear test indicate microstructural changes in the coating due to the in situ heat treatment at high temperature. The tribological behavior of the coatings at 100 ℃ and 300 ℃ is mainly governed by the loose wear debris and formation of debris patches, respectively. Whereas at 500 ℃, formation of protective tribo-oxide patches is also observed.

Wear and friction characteristics of electroless Ni-B-W coatings at different operating temperatures

Sodium borohydride reduced electroless nickel alloy coatings have high wear resistance and low coefficient of friction. The present work investigates the deposition and tribological behavior of a ternary variant of the borohydride reduced coating i.e. Ni-B-W. Electroless Ni-B-W coatings were deposited on AISI 1040 steel substrates. In order to improve the mechanical properties of the deposits, they were heat treated at 350 °C for 1 h. The coatings in their as-deposited and heat treated conditions were characterized by scanning electron microscope, energy dispersive x-ray analysis and x-ray diffraction techniques. Ni-B-W coatings are amorphous in their as-deposited state while they become crystalline on heat treatment. In fact a high microhardness of Ni-B-W coatings is also observed in as-deposited condition. The microhardness further improves on heat treatment. Tribological behavior of the heat treated coatings with varying load (10–50 N), sliding speed (0.25–0.42 m s−1) and operating temperature (25 °C–500 °C) were evaluated on a pin-on-disc type test setup while the wear mechanisms were also studied. Tribological behavior of Ni-B-W coatings is enhanced at 500 °C operating temperature in comparison with 100 or 300 °C due to formation of protective oxide scales and microstructural changes due to in-situ heat treatment effect.