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Lubricants, Volume 11, Issue 7 (July 2023) – 43 articles

Cover Story (view full-size image): One of the main challenges in maximizing vehicle performance is the prediction and optimization of tire behavior in different working conditions, such as temperature, friction, and wear. In the field of wear understanding, different approaches are under study both in academia and industry to comprehend and simplify the complexity of this phenomenon. Combining physical and data-driven analyses based on several statistical approaches and considering a large number of high-performance vehicle telemetries, track geometries, and road data samples, as well as tires’ viscoelastic properties, the proposed methodology represents an interesting insight towards the development of a simple and cost-effective tire wear model, which is able to take into account all of the most relevant phenomena. View this paper
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18 pages, 9873 KiB  
Article
Comparison of Different Standard Test Methods for Evaluating Greases for Rolling Bearings under Vibration Load or at Small Oscillation Angles
Lubricants 2023, 11(7), 311; https://doi.org/10.3390/lubricants11070311 - 24 Jul 2023
Cited by 1 | Viewed by 1262
Abstract
Rolling bearings operated at small oscillation angles or exposed to vibrations during standstill show typical damage after only a short period of operation. This can be false brinelling damage, so-called standstill marks or classic fretting damage (fretting corrosion, tribo-oxidation). It is important to [...] Read more.
Rolling bearings operated at small oscillation angles or exposed to vibrations during standstill show typical damage after only a short period of operation. This can be false brinelling damage, so-called standstill marks or classic fretting damage (fretting corrosion, tribo-oxidation). It is important to differentiate here according to the amplitude-ratio x/2b, which indicates the ratio between the rolling element Motion (x) and the Hertzian contact half-axis (b). Depending on this ratio, suitable laboratory test methods must be used to test the lubricating grease practically for the particular application. For this purpose, the Fafnir wear test, according to the standard of the American Society for Testing and Materials ASTM D4170, is also listed in the current high-performance multi-use specification of the National Lubricating Grease Institute (NLGI) as a release test for lubricating greases. In Europe, the SNR-FEB2 test is frequently used, which is also required to release greases in the blade bearings of wind turbines, among other things. In the case of standstill marks due to very small oscillation angles or vibrations, the Mannheim Tribology Competence Center (KTM) has developed a special test now established in the industry. The oscillating angles vary in these three different standard tests in the range from ±6° in the Fafnir test to ±3° in the SNR-FEB2 test to ±0.5° in the KTM standstill marking test; the x-to-2b ratios range from 5.5 (Fafnir) to 3.4 (SNR) to 0.5 (KTM). This paper will explain the scientific basis for these special operating and test conditions and compare test results of specially prepared model greases in these three standard rolling bearing tests, two test variations and a classical fretting test under oscillating sliding friction (ASTM D7594). The paper’s main objective is to show that the suitability of grease for such an application depends strongly on the prevailing operating conditions. Different tests in this field are, therefore, not interchangeable. Good results in one test do not automatically mean good results in a similar test at first glance. Therefore, selecting the right test for the application is important. Full article
(This article belongs to the Special Issue Tribological Studies of Roller Bearings)
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28 pages, 9061 KiB  
Article
Dynamics and Wear Prediction of Mechanisms Considering Multiple Clearances and Coatings
Lubricants 2023, 11(7), 310; https://doi.org/10.3390/lubricants11070310 - 22 Jul 2023
Viewed by 659
Abstract
The increase in joint clearance and system vibration caused by joint wear are important factors that may lead to the failure of the mechanism and a decrease in the motion accuracy of the actuator. In this paper, to investigate the impact of different [...] Read more.
The increase in joint clearance and system vibration caused by joint wear are important factors that may lead to the failure of the mechanism and a decrease in the motion accuracy of the actuator. In this paper, to investigate the impact of different numbers of spherical joint clearances on the dynamics performance of the mechanism and explore effective measures to reduce the vibration of the mechanism caused by multiple joint clearances, on the basis of the previous research on the mechanism dynamics when there is clearance in a single spherical joint, an improved contact force model is used to study the effects of coating, no coating, and different clearance quantities on the dynamics of a mechanism containing multiple spherical joint clearances. Moreover, the joint reaction forces and contact-impact forces under different working conditions are calculated. In order to reduce the difficulty of calculating the joint wear, an approximate calculation method for contact area is proposed, and an improved Archard wear model is employed to calculate and analyze the changes in wear amount under the influence of both spherical joint clearance and coating. Full article
(This article belongs to the Special Issue Advances in Wear Predictive Models)
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12 pages, 2624 KiB  
Article
A Study on the Corrosion Resistance of a Coating Prepared by Electrical Explosion of 321 Metal Wire
Lubricants 2023, 11(7), 309; https://doi.org/10.3390/lubricants11070309 - 22 Jul 2023
Viewed by 842
Abstract
Corrosion is known as a breakdown effect that causes the deterioration of substances in enriched petroleum/gas conditions. This reaction occurs in all materials, which is highlighted in alloys. In the present study, the morphological properties, as well as the corrosion resistance behavior of [...] Read more.
Corrosion is known as a breakdown effect that causes the deterioration of substances in enriched petroleum/gas conditions. This reaction occurs in all materials, which is highlighted in alloys. In the present study, the morphological properties, as well as the corrosion resistance behavior of the AISI1045 steel substrate coated with 321 austenitic stainless steel metal particulate fillers, were investigated. The electro-explosive spraying technique was employed to achieve a homogenous coating on the substrate surface. According to the results, the grain size of the 321 austenitic stainless steel coating layer was shrunk and reduced to 1–3 μm after the coating procedure. The coated layer also showed a homogenous and uniform thickness with an average value of 137 μm. Also, the average adhesion strength of 49.21 MPa was obtained between the sprayed coating and the substrate. The analytical analysis found the presence of Fe-Cr and Fe-Ni phases in the coating layer. The hardness of the original metal wire is 186 HV, and the microhardness of the coating after spraying is 232 HV. After subjecting the specimen to the corrosion examination, a 0.1961 mm/a corrosion rate was obtained for up to 120 h. Moreover, the corrosion products of CaCO3, Fe3O4, and MgFe2O4 were determined by XRD analysis. Furthermore, the observed results were further confirmed by the data obtained from EPMA and EDS evaluations. Hence, this study implies the beneficial role of electro-explosive sprayed alloy 321 austenitic stainless steel in creating a protective layer against corrosion on 45 steel substrate in an enriched oil/water environment. Full article
(This article belongs to the Special Issue Wear and Corrosion Behaviour of Metals and Alloys)
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22 pages, 9196 KiB  
Article
A New Thermal Elasto-Hydrodynamic Lubrication Solver Implementation in OpenFOAM
Lubricants 2023, 11(7), 308; https://doi.org/10.3390/lubricants11070308 - 22 Jul 2023
Viewed by 897
Abstract
Designing effective thermal management systems within transmission systems requires simulations to consider the contributions from phenomena such as hydrodynamic lubrication regions. Computational fluid dynamics (CFD) remains computationally expensive for practical cases of hydrodynamic lubrication while the thermo elasto-hydrodynamic lubrication (TEHL) theory has demonstrated [...] Read more.
Designing effective thermal management systems within transmission systems requires simulations to consider the contributions from phenomena such as hydrodynamic lubrication regions. Computational fluid dynamics (CFD) remains computationally expensive for practical cases of hydrodynamic lubrication while the thermo elasto-hydrodynamic lubrication (TEHL) theory has demonstrated good accuracy at a lower computational cost. To account for the effects of hydrodynamic lubrication in high-power transmission systems requires integrating TEHL into a CFD framework such that these methodologies can be interfaced. This study takes an initial step by developing a TEHL solver within OpenFOAM such that the program is prepared to be interfaced with a CFD module in future versions. The OpenFOAM solver includes the Elrod–Adams cavitation model, thermal effects, and elastic deformation of the surfaces, and considers mixing between the recirculating flow and oil feed by applying energy and mass continuity. A sensitivity study of the film mesh is presented to show the solution variation with refinement along the circumferential, axial and radial directions. A validation case is presented of an experimental single axial groove journal bearing which shows good agreement in the pressure and temperature results. The peak pressure in the film is predicted within 12% and the peak temperature in the bush is predicted within 5% when comparing the centerline profiles. Full article
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20 pages, 19159 KiB  
Article
Wear of Ni-Based Superalloy Tools in Friction Stir Processing of Commercially Pure Titanium
Lubricants 2023, 11(7), 307; https://doi.org/10.3390/lubricants11070307 - 21 Jul 2023
Cited by 1 | Viewed by 659
Abstract
Conventional methods for joining titanium alloys often provide a relatively low quality of joints impaired by high residual stresses. A possible solution to this problem can be offered by friction stir welding, which has been increasingly used for aluminum alloys. However, the friction [...] Read more.
Conventional methods for joining titanium alloys often provide a relatively low quality of joints impaired by high residual stresses. A possible solution to this problem can be offered by friction stir welding, which has been increasingly used for aluminum alloys. However, the friction stir welding of titanium alloys is complicated by severe tool wear due to high loads and temperatures in the process. Good results were reported for a tool made of ZhS6U superalloy, but tool life still needs to be improved. Here, we study the wear of a tool made of ZhS32 Ni-based superalloy, which has higher heat resistance than ZhS6U, and the wear of a liquid-cooled ZhS6U tool in the friction stir processing of commercially pure titanium. The effect of tool wear on the strength characteristics of the processed material is discussed. The total processing path length traversed by the tools without failure was 2790 mm. In both cases, the most severe wear was observed at the pin root. Liquid cooling significantly reduced the wear. Based on the obtained results, tool wear is proposed to occur by an adhesion–diffusion mechanism during friction stir processing. Full article
(This article belongs to the Special Issue Friction Stir Processing of Structural Metallic Materials)
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14 pages, 5529 KiB  
Article
Mechano-Chemical Properties and Tribological Performance of Thin Perfluoropolyether (PFPE) Lubricant Film under Environmental Contaminants
Lubricants 2023, 11(7), 306; https://doi.org/10.3390/lubricants11070306 - 21 Jul 2023
Viewed by 955
Abstract
Through molecular dynamics (MD) simulations with ReaxFF potential, the effects of chemical contaminants on the mechano-chemical properties and tribological performance of perfluoropolyether (PFPE) lubricants were investigated. For the two types of contaminants, i.e., silicon dioxide (SiO2) nanoparticles and water (H2 [...] Read more.
Through molecular dynamics (MD) simulations with ReaxFF potential, the effects of chemical contaminants on the mechano-chemical properties and tribological performance of perfluoropolyether (PFPE) lubricants were investigated. For the two types of contaminants, i.e., silicon dioxide (SiO2) nanoparticles and water (H2O), their molecular interactions with the two different PFPE lubricants, i.e., Ztetraol and ZTMD, were evaluated at the two different temperatures, i.e., 300 K and 700 K. Contaminants were adsorbed onto the PFPE lubricants at a controlled temperature. Then, air shear simulations were conducted to examine the mechano-chemical behaviors of the contaminated lubricants. Sliding contact simulations were performed to further investigate the tribological performance of the contaminated lubricants, from which the resulting friction and surface contamination were quantified. Lastly, chemical reactions between PFPE lubricants and contaminants were studied to investigate the degradation of PFPE lubricants. It was observed that SiO2 nanoparticles stiffened the PFPE lubricant, which decreased its shear displacement and increased friction. In the case of the H2O contaminant, it weakened and decreased the PFPE lubricant’s viscosity, increasing its shear displacement and lowering friction. However, the decreased viscosity by H2O contaminants can weaken the lubricity of the PFPE lubricant, leading to a higher chance of direct solid-to-solid contact under high contact force conditions. Full article
(This article belongs to the Special Issue Nanolubrication and Superlubrication)
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16 pages, 7826 KiB  
Article
Effect of a Metal Conditioner on the Physicochemical Properties and Tribological Performance of the Engine Oil SAE 5W-30 API SN
Lubricants 2023, 11(7), 305; https://doi.org/10.3390/lubricants11070305 - 21 Jul 2023
Viewed by 944
Abstract
Metal conditioners (MC) are added to lubricants to enhance their friction and wear in friction pairs, mainly in engines, gearboxes, and rolling bearings. Its growth in the Brazilian market is primarily focused on internal combustion engines. The effect of mixing MC with commercial [...] Read more.
Metal conditioners (MC) are added to lubricants to enhance their friction and wear in friction pairs, mainly in engines, gearboxes, and rolling bearings. Its growth in the Brazilian market is primarily focused on internal combustion engines. The effect of mixing MC with commercial engine oil (SAE 5W-30 API SN) was studied regarding the rheological and thermal properties. Also, the tribological performance of steel–steel contact was investigated. The rheological and thermal properties were determined by flow curves (at 20, 40, and 100 °C) and differential scanning calorimetry (DSC), respectively. Reciprocating fully-lubricated tests were performed at 40 °C and 80 °C (Po = 1.7 GPa, 5 Hz). Differences in the chemical composition between SAE 5W-30 and its mixture with MC were identified by infrared spectroscopy and related to their tribological performance. The coefficient of friction remained within the range of 0.09–0.1 for all conditions, typical of lubricated steel–steel contacts under boundary and mixed lubrication regimes. However, the mixture improved the wear resistance by around 33% when lubricated at 80 °C compared to the wear resistance offered by 5W-30. The formation of tribofilms with different chemical compositions was confirmed by SEM-EDS for all conditions. At both temperatures, the tribological performance reveals beneficial synergy between the metal conditioner and fully formulated oil additives. The tests lubricated with the mixture at 40 °C showed a less severe wear mechanism when compared to the tests lubricated with neat 5W-30. The study demonstrated that the mixture maintained the physicochemical properties of the commercial oil with a substantial anti-wear action at 80 °C. Full article
(This article belongs to the Special Issue Matching Ability and Anti-Wear Properties of Lubricants)
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21 pages, 6847 KiB  
Article
Individual Feature Selection of Rolling Bearing Impedance Signals for Early Failure Detection
Lubricants 2023, 11(7), 304; https://doi.org/10.3390/lubricants11070304 - 20 Jul 2023
Cited by 1 | Viewed by 922
Abstract
Condition monitoring of technical systems has increasing importance for the reduction of downtimes based on unplanned breakdowns. Rolling bearings are a central component of machines because they often support energy-transmitting elements like shafts and spur gears. Bearing damages lead to a high number [...] Read more.
Condition monitoring of technical systems has increasing importance for the reduction of downtimes based on unplanned breakdowns. Rolling bearings are a central component of machines because they often support energy-transmitting elements like shafts and spur gears. Bearing damages lead to a high number of machine breakdowns; thus, observing these has the potential to reduce unplanned downtimes. The observation of bearings is challenging since their behavior in operation cannot be investigated directly. A common solution for this task is the measurement of vibration or component temperature, which is able to show an already occurred bearing damage. Measuring the electrical bearing impedance in situ has the ability to gather information about bearing revolution speed and bearing loads. Additionally, measuring the impedance allows for the detection and localization of damages in the bearing, as early research has shown. In this paper, the impedance signal of five fatigue tests is investigated using individual feature selection. Additionally, the feature behavior is analyzed and explained. It is shown that the three different bearing operational time phases can be distinguished via the analysis of impedance signal features. Furthermore, some of the features show a significant change in behavior prior to the occurrence of initial damages before the vibration signals of the test rig vary from a normal state. Full article
(This article belongs to the Special Issue Recent Advances in Machine Learning in Tribology)
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19 pages, 5823 KiB  
Article
A Data-Driven Approach to Estimate the Power Loss and Thermal Behaviour of Cylindrical Gearboxes under Transient Operating Conditions
Lubricants 2023, 11(7), 303; https://doi.org/10.3390/lubricants11070303 - 20 Jul 2023
Viewed by 1195
Abstract
This paper proposes an innovative methodology to estimate the thermal behaviour of the cylindrical gearbox system, considering, as a thermal source, the power loss calculated under transient operating conditions. The power loss of the system in transient conditions is computed through several approaches: [...] Read more.
This paper proposes an innovative methodology to estimate the thermal behaviour of the cylindrical gearbox system, considering, as a thermal source, the power loss calculated under transient operating conditions. The power loss of the system in transient conditions is computed through several approaches: a partial elasto-hydrodynamic lubrication model (EHL) is adopted to estimate the friction coefficients of the gears, while analytical and semiempirical models are used to compute other power loss sources. Furthermore, considering a limited set of operating condition points as a training set, a reduced-order model for the evaluation of the power loss based on a neural network is developed. Using this method, it is possible to simulate thermal behaviour with high accuracy through a thermal network approach in all steady-state and transient operating conditions, reducing computational time. The results obtained by means of the proposed method have been compared and validated with the experimental results available in the literature. This methodology has been tested with the FZG rig test gearbox but can be extended to any transmission layout to predict the overall efficiency and component temperatures with a low computational burden. Full article
(This article belongs to the Special Issue Advances in Gear Tribology)
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26 pages, 10408 KiB  
Article
Impact of Temperature Variation on Friction Behaviour of Rare Earth-Doped Diamond-like Carbon Coatings with Ionic Liquid Lubricants
Lubricants 2023, 11(7), 302; https://doi.org/10.3390/lubricants11070302 - 20 Jul 2023
Cited by 3 | Viewed by 910
Abstract
This research paper investigates the tribological performance of diamond-like carbon (DLC) coatings doped with rare earth metals (europium and gadolinium) as well as pure DLC lubricated with ionic liquid additives (trihexyltetradecylphosphonium bis(2-ethylhexyl) phosphate {[P66614][DEHP]} and 1-ethyl-3-methylimidazolium diethyl phosphate {[EMIM][DEP]}) in Polyalphaolefin [...] Read more.
This research paper investigates the tribological performance of diamond-like carbon (DLC) coatings doped with rare earth metals (europium and gadolinium) as well as pure DLC lubricated with ionic liquid additives (trihexyltetradecylphosphonium bis(2-ethylhexyl) phosphate {[P66614][DEHP]} and 1-ethyl-3-methylimidazolium diethyl phosphate {[EMIM][DEP]}) in Polyalphaolefin 8 (PAO8). The study aims to examine the effect of temperature on the interaction between the coatings and additives by conducting tribological experiments using a block-on-disk setup at temperatures of 60 °C, 80 °C, and 100 °C. The primary objective is to evaluate the performance of doped DLC coatings compared to pure DLC coatings with ionic liquid additives in the lubricant in boundary lubrication conditions at various high working temperature environments. The experiments reveal that doped DLC coatings with ionic liquid additives exhibit superior tribological performance compared to pure DLC coatings. The rare earth metal dopants play a positive role in the formation of a tribofilm on the surface of the coatings as it interacts with ionic liquids, resulting in a lower coefficient of friction (CoF). Temperature influences the performance of the coatings and additives. The CoF increases with temperature for pure DLC coatings, while for doped DLC coatings it was significantly less. These findings highlight the influence of temperature on the tribological behavior of DLC coatings. Overall, this study contributes valuable insights into the impact of rare earth metal dopants and ionic liquid additives on the tribological performance of DLC coatings under different temperature conditions. The results demonstrate the potential of utilizing doped DLC coatings with ionic liquid additives as an effective approach to enhance the performance of mechanical systems. Full article
(This article belongs to the Special Issue Advances in Surface Engineering and Tribology)
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26 pages, 33723 KiB  
Article
The Influence of Phosphate-Ester-Based Additives on Metal Cutting Fluid Behavior during the Machining of Titanium Alloy
Lubricants 2023, 11(7), 301; https://doi.org/10.3390/lubricants11070301 - 19 Jul 2023
Viewed by 900
Abstract
The behavior of four phosphate ester additives with varying levels of phosphorus concentrations (very high, high, medium, and low) was examined through the course of drilling a Ti-6Al-4V titanium alloy at a constant metal removal rate (4.2 mm3/s). Cutting fluid (CF) [...] Read more.
The behavior of four phosphate ester additives with varying levels of phosphorus concentrations (very high, high, medium, and low) was examined through the course of drilling a Ti-6Al-4V titanium alloy at a constant metal removal rate (4.2 mm3/s). Cutting fluid (CF) additives were evaluated using torque, specific cutting energy (SEC), and tool wear. The drilling conditions employed had a significant influence on the performance of the phosphate ester additives. At 0.105 m/s and 0.188 m/s, the phosphate ester with very high phosphorous levels possessed the lowest SCE and torque values. The high-phosphorous-level phosphate ester displayed enhanced drilling performance at 0.293 m/s. At 0.419 m/s, the SCE and torque performance of the medium-phosphorous-level phosphate ester was preferable. The drilling performance of the phosphorus esters was observed to be related to the working mechanisms of the additives, which, in turn, was associated with the formation of a phosphorus-rich tribolayer and an organophosphate tribolayer on the cutting blade. Full article
(This article belongs to the Special Issue Methods of Application of Cutting Fluids in Machining)
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16 pages, 18254 KiB  
Article
Advanced Lubrication Simulations of an Entire Test Rig: Optimization of the Nozzle Orientation to Maximize the Lubrication Capability
Lubricants 2023, 11(7), 300; https://doi.org/10.3390/lubricants11070300 - 19 Jul 2023
Cited by 1 | Viewed by 938
Abstract
In the framework of the H2020 project IDERPLANE, aimed at providing innovative, effective, and validated criteria for the design and assessment of more reliable planet bearings for aerospace application analyzing the problem from a damage tolerance perspective, the present paper presents the numerical [...] Read more.
In the framework of the H2020 project IDERPLANE, aimed at providing innovative, effective, and validated criteria for the design and assessment of more reliable planet bearings for aerospace application analyzing the problem from a damage tolerance perspective, the present paper presents the numerical study and optimization of a test rig specifically designed for the experiments on the full-test article. Specifically, for the first time ever, an entire system including shafts, gears and bearings with all the rolling elements have been studied with a Finite Volume Computational Fluid Dynamics approach. This ambitious challenge was addressed with the implementation of a new mesh handling technique, namely the Global Remeshing Approach with Mesh Clustering (GRAMC). The aim was to optimize the lubrication of the test article to avoid unexpected failures during the experimental campaign. Three different oil jet directions have been studied and the most effective one, namely the axial one, was selected for the final test rig design. Full article
(This article belongs to the Special Issue Friction and Wear of Rolling-Element Bearings)
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16 pages, 3340 KiB  
Article
Research on the Rheological Characteristics of Wind Power Grease Based on Rheological Parameters
Lubricants 2023, 11(7), 299; https://doi.org/10.3390/lubricants11070299 - 19 Jul 2023
Cited by 1 | Viewed by 958
Abstract
Our research scrutinizes the impact of grease rheological properties on the lubrication performance of wind turbine spindle bearings. The rheological behavior of three distinct commercial wind turbine greases was examined with a rotational rheometer. Investigations into the viscoelastic, flow, and viscosity–temperature attributes of [...] Read more.
Our research scrutinizes the impact of grease rheological properties on the lubrication performance of wind turbine spindle bearings. The rheological behavior of three distinct commercial wind turbine greases was examined with a rotational rheometer. Investigations into the viscoelastic, flow, and viscosity–temperature attributes of the grease under varying temperatures were conducted, and the rheological parameters were fitted utilizing the Herschel–Bulkley (H–B) model. Constitutive equations of the grease derived from fitting the H–B model can efficaciously predict its rheological properties and viscosity–temperature behavior for wind power spindle bearings at disparate temperatures. Full article
(This article belongs to the Special Issue Grease II)
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14 pages, 4128 KiB  
Article
Research on H7006C Angular Contact Ball Bearing Slipping Behavior under Operating Conditions
Lubricants 2023, 11(7), 298; https://doi.org/10.3390/lubricants11070298 - 18 Jul 2023
Cited by 2 | Viewed by 1061
Abstract
During operation, angular contact ball bearings exhibit slipping behavior, which accelerates bearing wear and reduces the bearing’s overall service life. This paper focuses on studying the degree of slippage and the variation in slippage rate in the H7006C angular contact ball bearing under [...] Read more.
During operation, angular contact ball bearings exhibit slipping behavior, which accelerates bearing wear and reduces the bearing’s overall service life. This paper focuses on studying the degree of slippage and the variation in slippage rate in the H7006C angular contact ball bearing under constant inner ring speed and angular acceleration conditions. To achieve this objective, the study defines the contact between rolling elements, inner and outer rings, and the cage as flexible. A rigid–flexible coupling slippage dynamic simulation model is then developed, which utilizes cage slippage rate as the evaluation index. The analysis method of cage slippage rate change is established through the Gaussian function fitting method. By comparing simulation and testing results, the effectiveness of the analysis method of angular contact ball bearing slip behavior is validated. On this basis, the influence law of bearing speed and acceleration conditions on the slipping behavior of angular contact ball bearings is further studied. The results of the study show that as the axial load increases at different inner ring speeds, the cage speed increases until it reaches a stable state, while the cage slip rate continuously decreases until reaching a stable state. The higher the inner ring speed, the greater the axial load required for the bearing to enter the steady state. Under different angular accelerations, the cage speed increases with time; when the cage speed increases to stable and constant, the cage slip rate decreases to a stable state, and the higher the angular acceleration, the longer it takes for the bearing to enter the stable state. Full article
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14 pages, 5017 KiB  
Article
An Analysis of Edge Chipping in LiTaO3 Wafer Grinding Using a Scratch Test and FEA Simulation
Lubricants 2023, 11(7), 297; https://doi.org/10.3390/lubricants11070297 - 16 Jul 2023
Viewed by 945
Abstract
Lithium tantalite (LiTaO3) is a representative multifunctional single-crystal material with electro-optical, acoustic, piezoelectric, pyroelectric, and nonlinear optical properties used as a substrate for surface acoustic wave (SAW) devices. To enhance SAW device performance, thinner LiTaO3 substrates with improved surface roughness [...] Read more.
Lithium tantalite (LiTaO3) is a representative multifunctional single-crystal material with electro-optical, acoustic, piezoelectric, pyroelectric, and nonlinear optical properties used as a substrate for surface acoustic wave (SAW) devices. To enhance SAW device performance, thinner LiTaO3 substrates with improved surface roughness are desired. Chemical mechanical polishing (CMP) is employed to achieve the desired surface roughness after grinding. However, the thinning process increases the risk of substrate fracture, especially at the edges, resulting in edge chipping. Edge chipping can lead to complete substrate failure during SAW device fabrication, requiring an effective wafer geometry to prevent it. The study utilizes scratch tests and finite element analysis (FEA) to identify the optimal edge shape (C-cut, trimmed, and thinned) for preventing edge chipping on LiTaO3 wafers. The C-cut edge refers to the rounding of the wafer’s edge, while the trimmed edge refers to the machining of the wafer’s edge to be perpendicular to the wafer surface. As a result of the scratch tests, we observed edge-chipping lengths of 115 and 227 μm on the C-cut and trimmed edges, respectively, while the thinned edge (half C-cut) resulted in complete wafer fracture. In the finite element analysis (FEA), edge-chipping lengths of 80, 120, and 150 μm were obtained on the C-cut, trimmed, and thinned edges (half C-cut), respectively. In conclusion, it has been confirmed that the C-cut, trimmed, and thinned edge shapes are effective in preventing edge chipping. However, considering that the C-cut edge shape becomes thinner through grinding, using the trimmed edge shape appears to be the most effective. Full article
(This article belongs to the Special Issue Selected Papers from the K-TRIB2023)
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17 pages, 20306 KiB  
Article
Tribological and Micro-Mechanical Properties of Injected Polypropylene Modified by Electron Radiation
Lubricants 2023, 11(7), 296; https://doi.org/10.3390/lubricants11070296 - 15 Jul 2023
Viewed by 690
Abstract
Today, more and more importance is given to the improvement of polymer materials’ wear resistance, i.e., their micro-mechanical and tribological properties, which could widen their application in practice. The properties of materials can be modified by several methods, among them exposure to electron [...] Read more.
Today, more and more importance is given to the improvement of polymer materials’ wear resistance, i.e., their micro-mechanical and tribological properties, which could widen their application in practice. The properties of materials can be modified by several methods, among them exposure to electron radiation. This study focuses on the effect of varying radiation intensity (15 kGy to 99 kGy), depth of penetration, and subsequent structure modification of injection-molded polypropylene on tribological and micro-mechanical properties. Electron radiation influences the structure of individual layers, thus improving or degrading their properties. Hence, the depth of penetration can be examined by instrumented hardness tests and scratch tests. Due to irradiation, surface properties and wear resistance increased by up to 105% (from 38 MPa to 78 MPa). As the results show, an increase in mechanical properties was recorded in the direction towards the center of the sample (from 72 MPa to 82 MPa). Micro-mechanical tests were also confirmed by the observation of cross-linking changes (gel test) as well as crystallinity increases (wide-angle X-ray diffraction and microtome cuts). This finding could have a significant effect on the manufacturing and subsequent modification of injection-molded polypropylene parts, which opens new possibilities in practice for this material. The increased surface wear resistance enables the use of parts for which the durability and abrasion resistance of the surface are demanded, especially in applications facing exposure to long-term cyclical loads (e.g., gears). Full article
(This article belongs to the Special Issue Tribology of Polymer-Based Composites)
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19 pages, 3306 KiB  
Article
Experimental Study of the Rheology of Grease by the Example of CIATIM-221 and Identification of Its Behavior Model
Lubricants 2023, 11(7), 295; https://doi.org/10.3390/lubricants11070295 - 15 Jul 2023
Cited by 4 | Viewed by 1088
Abstract
The study of the rheological properties of a lubricant allows for the assessment of the structure’s durability in which they are used. Computer engineering enables the prediction of the structure performance using refined mathematical models of its materials. This paper presents an experimental [...] Read more.
The study of the rheological properties of a lubricant allows for the assessment of the structure’s durability in which they are used. Computer engineering enables the prediction of the structure performance using refined mathematical models of its materials. This paper presents an experimental investigation of the rheological behavior of a lubricant that is actively used in bridge structures. The paper proposed a methodology for determining the rheological characteristics of the lubricant using a rotational viscometer. Additionally, the article performed the task of identifying the mathematical model of the lubricant behavior based on the Maxwell body, using two approaches: the Anand model and the Prony series. The proposed models allow for numerical modeling of the structure’s performance throughout their lifecycle within the scope of computer engineering. Full article
(This article belongs to the Special Issue Advances in Bearing Lubrication and Thermodynamics 2023)
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14 pages, 2974 KiB  
Article
Calculation of Dynamic Coefficients of Air Foil Journal Bearings Using Time-Domain Identification
Lubricants 2023, 11(7), 294; https://doi.org/10.3390/lubricants11070294 - 13 Jul 2023
Viewed by 1136
Abstract
Dynamic coefficients of a bearing are basic elements of rotor dynamics analysis. At present, there are still some issues in the calculation of the dynamic coefficient of air foil bearing. In this paper, the dynamic coefficients of the air foil bearing are calculated [...] Read more.
Dynamic coefficients of a bearing are basic elements of rotor dynamics analysis. At present, there are still some issues in the calculation of the dynamic coefficient of air foil bearing. In this paper, the dynamic coefficients of the air foil bearing are calculated by time-domain identification. This method does not need to linearize the system equations, so it is generally applicable to different models for air foil bearings. Using the established method, this paper verified the calculation results using the foil model with axial uniform deformation for the first time, and the influence of the foil model on the dynamic coefficients was studied. The calculation results of the foil models with axial uniform deformation and axial independent deformation have significant differences. Furthermore, the accuracy of the dynamic coefficient method for different disturbance amplitudes was compared. The results indicate that the dynamic coefficient method has good accuracy over a large disturbance range. Full article
(This article belongs to the Special Issue Condition Monitoring and Simulation Analysis of Bearings)
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14 pages, 4948 KiB  
Article
Effects of Hyperelliptic Bearings Bush on Connecting Rod Big-End Lubrication and Design Optimization
Lubricants 2023, 11(7), 293; https://doi.org/10.3390/lubricants11070293 - 12 Jul 2023
Cited by 1 | Viewed by 819
Abstract
Aiming at the impact of bearing bushes on the lubrication and friction and wear of diesel engine connecting rod big-end bearings, a certain type of diesel engine connecting rod big-end bearing bush was taken as the research object and a multi-body dynamics numerical [...] Read more.
Aiming at the impact of bearing bushes on the lubrication and friction and wear of diesel engine connecting rod big-end bearings, a certain type of diesel engine connecting rod big-end bearing bush was taken as the research object and a multi-body dynamics numerical calculation model of the connecting rod group was built. The connecting rod big-end bearing bushes with four profiles: exponential, hyperelliptic, barrel and trapezoid were used to study the effect on bearing lubrication. The study found that the hyperelliptic bush has the best lubrication performance for the connecting rod big-end bearing. On the basis of the hyperelliptic bush, the bearing clearance, bearing width, journal oil hole diameter and oil supply pressure are used as design variables, using the Box–Behnken experimental design and radial basis function (RBF) neural network method to construct an approximate multi-objective model, which the minimum oil film thickness (abbreviated as MOFT) and average rough contact effective pressure are the objectives. A non-dominated sorting genetic algorithm (NSGA-II) is used for multi-objective optimization. The optimization results show that the bearing clearance remains basically unchanged, the bearing width, journal oil hole diameter and oil supply pressure increase, so that MOFT of the connecting rod big-end bearing rises from 1.56 μm to 1.97 μm, and the average rough contact effective pressure increases from 3.97 MPa decreases to 0.25 MPa. The research results can provide a reference for the analysis and optimization of the lubrication performance of the connecting rod big-end bearing. Full article
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18 pages, 8534 KiB  
Review
Current Knowledge on Friction, Lubrication, and Wear of Ethanol-Fuelled Engines—A Review
Lubricants 2023, 11(7), 292; https://doi.org/10.3390/lubricants11070292 - 12 Jul 2023
Cited by 2 | Viewed by 1555
Abstract
The urgent need for drastic reduction in emissions due to global warming demands a radical energy transition in transportation. The role of biofuels is fundamental to bridging the current situation towards a clean and sustainable future. In passenger cars, the use of ethanol [...] Read more.
The urgent need for drastic reduction in emissions due to global warming demands a radical energy transition in transportation. The role of biofuels is fundamental to bridging the current situation towards a clean and sustainable future. In passenger cars, the use of ethanol fuel reduces gas emissions (CO2 and other harmful gases), but can bring tribological challenges to the engine. This review addresses the current state-of-the-art on the effects of ethanol fuel on friction, lubrication, and wear in car engines, and identifies knowledge gaps and trends in lubricants for ethanol-fuelled engines. This review shows that ethanol affects friction and wear in many ways, for example, by reducing lubricant viscosity, which on the one hand can reduce shear losses under full film lubrication, but on the other can increase asperity contact under mixed lubrication. Therefore, ethanol can either reduce or increase engine friction depending on the driving conditions, engine temperature, amount of diluted ethanol in the lubricant, lubricant type, etc. Ethanol increases corrosion and affects tribocorrosion, with significant effects on engine wear. Moreover, ethanol strongly interacts with the lubricant’s additives, affecting friction and wear under boundary lubrication conditions. Regarding the anti-wear additive ZDDP, ethanol leads to thinner tribofilms with modified chemical structure, in particular shorter phosphates and increased amount of iron sulphides and oxides, thereby reducing their anti-wear protection. Tribofilms formed from Mo-DTC friction modifier are affected as well, compromising the formation of low-friction MoS2 tribofilms; however, ethanol is beneficial for the tribological behaviour of organic friction modifiers. Although the oil industry has implemented small changes in oil formulation to ensure the proper operation of ethanol-fuelled engines, there is a lack of research aiming to optimize lubricant formulation to maximize ethanol-fuelled engine performance. The findings of this review should shed light towards improved oil formulation as well as on the selection of materials and surface engineering techniques to mitigate the most pressing problems. Full article
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15 pages, 4032 KiB  
Article
Wear Performance of Cu–Cd, Cu–Be and Cu–Cr–Zr Spot Welding Electrode Materials
Lubricants 2023, 11(7), 291; https://doi.org/10.3390/lubricants11070291 - 11 Jul 2023
Cited by 1 | Viewed by 1038
Abstract
Heating of the electrode at the work–piece interface zone in spot welding, leading to degradation of the tip, becomes a significant concern in the high-volume production automotive industry. By recognizing the interrelationship between hardness, wear resistance, and thermal conductivity, the authors emphasize the [...] Read more.
Heating of the electrode at the work–piece interface zone in spot welding, leading to degradation of the tip, becomes a significant concern in the high-volume production automotive industry. By recognizing the interrelationship between hardness, wear resistance, and thermal conductivity, the authors emphasize the importance of selecting electrode materials with suitable alloying elements desirable for achieving optimal performance in spot welding applications. This paper studies the wear behaviour of three types of spot-welding electrode materials under dry sliding contact conditions. A pin-on-disc tester was used to investigate Cu–Cd, Cu–Be and Cu–Cr–Zr alloys’ wear behaviour under variable parametric load, temperature and time conditions. Taguchi L9 orthogonal array was used to investigate the significance of parameters and their effect on linear wear. The ranking of the parameters was performed using SN ratio analysis. The wear mechanism was also studied using SEM analysis. Abrasive wear was observed at lower loads, while adhesion, oxidation and plastic deformation were observed under high-load and -temperature conditions. This study suggests an alternative to the presently used electrolytic tough pitch (ETP) Cu electrode involving equally good wear-resistance material. However, a detailed investigation on the effect of plasma on the metallurgical characteristics of selected material is suggested. Full article
(This article belongs to the Special Issue Advances in Surface Engineering and Tribology)
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15 pages, 10600 KiB  
Article
The Effect of Nanoparticle Additives on the Lubricity of Diesel and Biodiesel Fuels
Lubricants 2023, 11(7), 290; https://doi.org/10.3390/lubricants11070290 - 11 Jul 2023
Viewed by 877
Abstract
Fuel lubricity is an essential property that ensures the longevity end efficiency of diesel CI engines. Nanomaterials have been shown to have the potential to improve lubricity in many different lubricating substances, including fuels. Moreover, the combustion process has also been shown to [...] Read more.
Fuel lubricity is an essential property that ensures the longevity end efficiency of diesel CI engines. Nanomaterials have been shown to have the potential to improve lubricity in many different lubricating substances, including fuels. Moreover, the combustion process has also been shown to improve with the introduction of nanomaterials. This study investigated a series of nanoparticles, including carbon nanoplates, carbon nanotubes, aluminum oxide, zinc oxide, and cerium oxide, as lubricity-enhancing additives for selected fuels. Conventional diesel fuel and rapeseed oil methyl ester, referred to as biodiesel, were chosen as base fuels for modification. The lubricity was evaluated according to the standard test method ASTM 6079 using the HFRR tribometer. The leading lubricity indicators were the wear scar diameter, wear volume, and coefficient of friction. In addition, the worn surface analysis was performed to elucidate the lubrication mechanism. The results show that the addition of nanoparticles can improve the lubricity of both investigated fuels. However, the effect differed among nanoparticles and fuels. In summary, carbon nanotubes could be a rational choice for both fuels. In addition, zinc oxide improved the lubricity of diesel fuel, while carbon nanoplatelets and aluminum oxide nanoparticles showed improvements in the lubricity of biodiesel. Full article
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27 pages, 2752 KiB  
Review
Recent Progress of Machine Learning Algorithms for the Oil and Lubricant Industry
Lubricants 2023, 11(7), 289; https://doi.org/10.3390/lubricants11070289 - 10 Jul 2023
Cited by 2 | Viewed by 1738
Abstract
Machine learning (ML) algorithms have brought about a revolution in many industries where otherwise operation time, cost, and safety would have been compromised. Likewise, in lubrication research, ML has been utilized on many occasions. This review provides an in-depth understanding of seven ML [...] Read more.
Machine learning (ML) algorithms have brought about a revolution in many industries where otherwise operation time, cost, and safety would have been compromised. Likewise, in lubrication research, ML has been utilized on many occasions. This review provides an in-depth understanding of seven ML algorithms from a tribological perspective. More specifically, it presents a comprehensive overview of recent advancements in ML applied to lubrication research, organized into four distinct categories. The first category, experimental parameter prediction, highlights the significant contributions of artificial neural networks (ANNs) in accurately forecasting operating conditions related to friction and wear. These predictions offer valuable insights that aid in forensic preparation. Discriminant analysis, Bayesian modeling, and transfer learning approaches have also been used to predict experimental parameters. Second, to predict the lubrication film thickness and identify the lubrication regime, algorithms such as logistic regression and ANN were useful. Such predictions provide up to 99.25% accuracy. Third, to predict the friction and wear for a given experimental condition, support vector machine (SVM), polynomial regression, and ANN offered an accuracy above 93%. Finally, for condition monitoring for bearings, gearboxes, gear trains, and similar critical situations where regular in-person inspection is difficult, Naïve Bayes, SVM, decision trees, and ANN were utilized to predict the safe life of lubricants. This review highlighted these four aspects with state-of-the-art examples and discussed the current situation and projected future possibilities of lubricant design facilitated by ML techniques. Full article
(This article belongs to the Special Issue Tribology and Machine Learning: New Perspectives and Challenges)
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16 pages, 6062 KiB  
Article
Friction and Wear in Stages of Galling for Sheet Metal Forming Applications
Lubricants 2023, 11(7), 288; https://doi.org/10.3390/lubricants11070288 - 07 Jul 2023
Cited by 1 | Viewed by 983
Abstract
Aluminum is a very commonly used material at present, and roughly half of the produced aluminum products undergo forming during manufacturing. Galling is a severe form of wear that occurs during sheet metal forming operations and is a common failure mode of materials [...] Read more.
Aluminum is a very commonly used material at present, and roughly half of the produced aluminum products undergo forming during manufacturing. Galling is a severe form of wear that occurs during sheet metal forming operations and is a common failure mode of materials in sliding contact; however, the causes and mechanisms of galling are poorly understood. In this work, sliding wear experiments were conducted to produce galling wear between a tool steel ball bearing and aluminum alloy Al5083, to study the relationship between the coefficient of friction, the lump growth on the tool and the scratch morphology. Whilst the characteristic friction regimes were observed, the characteristic damage (grooves running parallel to the scratch direction) was not observed. Instead, when galling was developed on the indenter, the scratch surface morphology displayed a series of peaks and grooves perpendicular to the scratch direction. It is likely that the difference in scratch morphology observed once galling was initiated is due to the lower hardness and reduced work hardening behavior of the Al5083 alloy, compared to the high strength steels previously examined in sheet metal forming applications. The evolution of the scratch morphology has been characterized in a novel way by investigating the distribution of the longitudinal cross-section profile height along the scratch length in relation to the three-stage friction regime observed. This showed that, as the galling wear progressed, the longitudinal cross-section profile height distribution shifts towards negative values, with a corresponding shift in the distribution of material transferred to the tool shifting to the positive. This indicates that, as the amount of material adhered to the indenter increased, the depth of the grooves on the scratch surface perpendicular to the sliding direction also increased. Full article
(This article belongs to the Special Issue Wear Behavior of Aluminum Matrix Composite)
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15 pages, 5211 KiB  
Article
Photoluminescence Induced in Mineral Oil by Ionizing Radiation
Lubricants 2023, 11(7), 287; https://doi.org/10.3390/lubricants11070287 - 07 Jul 2023
Viewed by 1061
Abstract
We have studied photoluminescence (PL) properties of vacuum pump mineral oil as a function of the type and intensity of ionizing radiation exposure. The mineral oil has a simple aliphatic structure, which possesses no chromophore in the traditional sense. Unexpected PL in the [...] Read more.
We have studied photoluminescence (PL) properties of vacuum pump mineral oil as a function of the type and intensity of ionizing radiation exposure. The mineral oil has a simple aliphatic structure, which possesses no chromophore in the traditional sense. Unexpected PL in the mineral oil has characteristic features such as variation of the emission peak wavelength depending on the excitation wavelength and intensity dramatically increasing with radiation dose. The observed behavior can be understood in the framework of a previously suggested model introducing aggregation-induced PL and the formation of conjugated clusters comprising nontraditional chromophores. Our findings can be used for the development of optical sensors for real-time monitoring of oil utilized in vacuum pumps in nuclear fusion reactors. Full article
(This article belongs to the Special Issue Radiation Tolerant Lubricants)
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13 pages, 10949 KiB  
Article
Influence of Research Factors and Al2O3 Layer Production Parameters on Tribological and Microstructural Properties
Lubricants 2023, 11(7), 286; https://doi.org/10.3390/lubricants11070286 - 06 Jul 2023
Viewed by 900
Abstract
The exclusion of systems supplying the lubricant from the outside makes it necessary to replace traditional sliding pairs with materials containing a lubricant component. Such solutions are carried out to prevent the formation of material tacks and, consequently, of adhesive wear, which must [...] Read more.
The exclusion of systems supplying the lubricant from the outside makes it necessary to replace traditional sliding pairs with materials containing a lubricant component. Such solutions are carried out to prevent the formation of material tacks and, consequently, of adhesive wear, which must be avoided. The article presents the influence of research factors and parameters of Al2O3 layer production on tribological and microstructural properties. The input variables for the tests were the admixture of WS2 to the electrolyte, the type of sputtering of the samples for SEM tests, and the load on the oxide coating—TG15 material friction node. The surface morphology and cross-section of the oxide coatings as well as the tribological properties of the rubbing pair have been studied. Interactions between the input variables and the obtained test results have been analyzed using DOE—a 2k factorial design with one repetition. Pareto charts and two-way ANOVA were used to determine the relationship. The analysis of variance shows the influence of sample preparation on the calculation values of the size of nanopores and Al2O3 walls on the SEM image. Statistical analyzes also show that both the load and the type of electrolyte affected the values of the coefficient of friction and wear of the TG15 material; those values are the result of appropriate adhesion of the sliding film to the surface of the layer. Full article
(This article belongs to the Special Issue Assessment of Adhesive Wear)
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17 pages, 52292 KiB  
Article
Influence of Tempering Temperature on Abrasive-Wear Performance of High-Chromium-Based Multicomponent White Cast Iron
Lubricants 2023, 11(7), 285; https://doi.org/10.3390/lubricants11070285 - 05 Jul 2023
Viewed by 1022
Abstract
Recently, high-Cr multicomponent white cast iron after quenching is known to have superior abrasive-wear resistance. However, this material is prone to cracking due to the precipitation of very hard carbides resulting in very limited application. However, the cracking tendency might be reduced by [...] Read more.
Recently, high-Cr multicomponent white cast iron after quenching is known to have superior abrasive-wear resistance. However, this material is prone to cracking due to the precipitation of very hard carbides resulting in very limited application. However, the cracking tendency might be reduced by appropriate tempering temperature. Therefore, the three-body abrasive-wear resistance of 18 wt.% and 27 wt.% Cr based on 3 wt.% Mo, W, V, and Co with different temperatures of tempering was studied. These are abbreviated as 18Cr MCCI and 27Cr MCCI. The tempering temperature range was 653–813 K with an interval of 20 K after the quenching process. The quenched specimens were used as comparison materials, and three tempered specimens were selected. Thus, there are quenched (Q), quenched-tempered at low temperature (TLT), quenched-tempered at medium temperature (TMT), and quenched-tempered at high temperature (THT) specimens. From the results, it can be known that the wear resistance of the material decreases as Cr percentage and tempering temperature increase. Therefore, the 18Cr MCCI Q has better wear performance than specimens of other conditions. Yet, different results occur in the group of 27Cr MCCI. The material is more wear-resistant after tempering despite the lower hardness of the material. This might be owing to the higher fracture toughness of the M7C3 carbide, which is higher after the tempering process compared with quenching only. Therefore, it can be said that it is important to maintain the hardness of the material to achieve better wear resistance. However, in materials containing large M7C3 carbides, the fracture toughness of carbides should also be considered. Full article
(This article belongs to the Special Issue Frictional Behavior and Wear Performance of Cast Irons)
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48 pages, 15715 KiB  
Review
Fundamental Structure–Function Relationships in Vegetable Oil-Based Lubricants: A Critical Review
Lubricants 2023, 11(7), 284; https://doi.org/10.3390/lubricants11070284 - 04 Jul 2023
Cited by 2 | Viewed by 1957
Abstract
Vegetable oil (VO)-based lubricants are environmentally friendly replacements for mineral oils. This work critically reviews the literature and identifies the molecular structures in VO-based lubricants which have been used to improve performance. The specific roles that size, type, number, position, spatial arrangement, and [...] Read more.
Vegetable oil (VO)-based lubricants are environmentally friendly replacements for mineral oils. This work critically reviews the literature and identifies the molecular structures in VO-based lubricants which have been used to improve performance. The specific roles that size, type, number, position, spatial arrangement, and symmetry play in determining lubricating functionality were highlighted. Data were systematically collected to identify the contributions of major structural components and relate them to specific physical functionality measurables. The relationships were presented to reveal structure–function trends. Empirical predictive relationships between flow and thermal transition properties and structures were established. Molecular mass was revealed to be a fundamental determinant of viscosity and transition temperatures, but these properties were shown to also be influenced by other structural factors such as polar functional groups, branching, and symmetry. Almost all the examined viscosity data plotted versus molecular mass are enclosed within the 95% prediction band of an exponential rise to a maximum function (R2 = 0.7897). Generally, for both flow and thermal transition, a given structure versus function follows simple linear or exponential functions with unbranched VO-based lubricants, lending themselves more easily to strong correlations. This review is a first step towards comprehensively relating structure to lubrication function. The revealed relationships of structural contributions to the lubricating functionality of VO-based lubricants provide insights that may be used to extend the ranges of chemical and physical properties of some molecular architectures examined. Full article
(This article belongs to the Special Issue Advances in Biolubrication and Biomaterials)
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14 pages, 5432 KiB  
Article
Investigation of the Hardness Development of Molybdenum Coatings under Thermal and Tribological Loading
Lubricants 2023, 11(7), 283; https://doi.org/10.3390/lubricants11070283 - 30 Jun 2023
Viewed by 777
Abstract
The increasing global demand for innovative and environmentally friendly lubricants can be met through the use of solid lubricants. By switching from conventional lubricants such as various oils or grease to solid lubricants, new scopes of application can also be opened up. The [...] Read more.
The increasing global demand for innovative and environmentally friendly lubricants can be met through the use of solid lubricants. By switching from conventional lubricants such as various oils or grease to solid lubricants, new scopes of application can also be opened up. The main requirements for solid lubricants are a reduction in the coefficient of friction (CoF) and an increase in wear resistance. Due to the favourable material properties, molybdenum (Mo) coatings fulfil the tribological requirements and are therefore promising solid lubricants which can be applied via physical vapour deposition (PVD). In this work, the impact of substrate temperature on the hot hardness of deposited Mo coatings was determined. The specimen with the highest hot hardness was then tribologically examined both at the micro and nano level. Through an analysis of the wear tracks by means of nanoindentation and scanning electron microscopy (SEM), it was possible to detect the influence of the tribological load separately from that of the thermal loads. The results showed that the tribological load influenced the Mo coating by significantly increasing its hardness. This was achieved due to the work hardening of the Mo layer leading to an increase in the wear resistance of the coating. Full article
(This article belongs to the Special Issue Multiscale Tribology of Solid Lubricants)
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11 pages, 3583 KiB  
Article
Corrosion Behavior and Comprehensive Evaluation of Al0.8CrFeCoNiCu0.5B0.1 High-Entropy Alloy in 3.5% NaCl Solution
Lubricants 2023, 11(7), 282; https://doi.org/10.3390/lubricants11070282 - 30 Jun 2023
Cited by 1 | Viewed by 1105
Abstract
In this study, Al0.8CrFeCoNiCu0.5B0.1 high-entropy alloy coating was prepared on the surface of 5083 aluminum alloy using laser cladding technology. The corrosion behavior of the coating and substrate in 3.5% NaCl solution was analyzed using experimental methods, including [...] Read more.
In this study, Al0.8CrFeCoNiCu0.5B0.1 high-entropy alloy coating was prepared on the surface of 5083 aluminum alloy using laser cladding technology. The corrosion behavior of the coating and substrate in 3.5% NaCl solution was analyzed using experimental methods, including polarization curves and electrochemical impedance spectroscopy. The corrosion current density of Al0.8CrFeCoNiCu0.5B0.1 coating is 2.04 × 10−7 A/cm 2. The passivation range width reaches 2.771 V, and these polarization test results are superior to the substrate. The Al0.8CrFeCoNiCu0.5B0.1 coating exhibited selective corrosion behavior, with the Cu-rich FCC1 phase and Cr-poor phase being susceptible to corrosion, leading to localized pitting and intergranular corrosion traces, but the corrosion did not spread extensively. The intergranular distribution of Cu is the main reason for the intergranular corrosion trace features. In contrast, the substrate exhibited overall corrosion. The Nyquist plot of the Al0.8CrFeCoNiCu0.5B0.1 coating consisted of a single capacitive semicircle arc in the high-frequency region with a larger radius than the substrate. In conclusion, using the Al0.8CrFeCoNiCu0.5B0.1 high-entropy alloy as a coating can significantly improve the corrosion resistance of the 5083 aluminum alloy substrate. Full article
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