This study examines the wear characteristics of case-carburized steel surfaces with manganese phosphate (MnPh) coating under commercial fully formulated oil (FFO). This combination can improve the steel’s tribological properties and rolling contact fatigue strength. The role of oil additives in FFO, which affect the wear characteristics through the formation of a wear-resistant tribofilm, on the MnPh coated steel was analyzed in detail. The process of chemical etching during the MnPh coating application makes the steel substrate rougher. Consequently, both MnPh-coated and MnPh-removed disks were analyzed to ensure comparability in terms of surface roughness and morphology. Under FFO lubrication, the MnPh-coated disks exhibited continuous wear of the steel peaks during the initial friction period, similar to that observed under base oil lubrication. This continuous wear occurs because the residual MnPh coating in the valleys of the roughness primarily supports the contact load during the initial friction period, preventing the formation of a wear-resistant tribofilm on the exposed steel peaks. The proposed wear mechanism for MnPh-coated steel aims to further improve the rolling contact fatigue strength.

This study explores the remarkable potential of garlic oil as a green, high-performance lubricant in machining, aiming to elevate wear resistance, reduce cutting temperatures, and improve surface finishes, all in contrast to conventional dry cutting methods. Through Scanning Electron Microscopy (SEM), intricate wear patterns on tungsten carbide (WC) tool inserts were meticulously analyzed, while Energy Dispersive X-ray Spectroscopy (EDS) unveiled the adhesive behavior influenced by the garlic oil-based lubrication. Surface roughness, following the turning operation, was elegantly measured using stylus profilometry. The results reveal that garlic oil-based Minimum Quantity Lubrication (MQL) achieved a 43.8% reduction in flank wear, a 69.3% decrease in cutting temperatures, and an impressive 79.3% improvement in surface finish. These findings illuminate garlic oil’s ability to maintain cooler cutting zones, significantly extending tool life while preserving the precision of machined parts. This research underscores the promise of garlic oil as a natural, eco-friendly lubricant, paving the way for sustainable machining practices that not only protect the environment but also ensure unparalleled performance in the processing of EN24 steel.

Pendulum friction-tester is specifically useful for experiments in biotribological field because that is good at the measure on circular sliding surfaces, like as synovial joints, joint prostheses, eye balls, or contact lenses. Stanton’s formula has been generally used for the data processing as the calculation of friction coefficient from the amplitude decay during a pendulum libration. Because Stanton used the balance of moment to analyze the pendulum motion, his analysis must inevitably include an approximation of sin θ as angle θ. However, the error in the formula has not been evaluated because the strict analysis was thought to be impossible. In the present study, the strict analysis was clarified by energy balance in a pendulum. As the result, error in Stanton’s formula was able to be evaluated.

Carbon-based nanomaterials have been employed as lubricants in industrial settings due to their low-friction properties. Among them, graphene oxide (GO) has been employed in a variety of applications because it is more hydrophilic than graphene and disperses easily in polar solvents. Furthermore, it has low production costs and low environmental impact. These properties render it a promising new lubricant additive with the potential to supplant long-used organometallic lubricant additives. It has been reported that GO exhibits low friction not only in water lubrication, but also in oil lubrication with GO-modified alkyl groups. In this study, a hierarchical GO model was constructed by molecular dynamics simulations using the reactive force field (ReaxFF) and compared with friction experiments. The analysis revealed that GO is stable in water but sensitive to pressure in oil. Sheets in contact with oil showed instability, moving from side to side. Furthermore, the alkyl-modified GO appeared to be integrated with the oil, suggesting that the alkyl groups contribute to the observed low-friction properties. These results are in qualitative agreement with the experimental data and indicate that the behavior of GO is solvent dependent.

A contact between surfaces with low roughness (approximately 0.01–0.1 μm) and relatively large nominal contact area (mm² order) is a complex phenomenon that requires consideration of deformation behavior at various scales, and is an important subject in contact mechanics. Contact simulation using the elastoplastic boundary element method is considered to be effective for this analysis. However, only a few studies have examined such contacts with a detailed comparison to measurement data, meaning that the simulation accuracy has not been sufficiently verified. Therefore, in this study, to verify their accuracy, simulations for low roughness and large area contact were performed using actual roughness shape data, and were compared with optical interferometry data of the contact surface shapes obtained in a previous study. The calculated distribution of the gap between two surfaces was similar to the measured data. Furthermore, nominal contact areas were determined from each distribution based on the statistical theory. The simulation results for nominal contact area sizes and average gaps were in good agreement with experimental results. Our findings demonstrate the utility of the elastoplastic boundary element method for the multi-scale contact analysis of surfaces with low roughness and large nominal contact area.

The investigation examined the characteristics and utilization of TiCN coatings on high-speed steel substrates. These coatings were produced via unfiltered cathodic arc physical vapor deposition, commencing with a TiN layer and culminating in a TiCN layer with diverse carbon concentrations. The study found that the coatings exhibited a consistent composition of TiC_0.7N_0.3 and a fine-grained microstructure with an average thickness of approximately 3.4 µm. Nanoindentation tests revealed a high average hardness of 30.74 GPa and Young’s modulus of 349.95 GPa. The coatings’ friction and wear behavior showed temperature dependence, with increased oxidation and phase transformation at elevated temperatures, while consistent performance was observed at room temperature. The TiCN coatings demonstrated excellent mechanical properties and temperature-dependent wear resistance, indicating their suitability for industrial applications requiring high hardness and thermal stability. This study provides valuable insights for optimizing deposition parameters to enhance the coating’s performance in challenging environments. Scratch tests confirmed the coatings’ strong adhesion, with cohesion failing at 49.1 N and adhesion failing at 70.2 N.

In the rolling bearings used in automotive electrical instruments and auxiliary devices such as alternators, it is well-known that brittle flaking occurs earlier than expected due to hydrogen embrittlement. Despite this, in the flaking mechanism, the generation process of hydrogen atoms in lubricating oils has not been clarified microscopically. In this study, we theoretically elucidated the reaction processes of poly-α-olefin (PAO) and alkyl diphenyl ether (ADE) molecules using quantum mechanical (QM) calculations. The basic and important mechanism for the generation of hydrogen molecules was clarified for the first time at the atomic level. Upon considering the generation mechanism on ceramics and nascent steel surfaces, it was found that the reason why the amount of hydrogen generation is similar regardless of the type of lubricant is because the energy required for hydrogen generation is almost the same. Furthermore, it was suggested that the suppression of hydrogen brittle flaking by ADE was due to the low exposure frequency of the nascent steel surface.

This study investigated the dry sliding wear behavior of Cor-Ten steel, a material commonly used in harsh environments such as ports, sea bridges, and drilling rigs. Understanding how Cor-Ten steel performs in abrasive conditions is crucial for predicting potential wear issues. To assess its wear performance, tests were conducted using three types of abrasive balls: AISI-52100 steel, WC-Co, and Alumina. The wear tests involved a reciprocating ball-on-disc device at loads of 3, 7, and 10 N and sliding speeds of 0.4 mm/s and 0.8 mm/s. Results showed that the largest wear volumes occurred with the Alumina ball, while the AISI 52100 steel ball, despite its lower hardness, produced higher wear volumes than the WC-Co ball. Additionally, increased sliding speed led to higher wear volumes across all tests. SEM images revealed distinct wear tracks on both surfaces. These results provide valuable insights into the wear mechanisms of Cor-Ten steel, which can aid in optimizing material selection and maintenance strategies in marine construction.

An Electro-rheological (ER) fluid comprises dielectric particles blended in a non-conducting oil. The ER lubricants are commonly known as smart lubricants. This study utilizes an ER lubricant to examine the static and dynamic response of multi-lobe journal bearing. The lubricant flow within the journal-bearing clearance space is described by Reynold’s equation, while the non-linear behavior of the lubricant is characterized using the Bingham model. The solution of the Reynolds equation is obtained employing the Newton-Raphson method, with numerical addressing of gaseous cavitation in the fluid film through a mass-conserving algorithm. The effects of lobe geometry and the applied electric field are scrutinized on bearing performance metrics. The equation of motion for the journal is solved utilizing the fourth-order Runge-Kutta method to predict journal center locus/trajectories. The utilization of ER lubricant in conjunction with a two-lobe journal bearing notably enhances the minimum film thickness by 63.5%, the direct stiffness parameter by 182.4%, and the damping parameter by 210.14%. The multi-lobe configuration adversely affects the frictional power loss of the bearing system. The threshold speed, a critical parameter in the design and operation of journal bearings, is improved by the ER effect and is higher for multi-lobe bearings. In multi-lobe configurations of journal bearings operating with ER lubricant, linear motion journal trajectories are noted to be smaller and more stable. Under given operating conditions, designers should prioritize two-lobe journal bearings operating with ER lubricants, as they exhibit greater stability and superior performance metrics in both steady-state and dynamic conditions.

Spalling, which can be classified into sub-surface and surface-originated types, is a major failure mode of rolling bearings due to rolling contact fatigue (RCF). Sub-surface originated spalling typically has a much longer life than surface-originated spalling, indicating that rolling bearings may often exhibit excessive durability in normal environments. Highly accurate prediction of bearing life for sub-surface spalling would enable the more active use of smaller products and contribute to resource conservation. ISO 281 provides a framework for integrated life prediction, taking into account the effect of lubrication conditions. However, it does not consider the effect of non-metallic inclusions, which can lead to sub-surface originated spalling. Previous studies have identified the mode II stress intensity factor (SIF) as the key driver of spalling initiated by internal defects such as inclusions, based on RCF tests with small artificial defects. Therefore, this study derives a life model using the range of SIF. Additionally, a novel and practical method that combines the life model with the statistical data on inclusion sizes is proposed to predict Weibull plots of spalling life.

Micro-pitting and wear phenomena were studied both experimentally and through simulation, focusing on the relationship between ball roughness and the lambda, Λ, value. The degree of damage due to micro-pitting and wear was investigated under different ball roughness conditions. Cross-sections of micro-pitting and wear were evaluated using optical microscopy, scanning electron microscopy (SEM), and electron backscatter diffraction (EBSD). Morphological observations revealed structures indicative of micro-pitting and wear fatigue, such as plastic flow and crack. In this study, plastic flow thickness, crack angle, and crack depth were used as indicators of the damage degree for micro-pitting and wear. The results from both experiments and simulations indicate that surface roughness contributes significantly to the maximum tangential stress that can initiate the plastic flow and cracks, particularly in micro-pitting. Additionally, the internal stress is expected to have a greater influence on crack propagation.

A previously published model that separates surface from subsurface survival is adapted for high temperature bearing steels and it is applied in life calculations for aircraft gas turbine mainshaft rolling bearings. This approach shows more realistic calculated life than current practices with the use of the method. Besides this, the proposed approach incorporates the effects of high temperature in the reduction of the fatigue limit, which is reflected in the life calculations, this can discriminate among steels working at high temperatures. As shown previously, with the separation of surface from subsurface, the effects from fatigue are quantified in the two separated zones and they can be compared, showing the zone of higher fatigue risk. Therefore, the proposed approach shows advantages in comparison with the current life calculation method used in the aircraft industry.

method. Besides this, the proposed approach incorporates the effects of high temperature in the reduction of the fatigue limit, which is reflected in the life calculations, this can discriminate among steels working at high temperatures. As shown previously, with the separation of surface from subsurface, the effects from fatigue are quantified in the two separated zones and they can be compared, showing the zone of higher fatigue risk. Therefore, the proposed approach shows advantages in comparison with the current life calculation method used in the aircraft industry.