In this study, hydrogen formation was investigated during lubrication tests, which were carried out with synthetic hydrocarbon oil under high-vacuum conditions using disks made of Fe, Cr, SUS304, SUS440C, and SUJ2. The evolved gases were detected using a quadrupole mass spectrometer. Hydrogen evolution was observed at the beginning of the sliding. Hydrogen and hydrocarbons were formed simultaneously after 1 km of sliding distance. The hydrocarbon oil was decomposed tribochemically by the same point. When SUS304 was used as the specimen, a higher rate of hydrogen evolution was observed at the beginning of the sliding action compared to the other metals. X-ray photoelectron spectroscopy of the disk surface revealed that there was a thicker oxide film and large amount of chemisorbed water on SUS304. These results suggest that the chemisorbed water on SUS304 could be a source of hydrogen. When the SUS304 specimen was pretreated with heavy water, hydrogen deuteride ion was detected during the lubrication test. It can be concluded that chemisorbed water on metal surfaces is a source of tribochemically-formed hydrogen during lubrication tests. The sharp decrease in hydrogen evolution at the beginning of sliding is related to the destruction and removal of the oxide film.

An investigation was conducted of the low-friction and low-wear mechanism of the adsorbed layer formed by dibasic acid ester derivative. First, the film thickness and film density of the adsorbed layer on an iron surface was evaluated by neutron reflectometry. The density of the adsorbed layer formed at 25°C was twice that at 100°C. The macroscale tribological properties of an adsorbed layer formed by dibasic acid ester derivative and its constituent additives (succinic acid and amine) were evaluated using a ball-on-disk tribometer at 25°C and 150°C. The derivative exhibited low friction and wear properties even at high temperature. To clarify the mechanism of the excellent low friction property, nanoscale tribological testing was conducted using an atomic force microscope. The precise measurement indicated that the dibasic acid ester derivative initially exhibits low friction due to generation of metal soap from the amine, and then subsequent friction generates metal soap from the succinic acid that has superior friction reduction performance, which promotes lower friction, especially under low-contact-pressure sliding conditions.

The Walther equation is often used for the viscosity temperature characteristics of lubricants. However, it was found that it cannot be applied to high pressure viscosity. In this study, the relationship between viscosity, temperature and pressure was analyzed. As a result, viscosity at each pressure was found to be negatively proportional to the square of temperature, and linear equations converges at absolute zero were derived. In parallel, a thought experiment was conducted on the viscosity of ideal liquid. It was found that the absolute zero viscosity (η_t=0) of ideal liquid is constant regardless of the pressure. This is consistent with the convergence point at absolute zero of the linear equation in the above analysis. Furthermore, a high pressure viscosity temperature linear equation incorporating the pressure was derived. This eqaution is a van der Waals type viscosity equation consisting of three intrinsic constants: absolute zero viscosity η_t=0 [mPa·s], viscosity constant 1/B [GPa/K²] and pressure constant C/B [GPa]. It was found that this is liquid viscosity equation. This equation is also ideal liquid viscosity equation. Furthermore, C/B was found to be equivalent to P_R [GPa] of liquid state equation. By this, the high pressure viscosity of lubricant can be estimated from the derived van der Waals type viscosity equation.

The axial loads of high-speed rotating turbo machines are supported by self-acting hydrodynamic components known as air foil thrust bearings (AFTB). The load bearing capability of these bearings depends primarily on the foil structure and secondarily on the operating conditions. The present review enlightens on the tribological performance parameters of the said bearing in enhancing the load carrying capacity. Various design and fabrication methods including theoretical models are briefly summarised and comparisons of experimental results are presented in order to reveal the possible research gap that leads in optimising the gas lubricated foil thrust bearings (GFTB) for their better employment in typical applications.

In this study, slipper/swash plate sliding test rigs were developed to measure oil film thickness distribution. For this purpose, fluorescence measurement was performed with a sapphire glass swash plate and a light emitting diode as the light source. The oil film thickness distribution was measured under various conditions by varying the rotation speed and the oil pressure supplied to the cylinder. The shape of the swash plate matched the oil film thickness distribution measured via the fluorescent method, thereby confirming the validity of the measurements. Furthermore, the maximum tilt azimuth angle of the slipper turned outward as the rotational speed increased.

In this paper, based on the tribological characteristics of rolling bearing greased, we employ X-ray fluorescence spectrum analysis to study the effect of wear in cage with brass, iron and nylon as the main materials. We are especially interested in revealing the relationship between the wear of cage and the wear of rolling bearing parts. Statistical data results show that cages made of different structures or materials always have a certain degree of wear in the operation of grease lubricated bearings. In addition, the wear of the cage is usually less than that of the bearing rolling parts. Our research also indicates that wear particles from different cage materials impose significantly different influences on bearing and grease. Among those cage materials, the influence of the wear particles from nylon cage is more reflected as the mechanical action of the hard filler in the polymer cage. As a comparison, for the iron cage, since its wear particles have metal activity and catalytic properties, they also play important roles in both accelerating the chemical oxidation process of the grease and damaging the network structure of the grease thickener beside the abrasion.

In order to suppress electric wear of current collecting materials such as a contact wire and a contact strip in an electric railway, it is necessary to estimate the relationship between current and melting volume at a contact loss point. In this paper, we focused on a molten bridge which is considered as the main factor of electric wear at the contact loss point. And we proposed the estimation method of melting volume of contact wire and contact strip; in which film resistance is considered by using the relationship between the electric potential and the temperature at the contact spot. From estimation results, it is found that the melting volume increases as current increases, and that it increases as a contact boundary factor decreases. In addition, the authors carried out wear tests and measure a melting depth, a melting radius, and a melting volume under two conditions of current. From wear test results, experimental values of melting volume of the contact wire were in the range where contact boundary factor α was estimated from 0.90 to 0.94.

In oil refineries and petrochemical industries, a containment seal (CS) can be applied to a flashing hydrocarbon pump as a sealing device to prevent environmental pollution. It is extremely difficult to design a CS to ensure the contradictory functions of fluid-tight sealing and sealing-surface wear resistance, which are required under both conditions of dry running in gas and wet running in liquid. In this study, a new CS design concept, “CSAM” (Containment Seal by Additive Manufacturing), for the sealing surface and internal structure of a sealing ring was developed by additive manufacturing. A lubrication film formed on the sealing surfaces of mechanical seals is maintained by the opening force (OF) with fluid pressure and the closing force (CF) with fluid pressure and spring load. To obtain the desired OF, the CSAM controls the pressure distribution across the sealing surfaces by introducing outside pressure through slots on the sealing surfaces, and an annular cavity is formed within the sealing ring. Based on a series of numerical analyses and static tests, it has been found that the difference between OF and CF can be properly controlled using slot design parameters. The results suggest the possibility of achieving the contradictory functions of sealing and wear resistance under both the gas and liquid conditions required for CSs.

The internal combustion engine will be required as a bridge-technology in the upcoming decades to achieve a significant reduction in local emissions in the mobility, and logistics sector. Alternative fuel technologies will present new mechanical engineering challenges, including increasing efficiency and reducing mechanical losses. Textured surfaces with appropriate manufacturing parameters can enhance lubrication, and reduce friction in sliding and rolling contacts, e.g., journal bearings, or the piston ring – cylinder subsystem. This paper gives an overview of 80 scientific works related to laser surface technologies, with an emphasis on surface texturing for friction reduction from the viewpoint of engine development. The most common texture types, further directions, and general challenges are highlighted in the summary.

Aluminum alloy sliding components are widely used in internal combustion engines. However, aluminum easily adheres to the countersurface, resulting in high friction. Hence, laser irradiation was used to oxidize the aluminum surface and promote tribofilm formation using molybdenum dithiocarbamate and zinc dialkyldithiophosphate (ZnDTP). This study investigated laser irradiation to reduce friction between steel balls and aluminum disks in fully formulated engine oil. Laser scanning was used to create 100-μm-pitch concentric circles on the disks. The friction behavior was classified into two modes: no friction reduction (mode-I, μ: 0.09–0.12) and friction reduction after the high-friction period (mode-II, μ: 0.06–0.09). Friction mode transition occurred when the laser energy density exceeded the critical value (E_c). Energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy showed that, for mode-I, aluminum adhered to the ball, and no sulfur-containing tribofilm formed. For mode-II, the ZnDTP-derived phosphate film formed on the disk suppressed aluminum adhesion, and a sulfur-containing tribofilm formed on the ball. Micro-Vickers tests and X-ray diffraction showed that an amorphous/nanocrystalline structure formed in the unirradiated area owing to heat diffusion under high-energy-density laser irradiation (>E_c). Results suggest that metallographic structural change in the unirradiated area promotes ZnDTP reactions, causing the mode transition.

Heat-assisted magnetic recording (HAMR) is expected to be a realistic next-generation technology for increasing the recording density of hard disks. However, the magnetic layer is heated above the Curie temperature, and, as a result, the heated lubricant is desorbed from the disk by decomposition and evaporation, which causes a problem as it adheres to the air-bearing surface (ABS) as a smear. In this study, pyrolysis gas chromatography/mass spectrometry (Py-GC/MS) analysis was performed in helium and air environments to investigate the decomposition mechanism of perfluoropolyether (PFPE) lubricant D-4OH by heating and in the presence of oxygen. In the helium environment, thermal decomposition of the end groups was confirmed at 350°C and above with a possibility of main chain decomposition at 450°C. In the air environment, decomposition of the end group was confirmed at 250°C and above, and decomposition of the main chain was confirmed at 450°C. Experiments using a pin-on-disk tester were conducted to confirm what happens to the area of smear when a thin film of D-4OH lubricant coated on an actual disk is laser heated. As a result, it was confirmed that the area of smear decreased even at an oxygen concentration of 5%.