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Copper alloys have been used for plain bearing material in many kinds of engineering machines. In this study typical copper alloys are selected from the view point of strength and thermal conductivity that is proportional to electric conductivity. The aim of this study is to investigate that the thermal conductivity is very important character to keep mild friction with appropriate condition of block-on-ring tests. The results show that the patterns of friction coefficient of time are classified into four types. Type I is stable in low friction. Type II is slightly up in the end part. Type III is less stable and up to 0.4 level of friction coefficient (μ). Type IV is rough waving in more over 0.4 level of friction coefficient (μ). The materials of Type I are chromium copper alloy and Corson copper alloy. The Type II is beryllium copper alloy. These Type I & II alloys have the same properties of high thermal conductivity and characteristic microstructure of dispersed hard particles in copper matrix. High thermal conductivity reveals good tribological performance, i. e., low friction and wear. Moreover after tribological test, the surface of these alloys changes and transformes to rich oxide surface with condensed hard particles. It’s action is simple application of friction steps to escape the severe wear. Especially the copper alloy with ferrous particles dispersed in matrix makes severe mode of friction by the same element of friction.

Diamond-like carbon (DLC) coatings continue to attract attention for their low friction and high wear resistance. The transferred or transformed layer, which has a high sp2 carbon content induced by cyclic friction, results in an ultralow friction coefficient in ambient air. However, there are few reports on such layers, especially the transformed layer in oil lubrication, because this transformed layer could be too thin to be measured quantitatively. M. Kano and C. Matta reported the 3 nm thickness of a sp2 carbon layer using EFTEM study. The spectroscopic reflectometry technique has been applied to measure the thickness of the transformed layer of the DLC's wear scar after friction under oil boundary lubrication. The purpose of this study was to develop a quantitative method for measuring the thickness of the transformed layer in hydrogen-free DLC (ta-DLC) and two types of hydrogenated DLC coatings. Then, we clarified the friction model of these DLC coatings under oil lubrication as the transformed layer was the solid lubricant film. Consequently, we observed that there were optimum ranges of wavelengths and optical models for measuring the transformed layer of the DLC. The optimum wavelength range was 300–500 nm, and the bi-layer model was the best for DLC1, which was the hydrogen-free DLC. For the thicker and un-transmissive coatings, which were hydrogenated DLC coatings, the ranges of wavelengths were 600–800 nm, and the optical model was hypothesized to be a single-layer model. From these optical models, we observed that the thicknesses of the transformed layers of the DLC coatings under oil boundary lubrication were approximately 10–200 nm in the hydrogen-free DLC and 0–200 nm in the hydrogenated DLC. From the analysis of the thickness of the transformed layer and surface roughness, σ⁎, of various DLC coatings, we observed that the friction coefficient of the DLC under oil boundary lubrication was determined by the possibility of breaking the transformed layer. This result strongly suggested that the DLC film was a material that realized self-surface modification. We believe that the results of this study could be developed as a guideline for designs of surfaces with DLC coatings.

Diamond-like carbons (DLC) with different hardness of 47.1, 11.8 and 6.05 GPa were coated on SUJ2 rollers, and their tribological properties were investigated under boundary lubrication conditions in an additive-free mineral base oil at different testing oil temperatures of 24, 80 and 160 °C. The hardest DLC with 47.1 GPa showed the lowest friction coefficient and wear. From the results of the Raman analyses and spectroscopy ellipsometry, we found that the structure changed at oil temperature of thickness of 80 °C with the formation of a thick layer of 160 nm at the topmost sliding contact surface which provided the lowest friction coefficient of 0.03 in an additive-free mineral base oil.

Acoustic Emission (AE) technique, which has detection capability for minute failures, has been tried to monitor the condition of a plain bearing under the laboratory conditions. In this paper, the bearing materials for marine diesel engines – tin alloy as known as “white metal”, aluminum alloy of 40% tin mass and aluminum alloy 40% tin mass with resin overlay – were tested using a sleeve-to-plate tribo-tester. The frictional force and back temperature were measured as well as the AE signals. The possibility of AE technique to monitor the bearing condition was also assessed by evaluating tribological properties under different operating conditions such as start–stop simulating the crankshaft turning during engine assembly and seizure tests. These results indicate that AE is useful for monitoring the lubricated condition of the sliding surfaces and evaluating tribological properties of the bearing.

This paper describes the excellent frictional properties of a newly developed lead-free aluminum alloy bearing with a low frictional layer on its inner surface, which consists of a molybdenum disulfide (MoS2) layer deposited directly without any binders such as resin. The thickness of the layer is in sub-micron levels. This bearing has high potential in reducing the friction losses within an automotive engine in pursuit of better fuel economy. Scratch tests under dry conditions clearly showed that the newly developed bearing exhibited less adhesion at higher load compared to current materials. In addition, the microscopic observation of the scratched surfaces demonstrated that the MoS2 layer and its transferred film existed on both the bearing surface and the depressor surface, respectively. Measurements of the coefficient of friction on stop–start bearing tests confirmed that the newly developed material lowered friction and also shortened time to running-in under start–stop operation experienced in recent automotive engines. Observation of the sliding surfaces clarified that the surface layer of MoS2 gave lower adhesion, resulting in lower coefficient of friction.

The tribological properties of poly(ether-ether-ketone) (PEEK) against steel was evaluated by a ring-on-flat type tribo-test under rotating motion. Addition of poly(tetrafluoroethlene) (PTFE) as solid lubricants improved the load-carrying capacity of the material. The role of PTFE was studied by means of time of flight secondary ion mass spectroscopy (TOF-SIMS). The transfer of PTFE from the PEEK surface onto steel surface was found to be beneficial for preventing seizure.