Five different anti-wear additives, suitable for the formulation of environmentally adapted hydraulic fluids were tested, both commercially available and newly developed. The used base fluid was a high performance saturated complex ester. The formulated fluids' performance was evaluated through the use of an assembled pin & vee block in a modified Falex wear tester according to wear and frictional behaviour. The combinations of tested materials were steel-steel and bronze-steel tribopairs. The friction, wear scar volume and visual appearance both inside and outside the wear scar were studied. Some of the tested combinations gave unwanted performance, such as high friction, large wear and etching damages, whereas others gave good performance. It was found that the new additives showed promising results for formulation of environmentally adapted lubricants based on saturated complex esters. Further investigations will look closer at the chemical composition of the formed tribofilms with the use of surface sensitive analysis technology.

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Five different anti-wear additives, suitable to formulate environmentally adapted hydraulic fluids, were tested. The used base fluid was a saturated, environmentally adapted synthetic complex ester. The tested materials were steel-steel and bronze-steel. A modified Falex pin and a vee-block tester were used for the tribotests. XPS was used to characterize the surfaces. It was found that the new types of more polar additives work better than the traditional ones, though they can give selective transfer of cupper to the steel pin. To use this type of additives in fully formulated products more investigations have to be performed.

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The growth process and orientational degree of incremental-Ag films with a thickness of 5, 50 and 500 nm, respectively, on reoriented Ag (111) surface were studied by in-situ reflection high-energy electron diffraction (RHEED). The orientation of Ag grains for each incremental-Ag-film was also analyzed by synchrotron-orbital-radiated X-ray diffraction (SOR-XRD) to clarify the correlation between the film orientation and the incremental thickness by additional Ag deposition. RHEED observations showed that the incremental-Ag-film grows epitaxially on the reoriented-Ag (111) surface up to 500 nm in thickness. The Ag film, which grew on initial polycrystalline-Ag film, still showed a polycrystalline structure up to 50 nm in thickness, and the Ag (111) orientation is dominant at a thickness of 500 nm. The results of SOR-XRD analysis agreed well with those of RHEED. SOR-XRD analysis showed that the growth rate of Ag {111} grains in the polycrystalline film was also superior to that of other Ag {hkl} grains as the thickness increases. The degree of incremental film orientation increased as the incremental thickness increased, and the advantage in the high orientational degree of the incremental film on the reoriented Ag (111) surface was enhanced when the incremental thickness was within the nanometric range. A new method for selective growth of the epitaxial Ag layer using tribo-assisted reorientation was presented.

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In order to investigate the interaction between additives in metalworking fluids under difficult cutting conditions, tapping tests were conducted under different metalworking conditions for metalworking fluids consisting of liquid paraffin added with tricresyl phosphate (TCP), polysulfide (PS), and oleic acid (OA). The tapping torque was measured for tapping M6 threads in S45C steel by using workpieces designed with relatively small prepared hole for creating difficult cutting conditions. For evaluating the effect of metalworking fluids, two quantities - mean tapping torque (N_mean) and maximum tapping torque (N_max) - in the tapping torque signals were introduced. When one of the extreme-pressure (EP) agents, i.e., TCP or PS, is added into the liquid paraffin, both N_mean and N_max decrease considerably. Moreover, when both the EP agents are added, the values of both N_mean and N_max are smaller than those obtained for the same concentration of a single EP agent; this implies the synergy between TCP and PS. OA, when used with the two EP agents, does not always decrease the values of N_mean and N_max; there exists an optimal concentration level for TCP, PS, and OA for minimizing the values of N_mean or N_max.

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This paper describes time-frequency analysis of the friction coefficient with discrete wavelet transform. Ball-on-disk experiments were conducted with a steel ball, an aluminum disk and ethanol as a lubricant. The coefficient of friction was rather stable and low during initial sliding before it suddenly increased by seizure caused by loss of the lubricant. While no indication of transient change could be found before the seizure occurred in the original friction and ball displacement signals, the wavelet components of the friction coefficient clearly showed the local disturbances during several cycles before the sudden increase. The results suggest that the wavelet transform is potentially applicable to the prediction of catastrophic changes in friction.

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To develop lightweight wear-resistant titanium matrix composites, the wear behaviors of three kinds of composites produced from SiC and titanium (Ti-Si-C composite) and three kinds of composites produced from Si₃N₄, TiN and titanium (Ti-Si-N composite) were evaluated. The composites were slid against themselves without lubricant. The wear of these composites was smaller than that of titanium metal and was influenced by the kind of ceramics in the starting material rather than the amount of the ceramics. The wear resistance of the Ti-Si-N composite was higher than that of the Ti-Si-C composite. Tribo-oxidation took place on the surfaces of the composites during sliding, and the produced oxide abraded and hollowed the Ti-Si-C composite. On the sliding surface of Ti-Si-N composite, however, plastic flow of the oxide was observed.

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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.

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Lubricants with longer drain interval should be easy to maintain, economical, and environment friendly. Compact and high-performance machines require high-performance lubricants. Under these circumstances, alternative ashless additives exhibiting sufficient high-temperature stability and antioxidancy have to be developed. We have found that the addition of alkylated phenyl salicylates to the lubricants leads to good high-temperature detergency. In this paper, we report the factors affecting the high-temperature detergency of the alkylated phenyl salicylates and their utility.

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Diamond-like carbon (DLC) coating provides low friction properties without lubricants and, with lubricants, should provide super low friction. In this study, to find the possibility of the environment-friendly material combination that can provide super low friction (with a coefficient of friction lower than 0.01), the friction and wear properties of DLC coating with lubrication in sliding contact areas were evaluated. The friction and wear properties of the steel pin on DLC coated disk with lubrication were evaluated by using environment-friendly fluids (organic acid or alcohol) as lubricants. In the sliding test of tetrahedral amorphous carbon (ta-C) lubricated with DL(mixture of dextrorotatory and levorotatory molecules)-lactic acid, the super low friction coefficient, 0.01 was obtained at the end of the test, and was much lower than that of the uncoated disk and the a-C:H disk. And the coefficient of friction using DL-lactic acid was lower than that of acetic acid or glycerol. Then, the oxidation film (white layer) of FeO on the pin was formed under DL-lactic acid lubrication at the sliding surface of the pin. This showed that the condition of the steel pin also influenced the coefficient of friction. The main reason of reducing friction was thought that the carboxyl and hydroxyl groups in DL-lactic acid connected strongly with the dangling bond on the surface of the ta-C.

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Wear track profiles generated by pin-on disk wear tests under various test conditions were subjected to wavelet analysis and shown to have similar profile characteristics regardless of test conditions and materials. Specifically, the streaks in all wear tracks for both pins and disks showed similar characteristic scales of width and depth, thus making the appearance of individual wear tracks indistinguishable. These results suggest that there must be particular driving mechanisms of generating such characteristic scales of roughness.

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3-D finite element models of two types of PS type knee prostheses were constructed using their CAD data with use of a nonlinear spring model and an analytical load data for deep squatting. PS-type1 model was formerly used in total knee arthroplasty, and PS-type2 model is the latest version with a modified design of post structure. Stress analysis was then performed by an explicit finite element method under continuous flexion motion from 0 to 135 degrees with internal rotation up to 10 degrees. It was shown that the post/cam contact starts at about 65 degrees of flexion, and the equivalent stress rapidly increases due to the contact. Severe stress concentration is also generated on the Post surface due to the post/cam contact. This kind of stress concentration may cause damage and failure of the post. It was clearly shown that the design modification applied to PS-type2 effectively reduced the stress concentration of the post.

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A numerical study of adhesive contact between rough surfaces with soft coating is presented using an elastic-plastic model of asperity contact deformation. The analysis considers the elastic and plastic deformation of both the coating and the substrate unlike the work available in literature where the coating is considered to be in pure plastic contact. The JKR (Johnson-Kendall-Roberts) adhesion model is used and the well-established adhesion indices (elastic and plastic adhesion indices) are utilized to consider the different conditions of varying load and material and surface properties of the substrate and the coating. Contact load and contact area are obtained as functions of mean separation between surfaces for different combinations of adhesion parameters, material properties and thickness of the coating. The effects of these parameters on contact behavior of coated surfaces are investigated. For thin coating and light loading, contact is strongly influenced by the existence of soft coating that increases the contact area due to plastic deformation of the coating.

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