Masabumi Masuko

Composite coatings of nickel and ceramic particles prepared in two steps

Abstract A simple technique has been proposed in order to disperse a high vol.% of ceramic particles into a nickel matrix in two steps. A uniform film of ceramic particles was first electrophoretically deposited on an iron plate. Nickel was then electrodeposited in the second step onto the substrate covered with the film of these ceramic particles. Using 5 g/dm 3 of particles in the electrophoretic bath, the two-step method enabled us to incorporate 63 and 67 vol.% of Al 2 O 3 and BN particles, respectively, into the nickel matrix. Similarly, using a mixture of 5 g/dm 3 of BN and 2.5 g/dm 3 of Al 2 O 3 particles in the electrophoretic bath, the proposed two-step method enabled us to incorporate 55.5 and 6.2 vol.% of BN and Al 2 O 3 particles, respectively, into the nickel matrix. In the present investigation, the wear resistance of the coatings was examined under dry sliding conditions using the ball-on-disk configuration. For the reference, an iron plate was coated with the Ni/BN and Ni/Al 2 O 3 composites in a single step. The content of BN and Al 2 O 3 particles in these coatings were 18 and 8.4 vol.%, respectively. The wear experiments showed that, regardless of the method of preparation, the Ni/BN composite coatings had a better wear-resistant performance than the Ni/Al 2 O 3 coatings. However, all three composite coatings prepared by the two-step method showed substantially better wear resistance than those prepared by the single-step method. It has been assumed here that the better anti-wear performance of the composite coatings prepared by the two-step method is due, not only to the higher volumetric content of the particles, but also to the manner in which these particles were incorporated within the metal matrix.

Dynamic Behavior of Surface-Adsorbed Molecules Under Boundary Lubrication

Friction under boundary lubrication was measured using a pendulum-type friction machine. Long straight-chain fatty acids with even carbon numbers, amine, and alcohol were used as additives, and n-hexadecane was used as the base oil. Effect of the temperature, chain length of additives and additive concentration were investigated. The phenomena obtained under 373 K were as follows: 1) “Transition concentration” wherein a drastic change of friction coefficient appeared were observed. 2) “Transition concentration” of amine or alcohol solutions appeared at higher concentration than that of acid solution. 3) In “high concentration region,” the friction coefficient gradually increased with the decrease of the concentration. 4) Temperature raise caused a high friction coefficient. 5) Friction coefficient gradually decreased with an increase in chain length. 6) “Transition concentration” shifted toward low concentration with an increase in chain length. 7) No chain-matching effect was observed. These results are ...

Influence of lubricant additive and surface texture on the sliding friction characteristics of steel under varying speeds ranging from ultralow to moderate

A newly developed tribometer that undergoes significant changes in sliding speed, ranging from ultralow (5 μm/s) to moderate (17 cm/s), was used to study the lubricated friction characteristic of steel. In this study, the friction characteristics of stearic acid-formulated oil were studied to clarify the effects of surface roughness or surface roughness texture on friction. Several kinds of specimens having isotropic and anisotropic surface roughness with different textures were used. For an isotropic surface, a rougher surface resulted in low friction under low-speed conditions. The same surface produced high friction under high-speed conditions, where macroscopic hydrodynamic action was predominant. Remarkably less friction was observed in the transverse than in the longitudinal direction when the specimen had anisotropic roughness. This difference was particularly notable under ultra-low-speed conditions. Two other parameters of skewness and kurtosis of roughness distributions show that low friction was obtained when surface roughness distribution approached normal. It appears that the low friction observed with a rough surface or a transverse roughness direction could be explained by the microscopic hydrodynamic action of fluid together with the lubricity of the adsorbed molecular layer.

Comparison of Sliding Speed Dependency of Friction between Steel Surfaces Lubricated with Several ZnDTPs with Different Hydrocarbon Moieties

Abstract This article describes the friction characteristics of zinc dialkyldithiophosphates (ZnDTPs) with different hydrocarbon moieties. A newly developed tribometer was used for the precise measurement of friction by alteration of the sliding speed from ultra-low to moderate. Four types of ZnDTPs (sec-C3C6, sec-C6, prim-C8, and prim-C12) were used as additives to measure friction between steel surfaces. Several phosphorus compounds were used as references. Auger electron spectroscopy analysis and micro-FT-IR reflection adsorption spec-troscopy analysis were employed to elucidate the chemical composition and chemical structure of tribochemically reacted films on steel surfaces. The results demonstrated that a remarkable difference between friction characteristics was observed among four ZnDTPs with different hydrocarbon moieties and that friction decreased with increasing alkyl chain length of ZnDTPs at lower speeds. These results accounted for the observation that the friction characteristics of ZnDTPs were influenced by their respective hydrocarbon moieties.

High-pressure viscosity prediction of di(2-ethylhexyl) phthalate and tricresyl phosphate binary mixtures using dielectric relaxation data

Abstract Dielectric permittivity and loss in di(2-ethylhexyl) phthalate and tricresyl phosphate binary mixtures were measured over a frequency range from 100 Hz to 1.5 MHz under high pressure. The mixtures showed single dielectric relaxation. The composite plots of the dielectric loss data showed one master curve and time–temperature–pressure superposition were applicable. The prediction of high-pressure viscosity was carried out from the change of dielectric relaxation time with temperature and pressure. The predicted results showed relatively good agreement with viscosity data obtained from a falling-sphere viscometer.

Pressure-dependence of dielectric relaxation time in poly(propylene glycol) and its application to high-pressure viscosity estimation

Dielectric permittivity and loss of poly(propylene glycol) with different molecular weights (400–3000) and terminal groups (OH and CH3) have been measured in the frequency range of 100 Hz to 1.5 MHz. Measurements were conducted over the temperature range 202–293 K under atmospheric pressure and 283–320 K under pressure up to 600 MPa. Two relaxation processes, one with strong absorption in the high-frequency region (α-relaxation) and the other a weak process in the low-frequency region (α′-relaxation), were observed for the OH-terminated samples having molecular weights above 2000 and for all the CH3-terminated samples. Most of the experimental data under high pressure showed a nonlinear decrease in the logarithm of the frequency of maximum dielectric loss with increasing pressure. The pressure-dependence of the dielectric relaxation time of the α-process was analyzed by several models based on the free-volume concept. The regression results of dielectric relaxation time as a function of pressure were applied to the estimation of high-pressure viscosity. The predicted viscosity showed relatively good agreement with viscosity data obtained from a falling-sphere viscometer.

Influence of Chemical and Physical Contaminants on the Antiwear Performance of Model Automotive Engine Oil

Abstract The antiwear performance of simulated used-engine-oil that contained a chemical contaminant (degraded zinc dialkyldithiophosphate (ZnDTP)) was studied with and without physical contamination (carbon black) using a four-ball tribometer. By reacting with cumene hydroperoxide, sec-C6-ZnDTP was degraded and produced many compounds containing both phosphorous and sulphur. The simulated used-oils were found to promote wear. This wear was considered to be due to corrosive wear by the excess reaction of surfaces with the sulphur contained in the degraded compounds. Carbon black was used to model carbon soot, which is another key substance of degraded engine oils, especially in diesel engines, to study the synergism between chemical contamination (ZnDTP degradation) and physical contamination (carbon soot contamination). Carbon black increased wear irrespective of the level of ZnDTP degradation, and the acceleration was much greater in the degraded oils. The wear acceleration by carbon black was observed even when the antiwear film from ZnDTP was already present on the surface. It was suggested that the wear acceleration by carbon black was due to abrasion.

Oxidative Degradation of Mineral Oil under Tribocontact and Ineffectiveness of Inhibitors

Oxidative degradation of mineral oil under tribocontact is investigated in comparison with static oxidation. A rolling four-ball apparatus lubricated with a small amount of sample oil (approximately 10 mg) was selected as the method for degrading oil samples. Applications of very small amounts of sample oils made it possible to detect small amounts of degradation product after friction tests. An FTIR analysis and gel permeation chromatography were used to characterize the degraded oils. It was found that mineral oil oxidatively degraded during tribo-operation at nominally moderate temperatures. The effect of oxidation inhibitors on the tribodegradation of mineral oil was investigated. A hindered phenol inhibitor, which acts as a radical scavenger, and a sulfur compound inhibitor, which acts as a hydroperoxide decomposer, were used. No inhibition was observed in the tribodegradation of mineral oils with either of two inhibitors, though they were effective for the static oxidation. It was also found that th...

Elucidation of the Antiwear Performance of Several Organic Phosphates Used with Different Polyol Ester Base Oils from the Aspect of Interaction between Additive and Base Oil

The antiwear performance of organic phosphates, such as tricresylphosphate (TCP), tributylphosphate (TBP) and diphenylhydrogen-phosphate (DPHP), dissolved in several polyol esters is studied. Several trimethylolpropane esters (TMP) and pentaerythritol esters (PE) having different carbon chains were used as base oils. A four-ball tribometer was used to determine the antiwear performance of oils, using commercially available bearing steel balls as test specimens. Although the wear of steel was drastically reduced with low-concentration solutions of these phosphates, the wear increased with increasing concentration in the higher-concentration region. All of the phosphates showed characteristics of an optimum concentration for minimizing wear. This behavior can be attributed to the effective adsorption/reaction of phosphates in the low concentration region and the reaction forming excess inorganic phosphates on the surface that causes corrosive-like wear in the high-concentration region. Different polyol esters showed different optimum concentrations of the additive. The order of optimum concentration among the polyol esters was different with different phosphates. Although the wear rate absolute values at the optimum concentration did not show clear correlation, it is shown that the effect of the concentration of additives on the antiwear performance can be explained by the interaction between additives and base oils using the solubility parameter.

Tribochemical Surface Reaction and Lubricating Oil Film

A radioactive tracer technique was used to investigate a tribo-chemical surface reaction obtained by a thrust collar type friction Machine. Radioactive dibenzyl disulfide labeled with sulfur-35 was used as an additive. Steel and copper disks were used as friction specimens. Radioactive copper sulfide on the friction surface was quantitatively measured with a G-M tube, and a kinetical analysis of the reaction was carried out. The friction coefficient decreased linearly depending on the amount of surface produced on the friction surface. This dependency was accompanied by adsorption of dibenzyl disulfide, which made a more effective lubricating oil film and was enhanced by the sulfide on the friction surface. The results of kinetical analysis were explained effectively by considering the oil film behavior related to the adsorptive action of the surface sulfide. Presented as an American Society of Lubrication Engineers paper at the ASLE/ASME Lubrication Conference in Kansas City, Missouri, October 3–5, 1977