The International Tribology Conference Hiroshima 2011 was held from Sunday 30^th, October to Thursday 3^rd, November, 2011 at International Conference Center Hiroshima, Japan. A total of 650 delegates from 29 countries including 150 delegates from overseas gathered in Hiroshima. A total number of papers presented at the conference were 418, which included 4 plenary lectures, 302 oral presentations and 112 poster presentations.

The papers presented at the International Tribology Conference Hiroshima 2011, and submitted to the Tribology Online have subsequently undergone the normal peer-review process by multiple reviewers. Accepted papers are published in two separate issues of Part I and Part II. This issue is its first issue. The second issue is going to be published as soon as the peer-review and the editorial processes of the papers are finalized.

View full abstract

We investigated the nano-scale superlubricity or ultralow friction appeared at the graphene/C₆₀/graphene interface, where the (mean) lateral force becomes nearly zero within the atomic resolution of the frictional force microscopy (FFM). The C₆₀ intercalated graphite film is one of the most successful systems we have developed as the graphene/C₆₀/graphene interface, and it exhibits an excellent friction coefficient, μ<0.001. Simulated superlubricity of the graphene/C₆₀/graphene interface shows the marked anisotropy with a period of the scan direction of 60°, which reflects the symmetry of the six-membered rings of the C₆₀ molecule and graphene sheet. The physical origins of the maximum peak and near-zero minimum are numerically clarified. Controlling supelubricity of the graphene/C₆₀/graphene interface will contribute to solving the energy and environmental problems.

View full abstract

The deformation-wear transition map of hydrogen-free amorphous carbon coating (commonly known as Diamond-Like Carbon (DLC)) is intended to graphically distinguish between the plastic deformation and impact wear of DLC coating, as well as, to predict its transition points under cyclic impact loading. In this study, besides the maximum normal impact load, other promising parameters that would induce the wear of DLC coating, have been proposed for future developments of a deformation-wear transition map. This study was carried out by impacting a DLC coated tungsten high speed steel (SKH2) disc, with a chromium molybdenum steel (SCM420) pin, at up to 10⁵ impact cycles. All impact tests were conducted at room temperature under lubricated conditions. The preliminary results suggest that impact velocity can also contribute to the wear of DLC coating as a result of its phase transformation.

View full abstract

DLC coatings are low friction and low wear coatings and thus inherently possess some of the characteristics that may be beneficial or even enable green lubrication requirements. In particular, their low wear behavior may represent a potential for different, less harmful and more environmentally adapted lubrication compared to conventional materials, which may become an attractive approach for novel green technologies in various mechanical systems. In this work, we present some of several possible strategies for designing green lubrication, focusing only on concepts that are well-suited and enabled in a combination with specific properties of DLC coatings. These may include approaches through predominantly chemical-based interactions, physical-based lubrication technologies, and a combination of both, i.e. physical-chemical properties.

View full abstract

Diamond-like carbon (DLC) is considered to be predominantly amorphous, whereby small clusters of microcrystalline structures with sp³ and sp² bonding, and an amorphous matrix, coexist. DLC film has some extraordinary properties such as high hardness, low friction, and high wear resistance. There is strong demand for the use of such DLC properties in a wide range of tribological applications, including cutting tools, mechanical elements of automobiles, die surfaces, and computer hard disks. On the other hand, it is widely known that changes in the structure of DLC film during sliding affect its tribological properties. However, the precise mechanism of the structural change remains unclear. In this study, the effects of applied heat and stress on the structural changes of DLC films were investigated to evaluate the predominant factor in this mechanism. DLC film was deposited on a steel substrate using plasma-based ion implantation and deposition. After heat treatment with applied force, structural changes of the DLC film were investigated by micro-laser Raman spectroscopy. Structural change was confirmed in DLC film annealed at temperatures over 648 K. This suggests that hydrogen evolution from the DLC film possibly caused the structural change. Greater hydrogen evolution was observed from the unloaded surface compared to the loaded area. Structural change was found to be dependent on the stress field: The tensile stress led to structural change, but the compressive stress field did not affect the structural change. These results indicate that a structural change in DLC film caused by heat treatment can be suppressed by preventing hydrogen evolution from the surface of the film.

View full abstract

We in-situ observed the deformation of a gold single real contact point at the nanoscale during friction experiment in order to reveal the mechanism of friction. In this experiment, a special experimental setup combining between micro-electro-mechanical system (MEMS) and transmission electron microscope (TEM), called MEMS-in-TEM, was utilized for the stable visualization of the real contact point. Gold tips with electrostatic actuators were gently brought into contact and were rubbed each other at a quasi-static speed under TEM observation. Between tips, the gold single real contact point was formed and deformed in shear. During this deformation, the ends of the real contact point travelled 2.8 nm along the surface of the gold tips, although those of silicon and silver did not move. The maximum friction was 60 nN, repeating the stick-slip behavior from 35 to 60 nN. This result will be helpful to understand the mechanism of friction at the nanoscale and the lubrication mechanism of solid lubricants.

View full abstract

Driven by diminishing fossil fuel resources, global warming and subsequently rigid legislation on CO₂ emission, fuel economy is a major challenge for the automotive industry. Each element of the powertrain has been optimized or newly designed to increase efficiency. In this optimization process the engine oils and transmission fluids are important design elements and their contribution to improved efficiency is significant. Polyalkylmethacrylates (PAMAs) are widely used as viscosity index improvers in engine, transmission and hydraulic oils. They have been shown to adsorb from oil solution onto metal surfaces to produce thick and viscous boundary films. These films are maintained even in low speed and high temperature conditions and thus produce a reduction of friction and wear. It was found that specifically designed film-forming PAMAs can improve pitting performance of lubricant formulations. The paper describes the impact of tailor-made functionalized PAMAs on boundary film formation and explores their ability to increase the fatigue life of lubricants.

View full abstract

The vertical-objective-based ellipsometric microscope (VEM) is expected to be a useful method for clarifying the lubrication phenomena that uses thin liquid lubricants, especially the lubricant for hard disk drives (HDDs). Although the feasibility of VEM for thin lubricant films was confirmed, the designs for the optical system and image detection have not been established. In this report, the optical design of the VEM is presented, as well as the method of controlling the coherent noises and improving the thickness resolution is discussed. By our method, the thickness resolution of VEM can be improved to 0.4 nm, and the real-time observation of sub-nm-thick thin liquid lubricant films can also be achieved.

View full abstract

We measured the frictional coefficient under banana skin on floor material. Force transducer with six degrees of freedom was set under a flat panel of linoleum. Both frictional force and vertical force were simultaneously measured during a shoe sole was pushed and rubbed by a foot motion on the panel with banana skin. Measured frictional coefficient was about 0.07. This was much lower than the value on common materials and similar one on well lubricated surfaces. By the microscopic observation, it was estimated that polysaccharide follicular gel played the dominant role in lubricating effect of banana skin after the crush and the change to homogeneous sol.

View full abstract

Lubricants for metal V-belt type CVTs (B-CVTFs) must be able to produce a higher metal-metal friction coefficient and give excellent anti-shudder properties for lock-up clutch used in B-CVTs. This study intends to optimize various kinds of lubricant additive such as anti-wear additive, detergent and friction modifier (FM) for improving these performances of B-CVTs. In addition, contact mode atomic force microscopy was utilized to investigate links between friction performance and the morphology of tribofilms formed from candidate additives. As a result, an additive formulation consisting of a phosphorus additive, calcium detergent and dispersant showed a higher friction coefficient between the metals. The results of the surface analysis on the wear scar indicate that calcium tribofilm species formed fine depositions on the rubbing surface, which might attribute to a higher friction between the metals. Moreover, it is found that a sort of friction modifier gave an excellent anti-shudder performance for wet clutch with keeping higher friction coefficient between the metals, which would result in improving the performance of B-CVTs.

View full abstract

The present preliminary study examined whether an increase in the lateral width of footwear (base-of-support width) can reduce the risk of falling caused by induced lateral slip while turning on slippery surfaces. Wide base-of-support (BOS) footwear was designed and manufactured, with lateral widening achieved by fixing a BOS extension, using a planar linkage of 70-mm width on the lateral side of normal BOS footwear. Gait trials were conducted on 16 young healthy male adults. Subjects were instructed to walk in a straight line and to turn 60° to the right on a stainless steel floor covered with glycerol solution. As compared with the normal BOS footwear, the wide BOS footwear reduced the frequency of trials in which fall occurred due to lateral slip by up to 67% and the slip distance and slip velocity of the supporting foot were reduced by up to 40% and 35%, respectively. The results demonstrated the efficacy of increased lateral BOS width in reducing the risk of fall caused by induced lateral slip.

View full abstract

The dielectric spectroscopy method was applied to the investigation of the dynamics of base oil and thickener of lubricating grease. In order to observe the dielectric relaxations both of base oil and thickener, the lubricating grease formed from polyol ester base oil and lithium 12-hydroxy stearate thickener was prepared. Apparent viscosity, dynamic viscoelasticity and creep properties were measured, and the temperature characteristics of these rheological properties were compared to that of dielectric relaxation time. Prepared lubricating grease showed two dielectric relaxation processes. The dielectric relaxation observed in low-frequency and high-frequency regions were attributed to thickener and polyol ester base oil, respectively. The dielectric relaxation time of the high-frequency relaxation exhibited non-Arrhenius-type temperature dependence. This temperature characteristic is similar to that of viscoelastic relaxation time, shift factor obtained from superposition of creep compliance data, and viscosity of polyol ester base oil. On the other hand, the dielectric relaxation time of the low-frequency relaxation showed Arrhenius-type temperature dependence. However, no clear relation was observed between the dielectric relaxation in low-frequency region and the rheological properties measured in this study.

View full abstract

In the present study, a nine-recess hybrid journal bearing (HJB) having a Young Leaf Mark recess was operated at a rotational speed of up to 75,000 rpm using the cryogenic journal bearing test apparatus at JAXA, to clarify an onset speed of the rotor instability supported by the cryogenic HJBs. Liquid nitrogen was supplied to the test bearing with a pressure of up to 4 MPa. The test bearing is 60 mm in diameter, 25 mm in width, with a 0.055-mm clearance and a recess area ratio of 0.186. When the HJB was operated at a rotational speed of over 74,000 rpm in liquid nitrogen, hard frictional contact between the bearing surface and the journal surface occurred, which consequently caused considerable damage to the Cr₂O₃ coating film on the journal. The results confirmed that the HJB surface damage had relatively little effect on HJB performance. Therefore, cryogenic HJB tested can be considered to have sufficient robustness when the rotational speed is below 60,000 rpm.

View full abstract

Crushing of minerals involves several wear mechanisms. The mineral medium increases the complexity of the wear process by introducing many new variables. Despite the fact that processing of minerals normally causes wear, the minerals can also in some cases decrease the extent of wear. The comminution products, for example, can decrease the wear rate in abrasive wear during high-pressure grinding. The aim of this work was to study the effect of embedded quartz on abrasive wear of wear resistant steels by using the Crushing Pin-on-Disc device. This device is based on the common pin-on-disc principle with the addition of abrasives as loose particles between the pin and the disc. The wear resistant steel specimens were first subjected to a running-in period. One set of specimens was run-in with quartz and the other set with granite. After all the specimens were tested with granite; the specimens with quartz running-in suffered less wear than the specimens that had been run-in with granite. The reason for this was that quartz had formed an in-situ composite on the surface of the steel specimens during the running-in period. This composite layer is thin but hard and it effectively resists granite abrasive penetration into the surface and thus reduces the wear rate.

View full abstract

In this research, dynamic friction behavior of paper-based wet friction material subjected to contact pressure fluctuation was investigated experimentally and theoretically. Complex friction coefficient obtained by the ratio between dynamic components of friction and normal force was defined as an index of dynamic friction characteristics. First, the frequency dependence of complex friction coefficient was measured changing the contact surface dimension and compressive modulus of specimen as parameters. As a result the amplitude and phase angle of complex friction coefficient decreased with the increase of pressure fluctuating frequency and this tendency was significant for larger dimension and for lower modulus. Then, calculations were done combining the stress-strain analysis with an analytical model based on the theory of poroelasticity and the assumption in which the solid part at contact surface only contributed to friction. It was found that the increase in load sharing ratio by fluid caused by the flow resistance made the solid contact relaxed and delayed, which resulted in the decrease in amplitude and phase angle of complex friction coefficient. The calculated results showed similar tendency to the experimental ones, thereby the analytical model was appropriate and the mechanism of dynamic friction behavior of paper-based wet friction material was demonstrated.

View full abstract

Plastic parts such as syringe, phone cases, containers, etc. are formed in the mold under the molten temperature and with the high pressure. Plastic sticking to the mold surface during forming process is a serious practical problem for the manufacturing. The sticking limits mold lifetime, reduces production speed and degrades product surface quality. Mold material, surface condition, plastic chemical properties and molding parameters effect on the sticking. In this work, the effectiveness of surface treatments including mechanical polishing, plasma nitriding, hard DLC coating and TiB₂ ion implantation were investigated in regards to reducing the plastic sticking on the steels - SKD61, HPM38 and PX5 surface. The surface finishing was characterized with surface roughness, hardness, friction coefficients and wettability. Adhesion strength of the steel - plastic interface for the plastic materials: polypropylene (PP), polystyrene (PS), polyethylene terephthalate (PET), poly-butylene terephthalate (PBT) were measured with the developed method, with the concept of real surface area. It was shown that, for the different plastics, the appropriate die material and die finishing must be chosen to provide the lowest plastic sticking.

View full abstract

Hydrogen-free carbon films were synthesized by a high density plasma assisted sputtering source (HiPASS). In the HiPASS a high density (> 10¹² cm^-3) remote Ar plasma was used to sputter a graphite cathode. As a direct current sputtering voltage was changed from -400 to -800 V the deposition rate was linearly increased from 3.5 to 8 nm/min. Raman spectroscopy showed that the ratio of D- and G-peaks (I(D)/I(G)) was increased 0.89 to 1.68 and the position of G-peak was shifted from 1573.8 to 1575.1 cm^-1 as the sputtering voltage is negatively increased. This corresponds to the phase transition from amorphous carbon to nano-crystalline graphite with the decrease of sp³ fraction, which causes the decreases of nano hardness from 23 to 22 GPa. In an asymmetric pulsed sputtering with fixed voltage (V_p-p = -600 V), the ratio of I(D)/I(G) was increased 1.10 to 1.41 as a positive duty is increased from 0 to 14%. The electron heating of graphite target during a positive duty increased the target temperature, resulting in the formation of sp² dominant carbon film and the decreases of nano hardness from 22 to 21 GPa.

View full abstract