Irradiation of ultrashort laser pulses with energy intensity near processing threshold can create fine periodic structures. High-speed forming of more than one million ripples per second can be achieved by scanning irradiation with a single laser light path. Laser texturing adopting the periodic structures has a wide variety of surface functions. This article describes forming principles of the periodic structures, and surface functions of the structures related to tribological characteristics such as friction/wear reduction and wettability control.
Whirling Electrical Discharge Texturing (WEDT) was developed to process microstructures on the inner surface of cylindrical parts and texturing characteristics were investigated. Then, a novel method of WEDT using a straight wire tool electrode for a cylindrical surfaces with a small diameter and a new EDT equipment with a feeding, guiding and bending system for a wire tool electrode was developed. It was confirmed that microstructures could be created on the inner surface of a cylinder of Φ 1.1 mm diameter, and that the texture-area ratio could be controlled by the workpiece feed speed. Moreover, a new WEDT device was developed to create microstructures on the surface of disc workpiece for the ball-on-disc or the pin-on-disc friction test. It was confirmed that the textured surface creating by WEDT was effective for reducing friction coefficient and the optimal texture-area ratio exists according to the lubrication conditions.
Electrolyte jet machining (EJM), one of the electrochemical processes, can be used for fabricating micro patterns on curved surfaces and surface texturing. In EJM, a workpiece is machined only in the area hit by the electrolyte jet which is ejected from a nozzle. Micro indents formed by EJM on rolling bearing surfaces showed higher capability of oil film formation, increasing the rolling contact fatigue life. Depending on the current density, the surface integrity can be changed from mirror-like surface to rough surface. One of the applications of the roughened surface is to realize direct bonding at the interface between metal and polymer.
It is known that metal nano dot arrays, which comprise metal particles of submicron size aligned on a surface of glass, exhibit unique optical characteristics due to LSPR (Localized surface plasmon resonance). These characteristics are expected to be applied to biomolecular sensors and SERS (Surface Enhanced Raman Spectroscopy). Efficient manufacturing process of metal nanodot arrays has been developed by using self-organization. This paper introduces these processes these processes and prospects of this technology.
Photonic nanojet (PNJ) is a high intensity light beam generated from a dielectric microsphere illuminated by a laser light. The beam diameter of a PNJ is several hundred nanometers, which is smaller than that of a focused laser beam with a high numerical aperture. A PNJ can propagate longer than 1µm while maintaining a smaller beam diameter than 1µm and a high intensity with little divergence. PNJ has different characteristics from the conventional focused laser beam. These properties of PNJ enable three-dimensional laser micro machining. By controlling the position and the intensity distribution of a PNJ, the processed feature size can be controlled in nanometer scale. Machined holes with the diameter of sub-micrometer scale can be obtain even when the PNJ was defocused by 0.5µm. Control of the intensity distribution of PNJ by incident wavelength enables high resolution control of the hole diameter in nanometer scale. PNJ is suitable for three-dimensional laser micro machining in nanometer scale.
Friction modifiers (FMs) are added to lubricating oils to reduce friction. For severe sliding, reaction film FMs (RF FMs) reduce friction, while adsorption film ashless FMs (AF FMs) do not reduce it. However, for mild sliding, AF FMs reduce friction, while RF FMs do not reduce it. From these perspectives, many studies have been conducted concerning the combined system to cover a wide lubrication range. According to past studies, it was shown that the RF of MoDTC (MoS2) promotes absorption of ashless FMs. Therefore, if the adsorption force of an ashless FM on the metal surface and the reaction film could be measured, it would help to improve the tribological properties of the lubricating oil. In this study, the adsorption forces on mica, platinum, and copper are measured in non-polar hydrocarbon solvent using colloid probes that are chemically modified with either COOH or CH3. Consequently, the adsorption forces on mica and copper as measured with the COOH probe are larger than those measured with the CH3 probe. These results suggest that adsorption forces can be measured with colloid probes, and they show the possibility of distinguishing between chemical and physical adsorption.
Boron doped tetrahedral amorphous carbon (ta-C:B) coatings were deposited with Filtered Cathodic Vacuum Arc (FCVA) method using boron doped graphite target (B=0, 5 and 10 at. %). The material properties and tribological properties of ta-C:B coatings were obtained at 23~300℃. The amount of boron contents in ta-C:B coatings are from 0 to 5.1 at. %, and the hardness of coatings ware more than 30 GPa. The friction coefficient of ta-C:B3.1 at 300℃ is about 0.02 in air. The specific wear rate of ta-C:B coating were lower than normal ta-C coating by 34% and 46% for ta-C:B3.1 and ta-C:B5.1, respectively. The sp2/(sp2+ sp3) ratio measured by XPS and O/C ratio measured by AES increased through the friction at 300℃ for ta-C, on the other hand both values did not change for ta-C:B. Friction coefficients of ta-C:B3.1 were shown as 0.055 at 23℃ and about 0.02 at 100~300℃. The specific wear rate of ta-C:B3.1 at 23~300℃ in air was about 2.0 × 10−6 mm3/Nm. From these results, we confirmed that ta-C:B shows lower friction and higher specific wear resistance at 23~300℃ in air than ta-C.
A linear equation of viscosity-pressure-temperature-density of lubricants was derived in the former report (1st part), and a linear equation of density-pressure-temperature was derived in 2nd part. If the gradients δ [K/GPa], a [GPa・K] and intercept b [‒] of the respective linear equations are found, it is possible to easily calculate the high pressure viscosity, the high pressure density and the pressure viscosity coefficient. In this report, author investigated whether these three values can be predicted by multiple regression analysis with the molecular structure of lubricant independent of pressure as an explanatory variable. As a result, attention was focused on the molecular weight and the functional group of the molecular structure showing the properties of the lubricant. Each atom as the minimum unit of the segment, that is, primary to quaternary carbon, aromatic carbon, carbonyl carbon, carbonyl oxygen and ether oxygen atoms, or hydrogen atoms bonded to primary to tertiary carbon were used as explanatory variables. Further, each density and viscosity at 40℃ and 100℃, which can be measured at atmospheric pressure, and refractive index,viscosity index, the temperatures at density of 0.75g/cm3 and 0.95g/cm3, furthermore, temperature at viscosity of 107mm2/s were used as explanatory variables. Author derived each multiple regression equation using these explanatory variables.
This paper describes the boundary lubrication property in the lubricant containing molybdenum phosphate (MoP) and zinc dialkyldithiophosphate (ZnDTP). To study this, spinning type friction test was conducted, and the chemical reaction film formed after the test was analyzed by energy-dispersive X-ray analysis and Raman spectroscopy. The results showed that the friction coefficient in the combined condition of MoP and ZnDTP was lower than that in the condition using molybdenum dithiocarbamate. In addition, surface analysis results revealed that the chemical reaction film comprising molybdenum disulfide, phosphorus film and sulfide film was formed on the friction surface after the test, with formed molybdenum disulfide showed the layer film structure. It was also shown that the friction coefficient depends on the concentration of ZnDTP, with the condition of sulfur concentration of 300 ppm having the lowest coefficient in this test conditions. Moreover, the concentration of sulfur in the chemical reaction film increased with increasing the concentration of ZnDTP, that implies the friction properties relates with the amount of sulfide film such as iron sulfide.