Diamond-like carbon (DLC) is widely used as a hard, protective layer with a relatively low surface energy. In the head‒disk interface in magnetic disk drives, however, the DLC layer is coated with a monolayer perfluoropolyether lubricant with a high bond ratio to avoid DLC‒DLC contact and to secure head/disk wear reliability. In this study, we theoretically analyzed the effect of lubricant thickness and bond ratio on the adhesion force between the head‒disk interface (HDI) in a mono/submono-layer thickness regime. It was found that the adhesion force had the lowest sensitivity to lubricant thickness variations at a 0.85 bond ratio. In addition, the maximum adhesion force was minimized when the lubricant thickness was ~0.6 nm for the measured parameter values of the HDI. This suggests that the current lubricant thickness of 1.0–1.2 nm can be reduced to 0.6 nm, accompanied by a slight decrease in the adhesion force and a slight increase in the resistance against any variation in its thickness. This tribo-surface-modification concept can be applied to surface-modification coatings in other fields such as micro/nano-electromechanical systems. The compatibility of the theoretical surface energy function with experimental data indicates the validity and consistency of this theory.
The lotus and taro leaf surfaces are superhydrophobic. We fabricated different surface patterns of lotus and taro leaves on Si surfaces and compared their contact angles and tribological properties. Three types of lotus patterns, consisting of a simple dot matrix of circular pillars with different pitches, and six types of taro patterns having the pillars distributed within a field of hexagonal ridges with different central pillar diameters and pitches, were prepared. The contact angles of water and hexadecane on these patterns were measured, and the wear resistance of each pattern was evaluated by reciprocating wear tests. The taro pattern showed a significantly higher contact angle for hexadecane and a lower coefficient of friction than the lotus pattern. The taro pattern ridges are supposed to contain air in the valleys between the ridges and pillars, which prevented sticking between the pillars and cloth fibers. Thus, the taro pattern exhibits better oleophobicity and a lower frictional force.
The aim of this study is to investigate the effect of plasma nitriding pre-treatment on hardness and tribological behavior of the hard coatings produced by Physical Vapor Deposition (PVD). AISI 316L austenitic stainless steel were subjected to surface modifications by plasma nitriding. W-Cr-Ti-Al-N coatings were prepared by multi-arc ion plating equipment in a modified commercial system. The surface morphology and microstructure analysis showed that a duplex surface layer structure consisting of the 2.4 µm W-Cr-Ti-Al-N coating with supported by nitrogen expanded austenite phase and CrN precipitation + ferrite phase diffusion case was generated by the plasma nitriding. The reciprocating friction tests were performed against bearing steel counterparts on a UMT-3 tribometer at room temperature. The friction and wear tests demonstrated that the difference of hardness between the hybrid specimens and those only nitrided specimens, and the former specimens showed a significant amount of wear resistance with decrease in the coefficient of friction in comparison to the latter ones.
To enhance tribological contacts under cyclic load, high performance materials are required. Utilizing the same high-strength material for the whole machine element is not resource-efficient. In order to manufacture machine elements with extended functionality and specific properties, a combination of different materials can be used in a single component for a more efficient material utilization. By combining different joining techniques with subsequent forming, multi-material or tailored components can be manufactured. To reduce material costs and energy consumption during the component service life, a less expensive lightweight material should be used for regions remote from the highly stressed zones. The scope is not only to obtain the desired shape and dimensions for the finishing process, but also to improve properties like the bond strength between different materials and the microscopic structure of the material. The multi-material approach can be applied to all components requiring different properties in separate component regions such as shafts, bearings or bushes. The current study exemplarily presents the process route for the production of an axial bearing washer by means of tailored forming technology. The bearing washers were chosen to fit axial roller bearings (type 81212). The manufacturing process starts with the laser wire cladding of a hard facing made of martensitic chromium silicon steel (1.4718) on a base substrate of S235 (1.0038) steel. Subsequently, the bearing washers are forged. After finishing, the surfaces of the bearing washers were tested in thrust bearings on an FE-8 test rig. The operational test of the bearings consists in a run-in phase at 250 rpm. A bearing failure is determined by a condition monitoring system. Before and after this, the bearings were inspected by optical and ultrasonic microscopy in order to examine whether the bond of the coat is resistant against rolling contact fatigue. The feasibility of the approach could be proven by endurance test. The joining zone was able to withstand the rolling contact stresses and the bearing failed due to material-induced fatigue with high cycle stability.
This article aims to experimentally study a slipping thin film on a roller of varying configurations. The investigated options include a smooth roller, a roller with a v-grooved surface, and a roller with holes under varying web tension and air temperature. The slippage phenomenon is a serious problem in the manufacturing of thin films, because it prevents continuous production and associated costs will increase. Therefore, the roller should be modified in order to mitigate the effects of slippage. To study the modified roller surface , an experimental apparatus was designed. The driving roller was modified to add holes, and an acrylic chamber covered the experimental apparatus to control air temperature. The specific web examined in this study was Polyethylene terephthalate (PET). The experiment showed that the roller with holes is an effective alternative for reducing slippage of web. The air temperature also greatly affected slippage of the web. When the air temperature increased above the ambient temperature of 60 degrees celsius, the operating web speed needed to be decreased in order to eliminate slipping.
This research focuses on the optimum design of fluid dynamic bearing (FDB) named modified spiral design. The objective is to improve the pressure and velocity distribution inside the FDB. In this paper, the current spiral design has 12 number of grooves while the modified spiral design has 24 number of grooves. Both design can be classified into two, bearing with seal and without seal. Air was chosen to replace the oil as the lubricant. Results show that the modified spiral bearing design has comparable characteristics compared to conventional spiral design in terms of pressure and velocity distribution. Modified spiral geometries also shows a tendency to replace the function of seals in FDB. This makes it possible to simplify bearing design without using any seal just by modifying its geometries based on novel modified spiral geometries. Experimental verifications also proved that the modified spiral bearing design has better air leakage control compared to the conventional ones. This phenomenon occurs in both design parameters, where when the designs are compared with respect to increase of rotational speed and air film thickness.
A lubricant is a substance introduced between surfaces in mutual contact to reduce friction, which ultimately reduces the heat generated when the surfaces move. Liquid lubricant, designed specifically for metalworking processes, such as turning, drilling, milling etc. is known as cutting fluids (CF). Cutting fluid is a blend or combination of oil, emulsifier and additives, mostly derived from chemicals or petroleum products. However, it has got many side effects as it is toxic and harmful to environment during its disposal. Hence, vegetable based cutting fluid or green cutting fluid (GCF) is being developed and gaining importance with time. Properties of these cutting fluids are dependent on the nature of the base-oil, nature of surfactants and the properties of water used to make the CF. These fluids act on the nascent surfaces generated during cutting to form a low friction boundary layer as they slide past the cutting tool. We propose a unique tool-chip tribometer (TCT) in which these boundary layers, formed by the action of lubricants on freshly cut surfaces, can be generated and their tribological properties alone studied in isolation. This equipment can be used to study the fundamental mechanisms of the lubrication using emulsions on nascent surfaces and can be used in optimizing the composition of such fluids. The scope of this work is to assess different cutting fluids in this tool-chip tribometer. The tribological performances of metal cutting on nascent surfaces are compared. Unlike in the conventional methods of assessing the lubricity of cutting fluids using cutting tests, here the friction has been evaluated separately from cutting forces.