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The present study reports on the systematic analysis of the friction and the wear behaviors of carbon nitride (CNx) thin films deposited by direct current unbalanced magnetron sputtering. We focus on the normal load dependence on the friction coefficient and wear rate for the sliding friction of the SUJ2 ball with the CNx thin film. The friction coefficient was monitored using a ball-on-disc apparatus with various loads in ambient air. The friction coefficient (μ) increases linearly from ∼0.05 to 0.28 with increasing normal load, while the specific wear rate decreases with an increase in load. The wear rates of the SUJ2 ball ∼1.5 × 10−7 mm3/Nm for μ = 0.05 and ∼5.5 × 10−8 mm3/Nm for μ = 0.28 were observed in the deposited CNx films with the minimum and maximum normal load. The friction and wear mechanisms are discussed in relation to the surface morphology and microstructure of the CNx coatings.

Investigations on tribological behaviors of Diamond-like Carbon (DLC) coating against other materials are strongly needed for scientific and industrial purposes. Recently, carbon diffusion has been found to play a key role in the wear of hydrogenated amorphous carbon (a-C:H) DLC coating when it is rubbed against steel counterpart material in boundary lubrication. Chromium has been reported to decrease carbon diffusion due to increase of the activation energy. In this research, we investigated on the effects of carbon diffusion on friction and wear properties of a-C:H coating when rubbed against Cr plating material. Results show that compared to steel counterpart, a-C:H coating exhibits lower friction coefficient, lower wear rate, and lower carbon diffusion rate when rubbed against Cr plating counterpart.

In this study, wear behavior of amorphous hydrogenated carbon (a-C:H) coating and tetrahedral amorphous carbon (ta-C) coating when sliding against various mating materials in base oil boundary lubrication condition is comparatively investigated to find out the optimal combinations of DLC/mating material and corresponding wear mechanism of both DLC coating. Tribological tests were performed in a cylinder-on-disc tribometer, Field Emission Scanning Electron Microscopy, Raman spectroscopy is used for characterization of ta-C and a-C:H worn surface. The results show that the specific wear rate of ta-C coating increases along with the hardness and roughness of mating material increases, while the specific wear rate of a-C:H coating increases together with an increment in the ID/IG ratio. It is concluded that for ta-C coating, local stress concentration-induced microfracture is the main wear mechanism in relative high wear scenario, along with minor graphitization-induced wear which prevails in low wear scenario. On the other hand, a-C:H coating showed that simultaneous generation and removal of the graphitized layer on the contact surface is the predominant wear mechanism.

Wear of DLC coating has been great concern in DLC/Steel sliding surface lubricated by molybdenum dithiocarbamate (MoDTC) containing lubricants. However, in order to design lubrication system with DLC and MoDTC, the mechanism of this issue is needed to be clarified. In this study, the roller-on-disc oscillation friction test by SRV friction tester was conducted to provide the hypothesis about the mechanism of wear of DLC with MoDTC. In friction test, DLC coatings (a-C:H and ta-C) were coated on discs. Counterpart was the SUJ2 bearing steel roller. It was found that MoDTC in lubricants accelerated the wear of the both two DLC coatings and it was dramatic especially for a-C:H coating. In order to clarify the enhancement mechanism of MoDTC for wear of DLC coatings, the surface analysis on DLC coatings and steel roller was conducted with XPS (X-ray Photoelectron Spectroscopy) and surface profile meter. As a result, sp2 ratio increased layer was observed on the a-C:H coating with XPS and the surface roughness of wear track was larger than out of wear track after sliding with MoDTC containing lubricant. On the other hand, ta-C did not show the increasing of sp2 ratio and the surface roughness of wear track decreased after sliding with and without MoDTC containing lubricant. For both DLC coatings, tribofilm generated from MoDTC was also observed on the counter SUJ2 roller surface with XPS. Depth profile of chemical elements of the tribofilm on the steel roller with XPS contributed to clarify the distribution of Molybdenum compound as MoO3 and Mo2C. Top surface was MoO3 and the interface between the SUJ2 roller and tribfilm was Mo2C. The authors provide the hypothetical model about a tribo-chemical reaction between both DLC coatings as ta-C or a-C:H and tribofilm from MoDTC.

This work shows new method which controls adhesion strength between acrylic resin and metal mold with electric field. Usage of electric field is considered as a new solution to control adhesion of thermoplastic resin in Carbon-Fiber-Reinforced ThermoPlastic (thermoplastic CFRP) stamping process because this method can prevent CFRP from its degradation. In this work, we establish new adhesion tester which can apply Direct Current (DC) or Alternating Current (AC) field on metal specimens. In the results, when DC −12 V/mm is imposed on metal specimens, adhesion strength increases to 0.81 MPa which is 57% higher than that of no field condition. Negative component of surface energy after imposing DC −12 V/mm on metal specimens is 7.6 mJ/m2. This value is 56% smaller than that of no field condition. When AC electric fields is imposed, adhesion strength decreases from no electric field condition. The most effective AC field condition is AC 10 V/mm with 1 MHz, in which case adhesion strength is 0.29 MPa. This value is 44% lower than that of no field condition.

The wear mechanism of diamond-like carbon (DLC) in hot, pressurized water has been studied by the oxygen depth profile of DLC films pre and post a sliding test. The sliding test between DLC films coated on chromium molybdenum steel (JIS SCM420) pins and austenitic stainless steel (JIS SUS316) plates was conducted in a water environment by using high temperatures of 100, 200, 250 and 300°C and a high-pressured (10 MPa) autoclave friction tester. The dissolved oxygen concentration (DO) was 0.52 mg/L for oxygen-poor water and 40 mg/L for oxygen-rich water. The experimental results showed that the specific wear rate of DLC was strongly related to the water temperature and the DO concentration. The specific wear rate in both cases of oxygen-poor and oxygen-rich water showed a temperature dependency. When the temperature was below 200°C, the specific wear rate of DLC did not depend on the DO concentration. On the other hand, when the water temperature was more than 200°C, the specific wear rate drastically increased with the DO concentration. In order to prove the effect of oxidation on the wear rate of DLC, the depth profile of the oxygen concentration was compared to that of the carbon concentration on the inside and outside of the wear scar of DLC after sliding tests in hot, pressurized water. When the concentration of DO in the water was low at 0.52 mg/L, the O/C ratio was not affected by the water temperature. On the other hand, when the concentration of DO in water was high at 40 mg/L, the O/C ratio of the top surface increased from 0.05 to 0.18 with an increase in the water temperature on the inside of the wear scar of DLC, where the O/C ratio on the inside of the wear scar was higher than that on the outside of the scar. On the basis of the estimated rate of reaction between DLC and oxygen, determined from a linear relationship between ln (Oxidation wear volume) and the inverse temperature, it was concluded that the oxidation of DLC governed the wear of DLC in hot, pressurized water. Friction was found to enhance the oxidation wear of DLC from the estimated activation energy.

Long Fiber Thermoplastic-Direct (LFT-D), a new stamping method, has been developed to achieve the short cycle-time manufacturing of Carbon-Fiber-Reinforced thermoplastics (thermoplastic CFRP). In LFT-D method, to shorten cooling time is one of the effective way for achieving more productive manufacturing. During ejection sequence in the LFT-D, thermoplastic resin parts adhere stronger than previous method. High adhesion affects smoothness of the component surface, cycle-time and requested specifications of equipment. So, it is required to reduce the adhesion between the metal mold and thermoplastic resin. This paper reports the effect of nano-texturing on adhesion of thermoplastic resin against the textured steel around glassy-transition temperature. Experimental results show that the adhesion strength increases proportionally with the ratio of contact area. The lowest adhesion strength on nano-textured surface is 0.18 MPa, which is 66% lower than that of flat surface. It is clarified that surface adhesion energy increases with the ratio of contact area Acontact to circumference of contact area Lcircumference.

ZnDTP antiwear additive for lubricating oil is known to absorb strongly on sliding surfaces in boundary lubricated tribosystems, forming a tribofilm, which is able to reduce the wear of involved surfaces. It is also known to increase the friction coefficient in most DLC/DLC contacts, with the exception of ta-C DLC / ta-C DLC contact, for which the difference in friction behaviors between a base oil + ZnDTP additive lubricated tribosystem and a base oil lubricated tribosystem is not very significant. In this study we investigate a characterization method of the shape of the tribofilm formed on different types of DLC coatings and on the relation between the shape of the tribofilm and the friction behavior of the related DLC coating. Results show that compared to other investigated DLC types, the tribofilm formed on ta-C DLC has some unique characteristic topography features that promote lower friction coefficient.

This paper addresses a novel lightweight and low starting torque bearing with looped carbon fiber brush (LCFB). LCFB simulates bristle of living being. Moreover, the static friction coefficient is nearly equal to the kinetic friction coefficient. By applying LCFB to a slide bearings, where a shaft is supported by multiple LCFBs, it is realized low starting torque bearings as well as lightness compared to conventional ball bearings. In this paper, we manufacture prototype LCFB slide bearings. With the bearings, we compare friction torque between LCFB slide bearings, slide bearings and deep groove ball bearings. As results, the ratio of starting torque to regular torque of LCFB slide bearing is from 0.93 to 1.07 which is smaller than that of the slide bearing. When micro-spline shaft is used as a mating material of LCFB slide bearing, the torque reduces because of decrease of real contact area between LCFB and mating materials. In addition, since LCFB utilize elastic deformation of fibers, LCFB slide bearings are not endurable in heavy radial load as high as load rating of ball bearing. Therefore, we define the load capacity of LCFB slide bearing from buckling load of a carbon fiber bundle to avoid overload state. We propose the load capacity as a design guideline of LCFB slide bearings.

This paper describes about the effect of drill surface texturing on height of back burr in titanium alloy drilling process with solid lubricating sheet. Titanium alloy is difficult to conduct drilling because titanium alloy is hard and ductile material. And the workers cannot use plenty of liquid coolant for preventing the productivity decline when the work places are above their heads in production fields. Therefore drills are exchanged frequently even though the cost increases. In this study, we measured the cutting force by a loadcell to know the effect of drill surface texturing and solid lubricating sheet on drilling process of work pieces made of Ti-6Al-4V. As the results, drill with rough textured rake surface showed high burr height in exit of Ti-6Al-4V. On the other hand, drill with rough textured flank surface showed low burr height only if drilling with solid lubricating sheet. Moreover, drill with the specific texturing on flank surface by wire electric discharge machining showed low burr height.

In this study, amorphous hydrogenated carbon (a-C:H) and Si-doped diamond-like carbon (Si-DLC) films were prepared using microwave sheath voltage combination plasma (MVP) deposition. The thermal stability of the a-C:H and Si-DLC films were investigated by performing an annealing test (100-700°C) in ambient air. Furthermore, the in situ high-temperature tribological properties on the films were investigated by performing a sliding test against a Si3N4 ball at high temperatures (100, 200, and 300°C). Hardness measurements and a tribological test showed that Si-DLC has better thermal stability than a-C:H; however, Si-DLC has a higher friction coefficient and undergoes more wear than does a-C:H in the in situ high-temperature tribological test. Therefore, the failure of Si-DLC is due to adhesive wear, whereas that of a-C:H is due to abrasive wear.

There is an issue of the fish adhering to the metal grids of grill strongly after grilling fish. Recently, the temperature in a grill equipment is over 500 °C, Fluorine resin coating which has low adhesion property can not endurant at 500 °C. In order to overcome this issue, we proposed a new grill not to adhere a fish with Ultra-Hydrophobic Diamond-like Carbon coating named as UH-DLC coating. UH-DLC coating has high hydrophobicity. We expected this coating to decrease wettability of water including fish protein and contact area, because fish protein includes about 90% water. Contact angle of water on UH-DLC was over 120° at room temperature. After heating at 500 °C for 54 minutes, UH-DLC kept ultra-hydrophobic property. On the other hand, Fluorine resin coating desappeared hydrophobic properties after heating at 500 °C for 54 minutes. It was conducted adhesion test for UH-DLC coating, Fluorine resin coating and no coating grilling rods after the grilling of real fish in a grill equipment by gas. The adhesion force between UH-DLC coating grill rods and real fish was as half as that of no coating grill rods and as much as that of Fluorine resin grill rods. So, we believe that Ultra Hydrophobic Diamond-like Carbon coating has a possibility for the usage as new grilling grids at high temperature.

Superhydrophobic double roughening structure of DLC film was prepared by 2.45 GHz surface wave-excited plasma CVD with the mixture of methane (CH4) and tetramethylsilane (TMS: Si(CH3)4) gases on the undulated DLC film by a series of plasma Ar etching, coating process and plasma Ar etching. Static wetting angle of water was observed that double roughening structure of DLC was superhydrophobicity such as wetting angle 161°. This approach also increased in air pockets easily trap among the needle-like posts. For the low friction at nanoscale, the surface wettability of the solid lubrication played a significant role, when the DLC film modified from flat to double roughening structure, the friction was constantly inner humidity conditions. Results generally showed that humidity had insignificant effect on the nanoscale friction at superhydrophobic DLC surface. The effect of the superhydrophobic double roughening DLC and friction were discussed with the following factors; the surface morphology affinity to needle-like shape, a reduction of the real area of contact, graphitization and easily occur to slip at small contact interface due to superhydrophobicity.

The adhesion force between a chloride-isobutene-isoprene rubber (CIIR) and stainless steel ball was studied in this paper. In order to decrease the adhesion force, the CIIR rubber was treated with high-density microwave plasma employing oxygen and argon gases. The experimental results showed that the adhesion force decreases with increasing treatment time and microwave power following both oxygen and argon plasma treatments. In addition, optical measurements revealed that the real contact area between a CIIR rubber and quartz plate decreases with decreasing adhesion force. The decreasing trend of the contact area was almost similar to that of the adhesion forces. The field emission scanning electron microscope image showed that the surface roughness generally increases with treatment time and microwave power, implying that roughening of rubber surface by plasma treatment is one of the reasons for the decrease in the adhesion force.

This paper clarified the effects of solid lubricating sheet for reduction of burr generation and lowering of cutting temperature through examining of drilling in titanium alloy for aircraft. Titanium alloy is difficult to drilling. Moreover worker cannot use plenty of lubricating oil in drilling. So drills are exchanged frequently even if the cost increases. In this study, the temperature of work pieces made of Ti-6Al-4V were measured by thermo camera while drilling. As the results, a height of back burr increases rapidly around 350～400℃ and more. Moreover, in specific range, the solid lubricating sheet can be decreased height of back burr and lowering of cutting temperature compared to without it.

In recent decades, different types of plasma sources have been used for various types of plasma processing, such as, etching and thin film deposition. The critical parameter for effective plasma processing is high plasma density. One type of high density plasma source is Microwave sheath-Voltage combination Plasma (MVP). In the present investigation, a better design of MVP source is reported, in which over-dense plasma is generated for low input microwave powers. The results indicate that the length of plasma column increases significantly with increase in input microwave power.

This paper clarified the effect of mold temperature affecting adhesion of thermoplastic resins which will be used in Carbon-Fiber-Reinforced Thermo-Plastic (Thermoplastic CFRP). CFRP which has high mechanical strength and lightness attracts considerable attention because of its possibility improving fuel economy. Many vehicle companies are developing new press molding method using Thermoplastic CFRP for achieving high productivity compared to Thermosetting CFRP which is used conventionally. One of the most important factors during press molding is mold temperature which affects adhesion between thermoplastic resins and mold surface. It is important to estimate the adhesion because strong adhesion causes long cycle time and poor surface quality. Adhesion tests were carried out at several mold temperature. Maximum adhesion strength of amorphous resins which consisted of Acrylic resin, Polycarbonate and Polyvinyl chloride were gotten around 126 degree Celsius, 163 degree Celsius and 82 degree Celsius, respectively. Maximum adhesion strength of crystalline resins which consisted of Polyamide 6, Polyamide 66 and Polypropylene were observed around 210 degree Celsius, 236 degree Celsius and 167 degree Celsius, respectively. We clarified amorphous and crystalline thermoplastic resins showed maximum adhesion strength around glassy transition temperature and melting point from the result organized by temperature index which is calculated from dividing mold temperature by glassy transition temperature and melting point, respectively.

Amorphous Carbon Nitride (a-CNx) coating is an attractive material that satisfies both relatively high hardness and ultra-low friction coefficient. We have tried to obtain a-CNx by using plasma-enhanced chemical vapor deposition (PECVD), which is more suitable for 3-dimensional coating than typical physical vapor deposition methods. However, considering the application of a-CNx coatings for real machine parts, ultra-low friction property is expected to express under oil lubrication. Thus in this work, the friction characteristic under oil lubricated of Si-containing a-CNxHy films deposited by PECVD was evaluated especially by analyzing the relation between the Raman spectrum, which is a proper index of carbon structure, and the friction coefficient of the films. In particular, the relation between friction coefficient and ID/IG ratio from Raman spectroscopic analysis of Si-containing a-CNxHy films was focused on. The friction coefficient decreased with the increasing of ID/IG ratio in the range of 0.63-0.78, and the minimum low friction coefficient of 0.055 was shown for the ID/IG ratio of 0.78. However, even for a film with the ID/IG ratio of 0.32, similar low friction coefficient of 0.051 was shown. Moreover, for a film with the ID/IG ratio of 0.34, which is almost unchanged from 0.32, the increased friction coefficient of 0.105 was shown. In these films, the amount of hydrogen in Si-containing a-CNxHy film increased from 33% to 37%, which is considered to mainly cause the increased of friction from 0.051 to 0.105. Two more exceptions were seen for some films where the friction characteristic is not correlated with ID/IG ratio, but may be affected by maximum height roughness (Rz) and C=N combination. When maximum height roughness (Rz) was in the range of 203 nm-414 nm, transfer layer formed on counter material, and it showed lowest friction coefficient of 0.02. In addition, the friction coefficient was linearly decreased with the increase of C=N bond amount; the friction coefficient of 0.027 was achieved for the IC=N/IG ratio of 0.44.

Nowadays, high frictional and low aggressive disc brake is required. For designing it, we have had to depend on empirical way because brake pad is complicated composite. We therefore attempted to optimize abrasion caused by abrasive which is one of the most important containing materials in brake pad. However, in general abrasion, high friction cannot provide low aggressiveness. In order to overcome this issue, we focused on degree of wear fab which has an effect on the ratio of wear coefficient to friction coefficient K / μ. In our previous (1st) report, by conducting scratch test with using 4 types of abrasives (CFP, FFP, AP1 and AP2), we clarified the effect of abrasive shape (open angle φ) on degree of wear fab ; degree of wear fab increased with increasing open angle φ except in FFP. Then we proposed small open angle abrasive for high frictional and low aggressive disc brake. This report, we conducted scratch test with using 7 disc materials as counter-part: SUS304, FC200, Pure Al, Pure Cu, Ti-Al-V, Ni-Cr-Fe and Al-Mg-Mn. Then we confirmed that in all disc materials degree of wear fab increased with increasing open angle φ, which strengthened our 1st report and we clarified the effect of property of disc material (toughness W) on degree of wear fab ; degree of wear fab decreased with increasing toughness W. Thus we proposed small open angle abrasive and tough disc material for high frictional and low aggressive disc brake.

Disc brake is one of the most important auto mobile components and the toughest frictional components. Nowadays, the lightweight disc brake is needed for better fuel-efficient. To reduce the weight, high frictional and low aggressive brake pad is required. However, generally high friction cannot provide low wear of counter-part, therefore to make such brake pad is difficult. In addition, including many kinds of materials such as abrasive, binder, filler and so on, we cannot design it theoretically. In order to overcome these issues we focused on abrasive shape in brake pad, especially focused on open angle of abrasive φ and the important index “degree of wear fab”. If degree of wear fab decreases with open angle φ of abrasive and reduction of wear is more than reduction of friction, we can propose the high frictional and low aggressive brake pad which includes small open angle abrasive. In order to validate our proposals, we conducted the scratch test using Vickers indenter and Knoop indenter. As a result of the scratch test, we clarified that the ratio of wear coefficient to friction coefficient K / μ is correlated with degree of wear fab, and in the region of ploughing and wedge, degree of wear fab decreased with decreasing open angle φ. Due to these phenomena, the ratio of wear coefficient to friction coefficient K / μ decreased with decreasing open angle φ in the region of ploughing and wedge. Thus it was valid that small open angle abrasive provides high friction and low aggressiveness.