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Carbon nanotubes (CNTs) have a large specific surface area and, thus, are expected to have applications as electrodes, e.g., in fuel cells. A CNT-containing composite metal film with high electrode performance could be realized by implementing a large number of CNTs on the film. However, a composite film with a high density of CNTs has not yet been obtained. In the thermal spray field, including cold spray, metal–CNT composite films with more than 20 wt% of carbon nanotubes has not yet been deposited. In this study, high-density CNT-containing metal-based composite films were deposited onto an aluminum substrate by low-pressure cold spray from electroless nickel-plated CNT particles. The electroless nickel plating process caused slight structural damage to the CNTs, whereas the cold spray process did not cause any significant structural damage to the CNTs. Two phases were observed in the films: a CNT-rich layer and a nickel-rich layer. However, the CNTs maintained sufficient adhesive strength to remain attached to the bottom nickel phase. Composite films with at least 65 wt% CNT were produced with our method.

Diamond-like carbon (DLC) films have a high hardness and a low friction coefficient. Therefore, DLC films are applied in industrial fields to reduce energy consumption. However, DLC films can only be obtained as coatings, and DLC films of only micrometer thickness can be deposited on substrates. In this study, we focused on the cold spray (CS) technique as a means of obtaining a DLC-containing metal composite. DLC-containing metal composite films with a millimeter thickness and a low friction coefficient were obtained by depositing DLC-coated metal [copper (Cu) and titanium (Ti)] particles by the CS technique. For Cu particles, DLC-coated particles were prepared with two different deposition times. Then, composite films were fabricated by the CS technique using these particles. The thickness of the DLC-containing Cu(Cu-DLC) composite film was 200 μm and that of the DLC-containing Ti (Ti-DLC30) composite film was 252 μm, and the introduction of DLC into the metal films was demonstrated by Raman spectroscopy. Then, we conducted a sliding test using a ball to evaluate the sliding characteristic of each film. The Cu-DLC composite films deposited from thin DLC-coated Cu particles behaved as a solid lubricant in the ball-on-disk test and Cu-DLC composite films deposited from thick DLC-coated Cu particles acted as an abrasive. For Ti particles, DLC was graphitized and acted as an abrasive.

Sliding mechanical parts working under heavy loads and at high speeds in harsh environments are often subjected to sand and dust, leading to abnormal wear and seizing. Although sliding surfaces can be hardened and textured, there is a need for even higher wear and seizure resistance. We therefore did this study to confirm the trapping effect of surface texturing on dust by finding a way to visualize the dust. As a result, we confirmed that the dust became trapped in the grooves of the texture during the sliding. In addition, to produce a sliding surface having both seizure and wear resistance, we produced a surface combining a diamond-like carbon (DLC) film and surface texturing, and we evaluated its tribological characteristics. In dusty conditions, the specific wear rate was about 1/20 on surfaces where DLC film and the surface texturing were used in conjunction, and its wear resistance was higher than that of a non-treated stainless steel substrate. On the other hand, a rise in the coefficient of friction due to a rise in contact stress on the corners of the texturing grooves was confirmed. Therefore, when the tribological characteristics were evaluated by changing the radii of the groove corners and the parameters of the groove depth, the coefficient of friction was the lowest, decreasing about 50% for the test sample with a corner radius of 7.1 μm.

Hydrogenated amorphous carbon (a-C:H) films have optical and electrical properties that vary widely depending on deposition conditions, however, the electrical conduction mechanism, which is dependent on the film structure, has not yet been fully revealed. To understand the relationship between the film structure and electrical conduction mechanism, three types of a-C:H films were prepared and their film structures and electrical properties were evaluated. The sp2/(sp2 + sp3) ratios were measured by a near-edge X-ray absorption fine structure technique. From the conductivity–temperature relationship, variable-range hopping (VRH) conduction was shown to be the dominant conduction mechanism at low temperatures, and the electrical conduction mechanism changed at a transition temperature from VRH conduction to thermally activated band conduction. On the basis of structural analyses, a model of the microstructure of a-C:H that consists of sp2 and sp3-bonded carbon clusters, hydrogen atoms and dangling bonds was built. Furthermore, it is explained how several electrical conduction parameters are affected by the carrier transportation path among the clusters.

Amorphous boron carbon nitride (a-BCN) films exhibit excellent properties such as high hardness and high wear resistance. However, the correlation between the film structure and its mechanical properties is not fully understood. In this study, a-BCN films were prepared by an arc-sputtering hybrid process under various coating conditions, and the correlations between the film’s structure and mechanical properties were clarified. Glow discharge optical emission spectroscopy, X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, and Raman spectroscopy were used to analyze the structural properties and chemical composition. Nanoindentation and ball-on-disc tests were performed to evaluate the hardness and to estimate the friction coefficient and wear volume, respectively. The results indicated that the mechanical properties strongly depend on the carbon content in the film, it decreases significantly when the carbon content is &lt, 90%. On the other hand, by controlling the contents of boron and nitrogen to a very small amount (up to 2.5 at.%), it is possible to synthesize a film that has nearly the same hardness and friction coefficient as those of an amorphous carbon (a-C) film and better wear resistance than the a-C film.

In sliding parts used by construction machines which is operate in harsh environment, one of the problems is that abnormal wear and seizure occur due to sliding under dusty condition. That severe wear is caused by sand dust intervening on the sliding surface. In order to prevent severe wear and seizure, a combination of an iron-based material and a soft metallic material such as brass is used on the sliding surface. And more,, we applied DLC (diamond-like carbon) coating on the surface of soft metallic materials. Specifically, we deposited segment structured DLC film on copper alloy, and evaluated its tribological characteristics by reciprocating sliding test. As a result, segment structured DLC coatings on soft metallic material showed more than three fold high wear resistance and seizure resistance as compared with DLC coated SUS440C, when dust is mixed in lubricant.

Diamond-like carbon (DLC) films have excellent properties such as high hardness, low friction coefficient, high wear resistance, chemical inertness and so on. Because DLC film is considered as an effective coating material to improve their surface properties, this films are used in various applications such as parts for automobiles engines, hard disk surfaces, cutting tools and dies, and so on. DLC films consist of a mixture of sp2 bonded carbon atoms and sp3 bonded carbon atoms. Among them, ta-C film is known as the hardest and strongest film since it mainly consists of sp3 bonded carbon atoms. One of deposition methods to form ta-C is Filtered Cathodic Vacuum Arc (FCVA). The characteristic of this method is that it is possible to remove the droplets and form a high-quality film.. However, even though lots of mechanical components which require ta-C coating have three-dimensionally shapes, it is difficult to coat ta-C film three dimensionally by using FCVA process. At present, researches on 3D deposition of amorphous carbon films on three dimensional components is still insufficient, and investigation reports on the deposition mechanism and characterization of the deposited films are even more limited. In this study, we tried to deposit films on 3D components by the FCVA method and evaluated the microstructure and surface morphologies of films. Although films were coated successfully in the entire surfaces, different properties were showed depending on the location of components. These properties were investigated by Raman spectroscopy and laser microscope.

Graphene has been used to improve tribological property due to its extraordinary properties. For graphene composite, obtaining uniformly distributed and less damaged graphene is important for better improvement. In this research, graphene was fabricated on copper particle by thermal chemical vapor deposition to minimize structural damage and obtain uniform distribution. The obtained graphene-coated copper composite particle was deposited by cold spray which is less deteriorative for graphene. The scanning electron microscope images show that graphene appeared to surface of copper particle without any agglomeration. Raman spectrum indicates that mostly monolayer graphene was obtained. Uniform distribution of graphene was observed after the deposition by cold spray. Furthermore, the deposition by cold spray induced neglectable structural damages on graphene. Nevertheless 0.019 wt% of carbon corresponding to graphene was incorporated in the composite film, graphene improved tribological properties in comparison with those of the copper film; the average friction coefficient values were 0.60 and 0.46 for the copper and composite films, respectively, and the calculated specific wear rates of the films were 8.6 × 10−4 and 5.2 × 10−4 mm3/N∙m for the copper and graphene–copper composite films, respectively. The improved tribological properties resulted from the low shearing and passivation film by the incorporated graphene.

The graphitization process of a tetrahedral amorphous carbon (ta-C) film under lubrication was investigated using a laboratory-built in situ Raman tribometer. The coating was lubricated with poly-alpha-olefin (PAO), PAO with an added friction modifier (FM), glycerol mono-oleate (GMO). Friction tests were carried out using a ball-on-disk setup, in which a 19-mm diameter ta-C-coated ball was loaded and rubbed against a steel disk that was immersed in a lubricant solution. In situ optical microscopy and Raman spectroscopy were used to monitor the graphitization process and wear tracks of the ta-C-coated ball. Raman analysis was conducted on the rubbed surface of the rotating ta-C-coated ball when it was located under an objective lens every three minutes during sliding. In this study, the degree of graphitization of the ta-C surface was estimated by calculating the intensity ratio of the D-peak and G-peak (ID/IG) in the Raman spectra of the ta-C film during friction tests with different lubricants. All our results suggest that the friction modifier inhibits the progression of graphitization of DLC films by reducing friction, in other words, reducing the contact temperature, and the wear progression of DLC films under boundary lubrication can be induced by graphitization of DLC surfaces at the sliding contact.

The effects of the molecular structure of zinc dialkyldithiophosphates (ZDDPs) on the tribological properties of a hydrogenated amorphous carbon (a-C:H) film under boundary lubrication were investigated. Friction tests were performed at a-C:H/a-C:H and steel/steel contacts under lubrication with poly-alpha olefin (PAO) and PAO containing five types of ZDDPs with different alkyl groups (primary-C4 ZDDP, secondary-C4 ZDDP, primary-C6 ZDDP, primary-C8 ZDDP and primary-C12 ZDDP). All our results suggest that the structure of the alkyl chain of ZDDPs strongly influence the tribological properties of the a-C:H/a-C:H and steel/steel tribopairs lubricated with ZDDP solutions.

In this study, a precursor gas mixture of toluene and Ar was used for the deposition of a-C:H films on a trench (20-mm pitch and 10-mm depth), and the effect of the Ar flow ratio on the film properties was investigated. The a-C:H films were deposited using a bipolar-type plasma based ion implantation and deposition technique under a negative pulse voltage of − 2 kV. The mechanical properties of the prepared a-C:H films, including internal stress, hardness and adhesion strength, were measured by means of surface profilometry, nanoindentation and a microscratch test, respectively. Furthermore, the microstructure of a-C:H films was evaluated by Raman spectroscopy and Fourier transform infrared spectroscopy (FTIR). The results showed that the thickness uniformity across the trench surface is improved by the addition of Ar, in particular, at an Ar flow ratio of 80%. The film on the top and bottom surfaces of the trench tends to change from a PLC to DLC structure with increasing Ar flow ratio, resulting in a significant improvement of mechanical properties. In the case of the sidewall, the film tends to change to a more GLC structure with increasing Ar flow ratio due to the Ar+ ion bombardment and sputtering effect.

Ionic liquids (ILs) are expected to function as novel lubricants because of their superior properties compared to conventional lubricants. Although halogen-based ILs exhibit excellent tribological performance, they also cause corrosion of worn surfaces; thus, alternative ILs are required. To this end, cyano-based ILs have been investigated as functional lubricants that can reduce the environmental burden which other lubricants may cause. However, compared to conventional ILs, the tribological performance of cyano-based ILs was poor. However, their performance improved considerably when the chemistry of the sliding surface was changed. In addition, ultralow friction was obtained when the cyano-based ILs were used in conjunction with diamond-like carbon (DLC) films as the sliding surface. Overall, the results indicate that both the IL structure and the nature of the sliding materials must be carefully considered when cyano-based ILs are used as lubricants.

In order to improve the mechanical properties after thermal aging of an Sn–45Bi–2.6Zn (SBZ) alloy, which we had proposed in a previous study, in this study, we prepared Sn–Bi–Zn–In alloys and investigated the effects of the addition of In and Zn on their microstructure and mechanical properties before and after thermal aging. We found that the addition of In suppressed the microstructural coarsening of SBZ during thermal aging and can potentially help reduce the brittleness of Sn–Bi alloys. Moreover, the addition of In had significant effect on the elongation of SBZ. We theorized that the segregation of Zn at the Sn/Bi phase boundary and the formation of a solid solution of In in the Sn phase are responsible for this result. Thus, the investigated alloys have potential for use as lead-free solder materials in the electronics industry.

The role of the dynamic interactions between hydrogen in a solid solution and the stress-induced martensite transformation in hydrogen embrittlement has been investigated using trained Ni–Ti superelastic alloy. In a cyclic tensile test in the stress plateau region caused by stress-induced martensite and reverse transformations after hydrogen charging, a further decrease in the critical stress for the martensite transformation is observed. In addition, the number of cycles to fracture for a trained specimen is significantly larger than that for a non-trained specimen. Since most of the charged hydrogen is preferentially trapped in defects induced by training, the hydrogen embrittlement is considerably suppressed as a result of decreasing interactions between the hydrogen and the transformation. The present results indicate that hydrogen in a solid solution more strongly interacts with the stress-induced martensite transformation than hydrogen trapped in defects, thereby further enhancing the hydrog...

Hydrogenated amorphous carbon (a-C:H) films are only empirically known to be decomposed by heating, and this heat resistance is expected to be dependent on the structure of the film. To understand the decomposition processes and their uniformity, the thermal decomposition characteristics of two types of a-C:H film were investigated after the structural determination of the sp2/(sp2 + sp3) ratios and hydrogen contents. The mass of the gas released by thermal decomposition of the a-C:H films was detected by evaluation of the thermal desorption spectroscopy to determine the starting temperature the film with high hydrogen content started to desorb hydrogens at 400 °C and hydrocarbons at 750 °C. The film with low hydrogens started to desorb decomposition gases at 750 °C. Moreover, uniform decomposition of the films was observed using synchrotron-based X-ray photoemission electron microscopy (X-PEEM) and near edge X-ray absorption fine structure (NEXAFS) spectroscopy. The thermal decomposition of a-C:H films with uniform film structure proceeds relatively uniformly, and the mechanism of thermal decomposition of the films depends on the source materials of the films. The thermal decomposition proceeds uniformly at the micron scale when the initial structure is uniform.

Inhibition of the localized corrosion of Ni–Ti superelastic alloy in 0.9% NaCl solution has been attempted by charging with a small amount of hydrogen, which causes negligible hydrogen embrittlement. Upon a small amount of hydrogen charging, no pitting potential is observed in anodic polarization curves. From scanning electron microscope observations, localized corrosion is inhibited on the entire side surface of charged specimens. With increasing amount of charged hydrogen, the corrosion potential shifts in the less noble direction and the current density increases under anodic applied potential. When the hydrogen charged specimens are aged in the atmosphere at room temperature, the corrosion potential becomes almost the same as that of the non-charged specimen, but the inhibition of localized corrosion remains. The present study indicates that a small amount of hydrogen charging is effective for inhibiting the localized corrosion of the alloy in NaCl solution.

Hydrogenated amorphous carbon (a-C:H) films were deposited on a trench-shaped target (20-mm pitch and 10-mm depth) using a bipolar-type plasma-based ion implantation and deposition (bipolar PBIID the thickness and hardness of the a-C:H films on the sidewall of the trench were smaller and the film structure was more graphite-like than those on the top and bottom surfaces. Because the film properties of the a-C:H film are related to the incident energy per carbon atom, in this study, methane (CH4), which has a lighter mass and fewer carbon atoms (one carbon atom) in a molecule than toluene, was used as a precursor gas to enhance the incident energy per carbon atom and suppress the inertia in the vertical direction. The structure and mechanical properties of the a-C:H films were evaluated by Raman spectroscopy, XPS, AFM, and a nanoindentation test. In addition, a plasma simulation was conducted to determine the effect of the precursor gas on the ion and radical behavior and the coating mechanism. As a result, the use of the methane precursor gas leads to increasing the indentation hardness, to lowering the surface roughness, and to changing its structure from graphite-like to diamond-like as compared to the use of the toluene precursor gas.Hydrogenated amorphous carbon (a-C:H) films were deposited on a trench-shaped target (20-mm pitch and 10-mm depth) using a bipolar-type plasma-based ion implantation and deposition (bipolar PBIID the thickness and hardness of the a-C:H films on the sidewall of the trench were smaller and the film structure was more graphite-like than those on the top and bottom surfaces. Because the film properties of the a-C:H film are related to the incident energy per carbon atom, in this study, methane (CH4), which has a lighter mass and fewer carbon atoms (one carbon atom) in a molecule than toluene, was used as a precursor gas to enhance the incident energy per carbon atom and suppress the inertia in the vertical direction. The ...

Hydrogenated amorphous carbon (a-C:H) films were prepared on inner surface of 100-μm-width microchannel by using a bipolar-type plasma based ion implantation and deposition. The microchannel was fabricated using a silicon plate, and two kinds of microchannels were prepared, namely, with a bottom layer (open at one end) and without a bottom layer (open at both ends). The distribution of thickness and hardness of films was evaluated by SEM and nanoindentation measurements, respectively, and the microstructures of films were evaluated by Raman spectroscopy. Furthermore, the behavior of ions and radicals was analyzed simultaneously by combining the calculation methods of Particle-In-Cell/Monte Carlo Collision and Direct Simulation Monte Carlo to investigate the coating mechanism for the microchannel. It was found that the film thickness decreased as the depth of the coating position increased in the microchannels where it is open at one end. The uniformity of the film thickness improved by increasing the negative pulse voltage because ions can arrive at the deeper part of the microchannel. In addition, the hardness increased as the depth of the coating position increased. This is because the radicals do not arrive at the deeper part of the microchannel, and the incident proportion of ions relative to that of radicals increases, resulting in a high hardness due to the amorphization of the film. The opening area of the microchannel where the aspect ratio is very small, radicals dominate the incident flux, whereas ions prevail over radicals above an aspect ratio of about 7.5. On the other hand, in the microchannels that are open at both ends, there were great improvements in uniformity of the film thickness, hardness, and the film structure. The a-C:H films were successfully deposited on the entire inner surface of a microchannel with an aspect ratio of 20.

We observed the enhancement of fluorescence intensity due to the addition of GeO2 in bismuth-doped silica glass (BiSG), which has a peculiar fluorescence at 1.25 μm with a full width at half-maximum of 300 nm. Experimental results revealed that the fluorescence intensity from BiSG with 5.0 mol% GeO2 increased remarkably to be 26.3 times greater than that without GeO2 additive for the same Bi2O3 concentration (0.1 mol%). Furthermore, the enhanced sample showed almost the same intensity as BiSG without GeO2 for 1.0 mol% Bi2O3. These results demonstrate that GeO2 additive effectively promotes the generation of peculiar luminescent centers.

Recently, the bipolar-type plasma-based ion implantation and deposition (bipolar PBII&D) method has attracted large attention owing to its non-line-of-sight coating technique. In particular, bipolar PBII&D is beneficial in coating a hydrogenated amorphous carbon (a-C:H) film on a 3D target. Therefore, in this study, a-C:H films were prepared onto a complex-shaped 3D target such as macrotrench (pitch: 20 mm, aspect ratio: 1.0), microchannel (width: 100 µm, aspect ratio: 20), microtrench (pitch: 4 µm, aspect ratio: 2.0), or nanotrench (pitch: 300 nm, aspect ratio: 2.0) using bipolar PBII&D, and the film properties were evaluated. With regard to the mechanical properties, the film thickness and hardness were evaluated using a scanning electron microscope (SEM) and nanoindentation measurements, respectively. With regard to the structural properties, the microstructure of the films was evaluated by Raman spectroscopy. Subsequently, the structural and mechanical properties were compared with each other to reveal the target scale- and aspect ratio-dependence on the film properties. Furthermore, the coating mechanism was elucidated by analyzing the plasma behavior around the target using a plasma simulation method. The particle-in-cell/Monte Carlo collision (PIC-MCC) and the direct simulation Monte Carlo (DSMC) methods were simultaneously used as the plasma simulation method. Each of these is a calculation method that analyzes the behavior of ions and radicals, respectively. As a result, the a-C:H films were successfully coated onto any scale and any shape of the target. In contrast, the results of the hardness and those from the Raman spectroscopy on the sidewall surface indicated non-uniformity of the film structure and depended on the scale and aspect ratio of a target, i.e. the hardness and Raman data show different values depending on the target scale and aspect ratio. The result of the plasma simulation suggested that such non-uniform mechanical or structural properties were strongly related to the non-uniform behavior of the plasma particle incident to the sidewall depending on the scale and aspect ratio of the target. Moreover, with regard to the a-C:H films on a nanotrench, their film properties were predicted by presenting comparative discussions of the experimental measurement and plasma simulation analysis for the macrotrench, microchannel, and microtrench.

Bipolar-type plasma based ion implantation (bipolar PBII) and deposition is a promising coating technique, especially for the complex-shaped target surface. In this study, diamond-like carbon (DLC) films were prepared by a bipolar PBII technique to a trench-shaped target (20 mm pitch and 10 mm depth), and the uniformity, structural and mechanical properties of DLC films coated on the top, inside wall and bottom surfaces of the trench were evaluated by surface profilometer, Raman spectroscopy and nanoindentation hardness tests. Moreover, plasma simulation was conducted to reveal the DLC coating mechanism for finding the optimum coating conditions. Particle-In-Cell with Monte Carlo Collision (PIC–MCC) method and Direct Simulation Monte Carlo (DSMC) method were used for computing the plasma behavior. As a result, thickness uniformity of DLC films was improved with decreasing negative pulse voltage. On the other hand, the thickness of DLC films on the inside wall of the trench was much smaller than those of the top and bottom surfaces of the trench. This is because the conformal ion sheath cannot be formed around the inside wall, which in turn leads to the decrease of incidence ion flux to the inside wall, and the idea has been verified through the simulation of plasma behavior. From the Raman measurements of DLC coatings on the inside wall, it is observed that the Raman G-peak position shifts to a higher wave number and the Full Width at Half Maximum of G-peak (FWHM(G)) decreases to a smaller value compared to those of the films on the top and bottom surfaces. These indicate that the structure of DLC coatings on the inside wall surface has changed compared to those on top and bottom surfaces, i.e., graphitized, which results in the reduction of hardness.

In this study, hydrogenated amorphous carbon (a-C:H) films were deposited on a nanotrench pattern (300 nm pitch, aspect ratio: 2.0) by bipolar-type plasma based ion implantation and deposition technique (bipolar PBIID this happens due to the higher electron temperature around the nanotrench because of the surface migration of plasma particles arrived on the trench. The effects of the negative voltage on the behaviour of ions and radicals near the sidewall of the nanotrench are quite similar to those near the microtrench reported previously (Park et al 2014 J. Phys. D: Appl. Phys. 47 335306). However, the positive pulse voltage was also found to affect the behaviour of ions and radicals near the sidewall surface. The incident angles of ions on the sidewall surface increased with the positive pulse voltage because the energy of incoming ions on the trench decreases with increasing positive voltage. Moreover, the incident ion flux on the sidewall is affected by the positive voltage history. Further, the radical flux decreases with increasing positive voltage. It can be concluded that a higher positive voltage at a lower negative voltage condition is good to obtain better film properties and higher film thickness on the sidewall surface. Pattern transfer properties for the nanoimprint formed by using nanotrench molds were greatly improved by the a-C:H films owing to the resultant reduction in the mold release force.

This paper investigates the effect of different amounts of germanium oxide additive on incremental changes of fluorescence intensity of bismuth-doped silica glass (BiSG). The results indicate that the effect is more notable at a low Bi2O3 concentration (0.1 mol%) than a higher concentration of 1.0 mol%. additive. This result indicates that GeO2 additive effectively generates peculiar luminescent centers and increases the potential applications of bismuth-doped silica glass.