Electric drivetrain components operating in lubricated environments often suffer from surface degradation of bearings and gears due to electrical discharge machining. Hydrogenated diamond-like carbon (H-DLC) coatings, known for their high mechanical durability and dielectric strength, have emerged as promising protective coatings. Although coatings produced under different deposition conditions can exhibit similar mechanical properties, their electrical resistance may vary considerably. In this study, two H-DLC coatings with similar mechanical properties but distinct electrical resistance were fabricated: an ALIS-DLC (1 x 106 S2) using an anode-layer ion source, and an ARC-DLC (3 x 108 S2) using a filtered cathodic vacuum arc. The dielectric and tribological performance of these coatings was evaluated under boundary and mixed lubrication regimes. Under boundary lubrication, dielectric breakdown was the primary failure mechanism, whereas under mixed lubrication, surface degradation caused by leakage current significantly accelerated wear. In both lubrication regimes, the coating with higher electrical resistance effectively suppressed electrical damage. These results demonstrate that optimizing the insulating performance of H-DLC coatings is crucial to mitigating current-induced surface damage and ensuring the reliability of electrified drivetrain systems.

This study explores the mechanical and tribological behaviors of poly(ethylene terephthalate) (PET) substrates at the nanoscale with and without a 75 nm diamond-like carbon (DLC) coating, addressing the limitations of polymer-based nanoimprint lithography (NIL) in extreme environmental conditions. Adhesion, friction, nanoindentation, and wear characteristics were thoroughly studied with atomic force microscopy (AFM) in the temperature range of 20-80 °C and relative humidity of 30-70% RH while controlling for temperature and humidity in the AFM. The uncoated PET exhibited increased adhesion force, friction coefficient, and wear rate with an increase in temperature, particularly at temperatures that approached its glass transition temperature. The DLC-coated PET, on the other hand, preserved its low adhesion (≤87 nN), friction coefficient (≈0.08-0.10), and wear depth (∼3 nm), demonstrating excellent stability in extreme environmental conditions. Nanoindentation measurements demonstrated that the DLC coating had increased hardness and elastic modulus approximately by 900 and 180 times, respectively, and maintained its mechanical stability at 80 °C. Overall, these results affirm that DLC is an excellent candidate for a protective coating on thermosensitive polymers in NIL applications, while also providing a solid basis for increasing mold durability, pattern fidelity, and process stability in high-temperature and high-humidity environments.

Carbon-based hard coatings are ideal for mechanical materials due to their high hardness. However, maintaining low friction in air requires suppressing oxidation by atmospheric oxygen to protect the graphite structure, known for its low friction properties. This study introduced group 5 elements (vanadium, niobium, and tantalum) into the coatings to safeguard the graphite structure and enhance wear resistance through oxidation and reduction reactions. Using a ta-C coating with a high sp3 carbon structure, the effects of these elements were analyzed. The ta-C:Ta coating, containing tantalum, achieved the lowest average friction coefficient of 0.043 in air, followed by ta-C:Nb at 0.067, demonstrating the potential of group 5 elements to improve coating performance.

This study focused on the defect control in hydrogenated tetrahedral amorphous carbon (ta-C:H) deposited via the filtered cathodic vacuum arc, and investigated the corrosion behavior of ta-C:H coatings with improved surface quality under an NH4OH dilute solution. A pulsed-DC substrate bias was applied for defect control, and the surface quality was evaluated as a function of bias frequency and waveform. In addition, the wear behaviors of ta-C:H coatings were systematically investigated in ambient air, deionized water, and NH4OH suspension environments. As a result, ta-C:H coatings with high electrical resistance and reduced defect density significantly enhanced the corrosion and wear resistance in corrosive environments. The optimized ta-C:H coating exhibited a similar to 78 % reduction in corrosion current density and a similar to 55 % decrease in wear rate compared to ta-C coating under NH4OH solution. The optimized characteristics of ta-C:H coatings in this study can contribute to the improvement of the corrosion and wear resistance required for key components of ammonia-propelled ships, and are expected to provide a pathway toward reliable carbon coatings for ammonia-fueled marine engines.

Tetrahedral amorphous carbon (ta-C) coatings are widely used to enhance the mechanical reliability of mechanical systems; however, delamination and cracking frequently occur when ta-C coatings are deposited on ductile metals due to elastic mismatch and high interfacial stresses. Metallic interlayers have therefore been introduced to improve adhesion and relieve internal stress; however, the influence of interlayer deposition conditions on ta-C coatings applied to ductile metals remains insufficiently understood. In this study, the key factors governing adhesion, mechanical reliability, and crack resistance of ta-C coatings on ductile metal substrates were investigated by systematically varying the thickness and microstructure of a titanium (Ti) interlayer. A thin Ti interlayer with a porous microstructure resulted in increased wear and plastic deformation, whereas a thicker Ti interlayer with a dense microstructure significantly enhanced the mechanical properties of the coating system, leading to improved wear resistance and reduced plastic deformation. However, excessive interlayer thickness caused a reduction in adhesion and tensile properties, ultimately promoting delamination and cracking. These results demonstrate that both the thickness and microstructure of the Ti interlayer play critical roles in determining the mechanical reliability and fracture behavior of ta-C coatings on ductile metals, and further indicate that precise control of the interlayer can effectively improve overall coating performance.

This work investigates the relationship between surface microstructure, electrical conductance, and wear resistance under DC electrical current in hydrogenated tetrahedral amorphous carbon (ta-C:H) coatings. Coatings were deposited by filtered cathodic vacuum arc with hydrogen flow rates of 0–90 sccm, producing conductive sp2 clusters (areal fraction 0.25–4.71%) embedded in an insulating sp3 matrix (two-terminal resistance 31–1006 MΩ). Coatings were characterized by Raman spectroscopy, confocal laser scanning microscopy, Kelvin probe force microscopy, and breakdown voltage (VBD) measurements; lubricated ball-on-disk wear tests were run at three severity levels (0.05–0.5 A DC). Every condition was tested three times on independently deposited specimens with individually measured sp2 fractions and matrix resistances. The ta-C:H 90 sccm coating, despite the highest matrix resistance, showed the lowest breakdown voltage (18.6 V) and the lowest specific wear rate (1.43 ± 0.24 × 10-6 mm3 N-1 m-1 at 0.5 A, 96% below the most severely worn coating); damage shifted from interconnected large-scale pitting to discrete isolated pits. At the lowest severity, the four coatings were statistically indistinguishable. An effective surface conductance that treats the sp2 clusters and sp3 matrix as parallel current paths (sp2 cluster resistance 1 MΩ) ranked the coatings in inverse order of wear. Combined with the measured breakdown voltage, K ∝ VBD2/Geff collapsed all twelve specimens onto one power law (slope 1.01 ± 0.11, R2 = 0.90); microstructure alone gave the same collapse. This behavior is consistent with a current-distributing discharge mechanism: discrete sp2 pathways disperse the current before charge accumulation, linking erosion resistance to measurable surface parameters.

This study explores the tribological behavior of hydrogenated tetrahedral amorphous carbon (ta-C:H) coatings under ultra-high vacuum (UHV) conditions. The ta-C:H coatings were deposited via a filtered cathode vacuum arc, with varying hydrogen flow rates introduced during arc discharge. A ball-on-disk type vacuum tribometer was utilized to evaluate the tribological performance of those coatings against Si3N4 and ZrO2 counterparts at 0.91 N and 1.81 N. The results revealed that friction and wear behavior were significantly influenced by the hydrogen content and the mating material. Highly hydrogenated ta-C:H formed low-friction smooth tribofilms on the counterparts and itself, showing stable low friction lower than 0.05. While Si3N4 exhibited high friction due to adhesion and cold-welding, ZrO2 demonstrated low friction with the formation of flat tribofilms, even against low hydrogenated ta-C:H films. The reduced tangential friction also reduced wear between the two surfaces, resulting in a significantly low wear rate of less than 2 x 10-7mm3/N.m. Therefore, ta-C:H films could be considered a viable candidate for a tribological coating, utilized in UHV environments.

Silicon-doped tetrahedral amorphous carbon (ta-C:Si) coatings are promising materials for achieving ultralow friction in water-lubricated environments, attributed to the formation of Si(OH)x-based tribofilms. However, the deposition process via filtered cathodic vacuum arc (FCVA) often introduces large particles into the film, increasing surface roughness and causing accelerated wear during the initial sliding phase, despite the high hardness of the coating. In this study, ball-on-disk tribological tests were performed to investigate the wear behavior of ta-C:Si coatings under water lubrication. Friction coefficients, wear volume, and surface roughness were analyzed over various sliding durations. The Archard wear equation and the plasticity index were used to analyze wear and contact behavior. The friction coefficient decreased from 0.14 to 0.04 within the initial 100 m section, and the surface roughness of ta-C:Si decreased sharply from 0.35 μm to 0.01 μm based on the Rpk parameter during 10 h. Following this period, the plasticity index decreased from an initial value of 1.1 to below 0.6, transitioning to a fully elastic contact stage, marking the onset of steady-state wear after 10 h. These results indicate that the reduction in surface roughness plays a crucial role in stabilizing wear behavior and provide insights into optimizing the long-term performance of ta-C:Si coatings in aqueous environments.

In recent studies of two-dimensional (2D) nanomaterial-based solid lubricants, the importance of durability has been emerging for real engineering-scale applications. To achieve this, a transfer layer formation is essential to prevent the wear of the mechanical systems. However, it has been challenging for pristine graphene (PG) to induce a material transfer due to chemical inertness. In this study, we suggest an easy-to-process strategy to promote the huge material transfer of the PG onto the counterpart contacting material. We utilized graphene oxide (GO) as a gluing layer between the PG film and the counterpart contact surface to realize the superior tribological performance. The high interaction energy of the GO from its functional groups makes a contribution to the material transfer of PG, which is unveiled by a systematic analysis of the counterpart contact surface and the wear track. The huge solid transfer layer not only makes a wear-resistant contact interface between the transfer layer and the underlying film by densification and oxidation, but also reduces surface interaction energies, finally resulting in a significant improvement in durability.

This study investigates the microstructural, mechanical, and tribological properties of Mo-N-Cu tetrahedral amorphous carbon (Mo-N-Cu-ta-C) coatings fabricated using simultaneous filtered cathodic vacuum arc and unbalanced magnetron sputtering deposition in air (296 K) and liquid nitrogen (LN2, 77 K) environments. The 1 mu m-thick Mo-N-Cu-ta-C coating consisted of nanocomposite Mo carbide and a nanolayered Cu structure. Compared with un-doped ta-C, Mo doping reduced counterpart wear by 82 %, while Cu doping enhanced the fracture toughness by 22 % and decreased disk wear by 86 %. The addition of N2 gas further promoted phase separation, thereby strengthening the combined effect of Mo and Cu to achieve a balanced wear response. Furthermore, Cu and N2 minimized the thermal expansion and strain mismatches between the substrate and coating with decreasing temperature, thereby facilitating cryogenic applications and alleviating thermal mismatch stress. At 296 K, the Mo-N-Cu-ta-C coatings exhibited superior adhesion, controlled fracture toughness, and stable wear behavior, while maintaining reliable performance in the LN2 environment. These findings highlight that ternary metallic doping combined with nitrogen-assisted deposition provides significant advantages over conventional ta-C coatings, which closes a critical research gap for protective coatings in cryogenic conditions.

A tetrahedral amorphous carbon (ta-C) is widely used in industrial environments. However, application in extreme environments requires improved interfacial adhesion strength. This study proposes a new method to determine the adhesion strength of ta-C coating using the microtensile test, which is applied to improve the adhesion strength of ta-C coating by varying the Ti buffer layer microstructure. The tensile properties recorded in the stress-strain curve can be used to determine the difference between the absorbed energy and resistance to plastic deformation, which is then used to calculate fracture toughness. Moreover, to determine the adhesion strength, the crack density and spallation size were evaluated by measuring the cracks on the slip surface. The results show that compared to the columnar Ti buffer layer microstructure, the ta-C coating with a dense and flat Ti buffer layer microstructure more effectively improved the composite mechanical properties (columnar Ti layer H = ∼39 GPa, E = ∼430 GPa; dense Ti layer H = ∼48 GPa, E = ∼468 GPa), crack resistance (crack density = 6.4 % on columnar Ti layer; 1.5 % on dense Ti layer) and increased the dissipation energy during plastic deformation. Additionally, the dense Ti buffer layer microstructure reduced the wear rate (3.1 × 10−7 mm3/N∙m) and inhibited crack generation under long-term continuous frictional contact due to stress release in the ta-C coating. This finding clarifies the importance of the buffer layer with the suggested microstructural modifications for the wear resistance of ta-C coating.

To improve the friction and wear performance of coatings in aerospace engineering under wet and dry alternating conditions, the porous hard TiCN coating was prepared by a combination of multi-arc ion plating and oblique angle deposition. The study found that when the titanium target current was reduced from 80 A to 60 A, the pore size of the porous TiCN coating increased from 0.30 mu m to 0.93 mu m. In comparison to the low hardness of stainless steel substrate of 3.4 GPa, the hardness of TiCN coatings with pore sizes of 0.93 and 0.30 mu m rose to 10 and 22 GPa, respectively. The existence of pores can effectively improve the hydrophilicity of the coatings. However, as the pore size increased, the anti-wear lifetime of the coatings were also decrease. This process was followed by ultrasonication and hydrogen reduction of (NH4)2MoS4 to infuse MoS2 directly into the pores to fabricate the TiCN-MoS2 composite coatings. The findings revealed MoS2 atomic sheets are randomly embedded in the pores of the TiCN coating. In a stable humidity environment, as the relative humidity increased, the friction coefficient of the TiCN-MoS2 porous composite coating increased and the anti-wear lifetime decreased. In addition, the anti-wear lifetime of the TiCN-MoS2 porous composite coating at 20 % relative humidity environment is 128,322 laps, which exceeded the 38,099 laps of the dense TiCN-MoS2 composite coating. This proved that the porous composite coating had better anti-wear lifetime due to the continuous release of MoS2 in the pores under low humidity conditions. The tribological behavior of the porous composite coatings was systematically investigated under alternating humidity conditions, with a comparison against the dense TiCN-MoS2 composite coatings. The porous composite coatings possessed better self-adaptation under alternating humidity conditions, with coefficients of friction of 0.05 and 0.15 at 10 % and 70 % RH air, respectively. A detailed discussion was conducted on the relationship between tribofilm composition and tribological properties under different humidity environments.

During the fabrication process of tetrahedral amorphous carbon (ta-C) via filtered cathodic vacuum arc, inevitable surface defects arise, impacting tribological properties. Our investigation focused on the resulting deterioration in high-temperature tribological behavior. We found that by applying a duct bias to filter macroparticles, the friction-wear characteristics of ta-C could be improved. Specifically, a duct bias of 30 V reduced defect density to less 1

In this research, the fabrication of super-hydrophobic DLC coating with micro/nanoscale of the double roughening structure by employing 2.45 GHz surface-wave excited plasma (SWP) CVD and tribological evaluation of DLC coatings. The microscale friction and wear properties of super-hydrophobic DLC coating in surface wettability and wear particle generation at the running interface have been investigated. Experimental results showed that at the microscale, the friction property of DLC coatings decreases with the surface wettability and their rough morphology. In addition, the contact area of the DLC coatings decreases with the coating wettability, owing to the increases in their root-mean-square (RMS) roughness. In the case of wear, super-hydrophobicity led to the formation of small wear debris and helpful to take away out of the rubbing interface before being removed.

Tetrahedral amorphous carbon (taC) is a hydrogen-free carbon with extensive properties such as hardness, optical transparency, and chemical inertness. taC coatings have attracted much attention in recent times, as have coatings doped with a noble metal. A known antimicrobial metal agent, silver (Ag), has been used as a dopant in taC, with different Ag concentrations on the Ti64 coupons using a hybrid filtered cathodic vacuum arc (FCVA) and magnetron sputtering system. The physiochemical properties of the coated surface were investigated using spectroscopic and electron microscopy techniques. A doping effect of Ag-taC on biofilm formation was investigated and found to have a significant effect on the bacterial-biofilm-forming bacteria Staphylococcus aureus and Pseudomonas aeruginosa depending on the concentration of Ag. Further, the effect of coated and uncoated Ag-taC films on a pathogenic bacterium was examined using SEM. The result revealed that the Ag-taC coatings inhibited the biofilm formation of S. aureus. Therefore, this study demonstrated the possible use of Ag-taC coatings against biofilm-related complications on medical devices and infections from pathogenic bacteria.

We report the structure, mechanical properties, thermal stability, and durability of Si/SiC/ta-C composite (Si–ta-C) coatings fabricated using simultaneous filtered cathodic vacuum arc deposition and direct current unbalanced magnetron sputtering. Si concentration of 1.25–6.04 at.% was achieved by increasing the unbalanced magnetron sputtering power from 25 to 175 W. Si addition provided functionality to the coating, such as heat resistance, while retaining the high hardness of ta-C coatings. The Si–ta-C coatings were stable up to 600 °C regardless of the Si content, while the coating containing 3.85 at.% Si was stable up to 700 °C. The friction behavior and mechanical properties were dependent on the coating film before and after annealing at 100–200 °C; however, annealing at 300–400 °C decreased disk wear and increased counterpart wear due to an increase in film hardness on account of an endothermic reaction that increased the number of Si–C bonds. This indicates that the basic hardness characteristics of the ta-C coating and the high-temperature structural change of the Si–ta-C coating are important for ensuring high-temperature durability. These characteristics were verified through the low coefficient of friction and wear rate of the 1.25 at.% Si–ta-C coating after annealing at 500 °C.

The tetrahedral amorphous carbon (ta-C) coating is one of the fascinating surface coating for superior mechanical properties. Although its outstanding mechanical strength, it is hard to achieve adhesion stability due to high interfacial and residual stresses. Here, we introduce a new concept of pretreatment called large pulsed electron beam (LPEB) treatment. To specify the adhesion of the ta-C coating following the LPEB treatment, various adhesion tests, including the scratch test and Rockwell indentation test, were conducted. Thus, the ta-C coating pretreated with LPEB was found to have excellent adhesion through qualitative and quantitative analyses. Furthermore, to elucidate the mechanism for improving adhesion, analyses were conducted from two aspects: 1) deformation of the substrate and 2) stress change at the interface between the coating and the substrate. As a result, ta-C pretreated with LPEB increased the hardness of the substrate and supported the coating well. In addition, the thermal contraction of the coating was decreased after deposition, reducing the stress between the coating and the interface, and the adhesion was considerably improved.

The properties of tetrahedral amorphous Carbon (ta-C) film can be determined by multiple parameters and comprehensive effects of those parameters during a deposition process with filtered cathodic vacuum arc (FCVA). In this study, Taguchi method was adopted to design the optimized FCVA deposition process of ta-C for improving deposition efficiency and mechanical properties of the deposited ta-C thin film. The influence and contribution of variables, such as arc current, substrate bias voltage, frequency, and duty cycle, on the properties of ta-C were investigated in terms of deposition efficiency and mechanical properties. It was revealed that the deposition rate was linearly increased following the increasing arc current (around 10 nm/min @ 60 A and 17 nm/min @ 100A). The hardness and ID/IG showed a correlation with substrate bias voltage (over 30 GPa @ 50 V and under 30 GPa @ 250 V). The scratch tests were conducted to specify the effect of each parameter on the resistance to plastic deformation of films. The analysis on variances showed that the arc current and substrate bias voltage were the most effective controlling parameters influencing properties of ta-C films. The optimized parameters were extracted for the target applications in various industrial fields.

During running-in, there is drastic wear and the coefficient of friction (CoF) is high, because the interacting surfaces are unstable. Therefore, the running-in period should be shortened to reduce the wear of a film. When a tribofilm forms, the tribological behaviors reach a steady-state. A tetrahedral amorphous carbon (ta-C) film was irradiated with O-2 plasma, to promote tribofilm formation. This reduced the running-in cycles, CoF, and wear rate by 60%, 35%, and 62%, respectively. It was confirmed that the attractive force induced by the high surface energy agglomerated the wear debris generated during the running-in period.