Ti interlayer effectively improves the protective performance of Diamond-like carbon (DLC) coatings for Al-based alloys, by compensating for their large interfacial mismatch. However, optimization of the Ti interlayer has largely remained trial-and-error approaches, because the interface behavior under external loading has not been systematically revealed. Here, DLC around 1 mu m were deposited on Al alloys with Ti interlayer, whose microstructure was varied by changing its thickness from 0.15 to 0.97 mu m. Results demonstrated that the thickness of Ti layer had little effect on the intrinsic structure of DLC, with a critical thickness of 0.75 mu m, the Ti can effectively reduce the stress and enhance hardness of systems. Interfacial structure analysis after indentation testing affirmed that, the plastic deformation ability of Al/Ti/DLC was increased and the cracking of DLC layer towards inside was significantly suppressed. However, thin Ti layers failed to alleviate stress concentration at the Ti/DLC interface, and Ti layers thicker than the critical value developed the stronger (0002) phase orientation, which in turn sacrificed the grain boundary bonding and was destructive to its load-bearing capacity. These findings demonstrated that the Ti layer with dense structure was extremely crucial for achieving highperformance DLC coatings on Al alloys.

Polyetheretherketone (PEEK)/stainless-steel sealing pairs are key components used in the deep-sea environment. However, under high hydrostatic pressure, low temperature, and high salinity, the serious wear and corrosion of the pairs can lead to unpredictable failure. Owing to their excellent wear and corrosion protection properties, amorphous carbon (a-C) coatings have been attempted as a promising solution to this issue. However, limitations in in-situ analysis techniques and high-pressure simulation methods left the atomic-scale evolution of the a-C/ PEEK sliding interface poorly understood, leading to a lack of theoretical foundation for designing sealing pairs in a deep-sea environment. In this work, reactive molecular dynamics (RMD) simulations were performed to investigate the pressure-regulated evolution of a-C/PEEK friction interface. Results show that within 1-20 GPa contact pressure range, the friction coefficient first decreases to a minimum of 0.0333 at 5 GPa and then increases, due to the dangling bond passivation and the fluid-to-boundary lubrication transition. The influence of hydrostatic pressure becomes negligible under high contact pressures of at least 5 GPa, while a-C suppresses wear via homogeneous shear. In addition, high pressure promotes seawater ionization, enhancing Cl-/OH- adsorption that degrades PEEK's stability by attacking carbonyl groups, which elucidates interfacial failure under mechanochemical coupling, aiding high-performance deep-sea seal design.

Under high-speed and heavy-load conditions, rubber sealing products suffer severe wear, leading to reduced service life of key components of equipment. Hard and wear-resistant Diamond-like carbon (DLC) coatings offer a promising solution. While, different from DLC coated rigid substrate, the elasticity and stress distribution combining interfacial deformation of DLC-coated soft substrate show notable discrepancy during tribological test, the related wear mechanism remains poorly understood. In this study, DLC with different Si and O contents (Si/O-DLC) were deposited on nitrite butadiene rubber (NBR). With Si/O content increasing from 3.05 to 8.47 at. % and 2.42 to 7.56 at.%, respectively, the stress in DLC, the hardness and elastic modulus of DLC coated rubber tended to decrease, which enhanced adhesion strength and benefited less cracks for delamination under in-situ tensile testing. Finite element method confirmed that the synergistic improved flexibility together with the reduced mismatch of mechanical properties between Si/O-DLC and NBR, subsequently avoiding stress accumulation and suppressing cracking and spallation. All these contributions enabled the low and stable friction coefficient (COF) for the Si/O-DLC coated on the rubber, specifically with COF less than 0.38 under 5 N and 10 N. The results provide an effective strategy to improve the wear resistance of hard DLC coated flexible rubber in practical working conditions.

Constructing the periodically modulated multilayer architectures is a prevalent strategy to resolve the intrinsic trade-off between hardness and stress in diamond-like carbon (DLC) films. However, the specific dynamic contributions of distinct modulated layers to structural evolution under complex loading remain elusive. Here, the structure-property relationships of modulated DLC films were investigated at the atomic scale, spanning from energetic deposition to dynamic tribology. A counterintuitive tribological reversal governed by pressure was identified, where increasing modulation period caused a degradation in frictional performance under moderate pressure but an enhancement under high pressure. The modulation period acted as a kinetic regulator governing competitive evolution pathways. In particular, under highpressure conditions, frequent interfaces facilitated interfacial densification via energetic subplantation, transforming soft layers into a hard tribofilm that effectively supported loads through stress segmentation. Conversely, under lower pressures, shear stress was dominant, leading to the destabilization of thin layers and a consequent loss of load-bearing capacity. These findings establish a unified theoretical framework linking performance to a critical transition from shear-dominated softening to adaptive pressure-driven hardening, and thus provide essential criteria for tailoring coating architectures to specific operational contact pressures.

With high electrical conductivity and strong corrosion resistance, amorphous carbon (a-C) films are essential for ensuring the durability of metallic bipolar plates (BPs) in proton exchange membrane fuel cells (PEMFCs). However, due to the lack of plasma diagnostics and in situ electrochemical characterization, it is challenging to reveal the real-time corrosion process and to provide theoretical guidance for a-C-coated BPs. Here, we demonstrate a novel approach integrating a rotatable magnetic field with magnetron sputtering to fabricate a-C films under optimized plasma distributions. Results show that varying the magnetic field rotation angle (-60° to 90°) alters the unbalanced coefficient, plasma potential, and electron density. While the sp2/sp3-C ratio remained constant across films, the sp2 cluster diameter changed significantly. The a-C film deposited at 30° exhibited the largest sp2 cluster (La = 1.89 nm). Crucially, BPs coated with this 30° film demonstrated exceptional long-term corrosion resistance during 48 h cathodic/anodic polarization, with interfacial contact resistances of only 2.4 mΩ·cm2 before corrosion and 3.5 mΩ·cm2 after corrosion. In situ electrochemical impedance spectroscopy and scanning vibrating electrode technique analysis confirmed that performance degradation stems from localized galvanic corrosion initiation and subsequent corrosion product formation at the interface. This study emphasizes controlling sp2 clustering and density as a key design principle for enhancing a-C film durability on BPs and advances practical protective film development for PEMFCs.

Amorphous carbon (a-C) coatings are ideal surface protection materials for critical moving components in marine engineering. However, conventional metal doping and multilayer strategy cannot address the trade-off between high-load capacity and anti-tribocorrosion performance of a-C. Based on various a-C layers with similar compositions and high corrosion resistance, a soft/hard alternating diamond-like carbon (DLC)/graphite-like carbon (GLC) multilayer structure, namely (DG)10 coating, was proposed. Through a detailed investigation into crack propagation during the tribocorrosion process, results showed that, under both high (20 N) and low (10 N) loads, the (DG)10 coating demonstrated the lowest coefficient of friction (-0.06) and wear rate on the order of 10-8 mm3/N center dot m. Under low load, all three coatings could maintain their structural integrity, and the topmost carbon layer played a dominant role. While, under high load, the DLC coating showed brittle spallation due to its poor plastic deformation capability, and the GLC coating exhibited layer-by-layer shear removal and rapid consumption. For the (DG)10 coating, the multilayer structure reduced the crack propagation rate and retarded the formation of through-thickness cracks, so its damage mechanism was transformed from abrupt failure to progressive damage, and the coating only exhibited slight localized spallation within prolonged sliding time (6 h).

Amorphous carbon (a-C) films have garnered considerable attention as promising semiconductor materials for next-generation electronic devices owing to their exceptional electrical properties. However, the carrier transport mechanism of amorphous carbon films remains poorly understood, primarily attributed to their atomic structural complexity and diverse electrical behaviors. In this study, hydrogen-free amorphous carbon films were fabricated via high-power impulse magnetron sputtering. By precisely controlling the applied bias voltage, a stable sp(2) content of approximately 52% was maintained while the sp(2) cluster size (La) was varied from 1.63 to 1.93 nm. This approach enabled a systematic investigation of the correlation between the nanostructure and the resultant electrical properties. All a-C films exhibited n-type conduction with a stable electron concentration of 2.1 x 10(18) cm(-3). Their resistivity spanned 0.3-8.7 Omega center dot cm, and films with larger La values and higher structural ordering demonstrated reduced resistivity, attributed to enhanced electron mobility. Electrical transport measurements conducted over a temperature range of 100 to 350 K confirmed that charge transport is governed by a threedimensional variable range hopping mechanism. Electron hopping between adjacent sp(2) clusters predominantly dictates the electrical properties. This work provides critical insights into the structure-property relationships of a-C films and offers important theoretical and experimental support for the design and development of next-generation carbon-based electronic devices.

This study achieved friction reduction in compressor component friction pairs by applying carbon-based coating materials, exploring their tribological behaviors, and demonstrating their engineering applicability. Surface studies indicated that the coating incorporating the 2D shear layer exhibited a lower COF and reduced wear. Furthermore, wear scar analysis revealed that the shear layer was rapidly transferred to the counterface during initial sliding, where it formed a self-lubricating transfer film and frictional heat and shear forces induced the insitu generation of graphitic carbon tribofilm. Notably, the SiMo-DLC coating exhibited strong substrate adhesion and resisted delamination, thereby significantly improving the tribological performance of metallic friction pairs under compressor operating conditions. Component testing confirmed that the DLC-based coatings reduced the compressor input power and enhanced energy efficiency by up to 4%, with the best performance observed when using the SiMo-DLC coating. These results elucidate the mechanism of engineered superlubricity arising from insitu formation of graphitic structures within the transfer film, and provide experimental and theoretical support for the engineering application of carbon-based coatings in long-term service compressors.

Polypropylene (PP) nonwoven fabrics offer many advantages, such as interconnected microstructures, flexibility, and chemical stability. However, their intrinsic hydrophobicity severely restricts applications in oil-water separation. In this work, inductively coupled plasma-enhanced chemical vapor deposition (IC-PECVD) was employed to endow PP nonwoven fabrics with superhydrophilic-underwater superoleophobic properties. After hexamethyldisiloxane deposition, a subsequent 5 min oxygen plasma treatment transformed the fabric surface from highly hydrophobic (>130 degrees) to superhydrophilic (complete wetting), and from lipophilic (similar to 60.3 degrees) to underwater superoleophobic (similar to 151 degrees). The fiber surface evolved progressively from smooth to conical structure with high roughness and distributed different sizes of nanoparticles, while hydrophilic oxygen-containing polar functional groups were introduced. Importantly, the coating designed by this unique combination improved the crosslinking degree of the fiber surface, stabilized hydrophilic hydroxyl, carboxyl and other functional groups, which greatly improved the problem of plasma aging effect, maintaining high stability in air over 260 days. The long-term stability and cyclic oil-water separation tests were carried out on the pre-wetted modified nonwoven fabrics. The fabrics consistently exhibited an oil-water separation efficiency exceeding 99.0%, along with longterm stability, chemical resistance and self-cleaning capability. These results are broadening the application of modified nonwoven fabrics in the field of actual oil-water separation.

The tribological performance of amorphous carbon (a-C) and PAO oil composites is critical for mechanical system. However, the impact of unsaturated AO molecules in PAO oil on the a-C/PAO system under variable loads complicating experimental characterization and understanding of friction mechanisms. Herein, reactive molecular dynamics simulations were employed to systematically examine the influence of AO molecules on the friction behavior of a-C/PAO composite systems under variable load conditions. Results reveal distinct pressuredependent mechanisms governing the tribological behavior, highlighting the interplay between hydrodynamic lubrication and interfacial passivation. At low contact pressure, friction behavior is primarily governed by hydrodynamic lubrication, where an increase in AO chain length reduces lubricant mobility. Upon increasing contact pressure to 50 GPa, the friction interface transitions to a regime dominated by the competitive interplay between hydrocarbon passivation and C-C bond formation, but the degree of interfacial passivation induced by AO molecules results in variations in friction performance. As pressure further reverts to 5 from 50 GPa, the fracture of long-chain AO molecules into shorter fragments weakens the difference in interfacial structures between systems. These results deepen the understanding of friction mechanisms involving AO molecules in a-C/ PAO systems and provide theoretical guidance for designing high-performance lubrication systems.

Amorphous carbon (a-C) coating can effectively reduce wear of the counterpart PEEK components in engineering equipment. While, the tribological performance of both a-C and PEEK demonstrates pronounced sensitivity to ambient atmosphere. Here, tribological behaviors of a-C/PEEK were compared under various environments including atmosphere, vacuum, and O2, the interfacial tribo-chemical reaction was discussed from experimental investigation and atomic-level simulations. Results show that, oxygen content is one key factor to influence interfacial tribo-chemical reaction and wear mechanism for a-C/PEEK pair. Under ambient atmosphere and O2, oxygen molecules break molecular chains of PEEK, even bond or absorb on the a-C under higher oxygen content, which can hinder the formation of the transfer film and result in elevated COF and worse wear of PEEK.

This study investigated the effects of various Si, Al, and SiAl interlayers on the mechanical and tribological properties of hydrogen-free DLC coatings deposited on 316L stainless steel (316LSS). Using a Si single-interlayer resulted in high oxygen concentration at the DLC interface, adversely increasing residual stress and degrading adhesion. However, the SiAl interlayer significantly enhanced the mechanical properties of DLC, increasing its hardness from 14.5 to 17.8 GPa. In addition, the SiAl interlayer drastically reduced the high compressive stress of non-interlayered DLC from 0.68 GPa to 0.23 GPa, while the Si interlayer only slightly decreased it to 0.61 GPa. The Si and SiAl interlayers improved the tribological properties of DLC to withstand loads at 5 N, 7 N, and 10 N. In contrast, non-interlayered DLC and Al/DLC coatings peeled off under 7 N. Notably, SiAl/DLC illustrated better tribological properties than Si/DLC. Under 10 N, Si/DLC coating showed the coefficient of friction COF, wear rate, and Hertzian pressure at 0.13, 4.43 (10- 7 mm3/N.m), and 1.45 GPa, respectively, while those of SiAl/DLC coating were 0.12, 3.41 (10- 7 mm3/N.m), and 1.39 GPa. Meanwhile, the SiAl/DLC coating also maintained a high lubrication effect of the tribo-film, which favored excellent tribological properties. These findings identified that introducing SiAl interlayer could be a strong strategy to improve both the mechanical and tribological properties of hydrogen-free DLC coatings on 316LSS.

Cr2AlC, a representative MAX phase, gains increasing attention for the excellent oxidation tolerance and corrosion resistance used in harsh high temperature and strong radiation environments. However, the lack of the phase formation mechanism has become the key bottleneck to the practical applications for Cr2AlC synthesis with high purity at low temperatures. In this work, we fabricated the amorphous Cr–Al–C coating by a hybrid magnetron sputtering/cathodic arc deposition technique, in which the in-situ heating transmission electron microscopy (TEM) was conducted in a temperature range of 25–650 ℃ to address the real-time phase transformation for Cr2AlC coating. The results demonstrated that increasing the temperature from 25 to 370 ℃ led to the structural transformation from amorphous Cr–Al–C to the crystalline Cr2Al interphases. However, the high-purity Cr2AlC MAX was distinctly formed at 500 ℃, accompanied by the diminished amorphous feature. With the further increase of temperature to 650 ℃, the decomposition of Cr2AlC to Cr7C3 impurities was observed. Similar phase evolution was also evidenced by the Ab-initio molecular dynamics calculations, where the bond energy of Cr–Cr, Cr–Al, and Cr–C played the key role in the formed crystalline stability during the heating process. The observations not only provide fundamental insight into the phase formation mechanism for high-purity Cr2AlC coatings but also offer a promising strategy to manipulate the advanced MAX phase materials with high tolerance to high-temperature oxidation and heavy ion radiations.

This study investigated the friction mechanisms of textured amorphous carbon (a-C) films under solid-liquid composite conditions using reactive molecular dynamics simulations, focusing on the effects of varying oil content and contact pressure. By quantifying the impact of these factors, the optimal preparation of a-C films for different operating conditions was guided. Results indicate that friction performance is closely related to the lubrication state, which is determined by the coupling of oil content and contact pressure. The potential lubrication mechanisms depend mainly on the fluidity of the lubricant, the bonding between a-C surfaces, and the competitive or synergistic effects of the lubricant and interface passivation in the H-stress state. Most importantly, the Pearson correlation coefficient reveals that rectangular groove textures exhibit high sensitivity to the application environment, and the optimal application scenarios for different textured surfaces are suggested. These insights underscore the importance of selecting appropriate textured types and adjusting lubrication strategies to enhance the tribological performance of a-C films under various operating conditions.

Carbon-based coatings have been successfully utilized in aerospace, automobiles, and ocean exploration, as typical solid lubricants. Particularly, amorphous carbon coatings (a-C:H) have been employed on kinematic pairs of advanced equipment, such as polyether ether ketone (PEEK)/steel pair, for enhancing their wear resistance and solid lubricity. However, the significant disparity in mechanical properties between PEEK and a-C:H and the poor interface adhesion strength are the key factors that limit the further improvement of tribological performance. In this study, based on the gradient transition of composition and mechanical properties between PEEK and a-C:H, a-C:H/a-C:H:Si:O functionally graded coatings (FGCs) were fabricated on PEEK. The friction behavior of the a-C:H/a-C:H:Si:O FGCs coated PEEK sliding against 304 stainless steel was performed in dry atmosphere using a ball-on-plate reciprocating tribometer. Compared with the single-layer a-C:H and a-C:H:Si:O coated PEEK, the friction stability period of FGCs is extended by at least 33 %. When the thickness ratio of a-C:H/a-C:H: Si:O is 1/1, the wear rate of FGC is as low as 5.6 x 10-7 mm3/Nm. The excellent tribological performances of FGCs can be attributed to the appropriate mechanical property transition and strong adhesion strength between the coatings and the PEEK. The finite element simulation results indicate that the FGCs can provide more excellent deformation resistance and can also significantly eliminate stress concentration. This work can provide basic theoretical guidance for preparing functionally graded amorphous carbon coatings on PEEK to achieve excellent tribological and wear performance.

Diamond-like carbon (DLC) films possess excellent mechanical and tribological properties, while their atomicscale residual stress regulation remains challenging for widespread applications. In this study, the effects of single-energy and alternating-energy deposition strategies on the growth, structural characteristics, and tribological properties of diamond-like carbon (DLC) films are investigated systematically using molecular dynamics simulations. Results reveal that the alternating-energy deposition strategy significantly reduces the residual stress of DLC film by optimizing the modulation ratio (lambda = 1.3) of film thickness at 1 eV/atom to that at 70 eV/ atom, achieving a maximal 85 % drop of residual stress, compared to that observed in single-energy deposition systems. This structural heterogeneity regulates local strain fields and disrupts continuous stress networks, effectively reducing overall residual stress. Tribologically, the alternating-energy system, particularly the softhard alternating configuration (1-70 eV), demonstrates lower friction coefficient than that in the hard-soft alternating case. This attributes to its periodic soft-hard alternating surface structure and the formation of a graphene-like layered architecture during the friction process, which minimizes the friction through weak van der Waals interactions and uniform stress distribution. These results highlight the potential of alternating-energy deposition for optimizing DLC film properties and provide theoretical foundation and experimental guidance for designing DLC films with low stress and high tribological performance.

Compared with silicon and polysilicon piezoresistive materials in MEMS, diamond-like carbon (DLC) films are promising candidates for applications in harsh corrosive environment. However, the underlying mechanism between piezoresistive properties and carrier behavior is still lacking study yet due to the complexity in atomic bonds. To develop new carbon-based sensors for harsh environments, we synthesized the Cr-containing DLC films with Cr content changed from 0.64 to 23.17 at.%. The results showed that increasing Cr content enhanced the conductive phases distributed in the amorphous sp3 matrix. Nevertheless, a small amount of Cr3C2 nanocrystals formed when Cr content reached 11.05 at.%. All Cr-DLC films exhibited the semiconductor behavior in the range of 150-350 K. However, the threshold voltage of I-V plot disappeared once the Cr content exceeded 11.05 at.%. Similarly, the optical bandgap decreased from 3.55 to 2.49 eV as Cr content increased from 0.64 to 23.17 at.%. The Fermi level was closer to the valence band edge, indicating p-type semiconductor characteristic. For the sample with an appropriate Cr content of 1.38 at.%, it had the highest gauge factor of 22.8. Its minimum valence band offset of 0.89 eV resulted in a significant change in the tunneling process under applied strain, which explains its notable piezoresistive effect.

The combined design of lubricating oil and textured surfaces can optimize the friction performance of amorphous carbon (a-C) films. However, due to the limitations of experimental characterization methods, the impact of sliding direction on the friction behavior of textured a-C films remains unclear, particularly regarding the mechanisms of interface structural transformation and lubricating oil flow behavior. Therefore, this study constructed rectangular textured a-C films and investigated the effect of sliding angle on the tribological properties of a-C under oil lubrication condition by reactive molecular dynamics simulations. Results indicate that the friction properties of a-C films are significantly influenced by the sliding angle. As the sliding angle increases from 0 degrees to 60 degrees, the friction interface dominated by the passivation process, exhibits an increase in saturated bond content, leading to a reduction of the friction coefficient at 30 degrees and 60 degrees. However, when the sliding angle reaches 90 degrees, the lubricating oil is primarily concentrated between the textured protrusions and the upper friction pair, leading to a failure in the oil storage function of the textured layer and an increase in the friction coefficient. These findings reveal the friction mechanisms of a-C films induced by sliding angle, effectively guiding the design and technical application of textured a-C films.

Polyether ether ketone (PEEK) is widely used in aerospace applications because of its excellent physical and mechanical properties. However, given its intrinsic viscoelasticity and low hardness, PEEK is prone to wear failure. To address this problem, a carbon-based film deposition technology is typically applied. Among these films, diamond-like carbon (DLC) films have attracted considerable attention owing to their high hardness, good wear resistance, and chemical inertness. Using a linear ion beam combined with direct current magnetron sputtering technology, W-DLC films with different doping contents were prepared on PEEK by varying the Ar / C(2)H(2 )flow ratios from 68 / 12 to 62 / 18. The effects of the gas flow ratio on the composition, microstructure, and mechanical and friction properties of the PEEK / W-DLC composites were systematically examined. The SEM and HRTEM results showed that as the Ar / C2H2 flow ratio decreased, the deposition rate of the film gradually increased, the carbon clusters densified and their size increased. As the gas flow ratio decreased, the size of W clusters decreased, leading to a decline in the content of highly crystalline WC1-x. Moreover, when compared with pure PEEK, the surface wrinkle density of the PEEK / W-DLC composites increased and mechanical interlock structures were formed at the interface. The X-cut test showed that as the gas flow ratio decreased, the interfacial adhesion weakened, and the peeling of the films tended to become obvious. The XPS data showed that the W content decreased from 7.08at.% to 2.63at.%. The increase in C content resulted in the formation of more C- C bonds, and some of C=O bonds preferentially transformed into C- O bonds. With a decrease in the gas flow ratio, the W0 content decreased, whereas the W5+ / W6+ content increased slightly. This indicated that the W element in the film tended to exist in the form of W carbides. Raman analysis showed that I-D /I-G decreased from 0.42 to 0.32, the sp(2) content and cluster size decreased accordingly. The full width at half maximum (FWHM) of G peak increased from 62.67 cm(-1) to 71.26 cm(-1), indicating that the incorporation of W atoms could aid in reducing the structural disorder in films. As the gas flow ratio decreased, the hardness (H) and elastic modulus (E) of the PEEK / W-DLC composites reached to 5.25 and 30.23 GPa, respectively. Compared to pure PEEK, the values of H and E both increased by an order of magnitude. When the gas flow ratio was 66 / 14, the H / E and H-3 / E-2 of the composite corresponded to 0.2 and 0.17, respectively, which were approximately two orders of magnitude higher than those of pure PEEK. This implied that the composite had strong fracture toughness and good elastic-plastic deformation resistance. Compared with other samples, the W-DLC films prepared with 66 / 14 flow ratio exhibited better tribological properties with a low wear rate of 1.52x10(-8) mm3 / (Nm). This was mainly owing to the mechanical protection of the carbon films (improving wear resistance) and W-rich lubrication transfer film formed at the wear scars (reducing friction factor). By analyzing the formation mechanism of the pits on the PEEKA/ W-DLC composites, it was determined that owing to the viscoelasticity of PEEK and the generation of wear debris of W-DLC films, both adhesive wear and abrasive wear occurred during the friction process. The pits that formed on the wear tracks mainly existed in the following three forms: the first type of pit was mainly composed of C elements, while the distributions of O, Fe, and W elements were hardly observed. This indicated that during the friction process, the wear debris of W-DLC films formed C-rich clusters. These C-rich clusters were embedded in the low-hardness PEEK substrate by frictional compressive stress. The second type of pit was mainly composed of C and O elements, whereas W and Fe elements were rarely distributed. These pits were caused by the peeling of W-DLC films, which led to the exposure of PEEK substrate. The third type of pit was mainly composed of C, O, and Fe elements, while the presence of W element was relatively rare, and Fe element was concentrated on the convex part of the pits. The convex part was formed by the accumulation of wear debris in the pits. This showed that the first type of pit further caused abrasive wear on the grinding ball due to the convex part. This research not only reveals the structural evolution and wear failure mechanism of carbon-based films on PEEK, but also guides the design of high-efficiency wear-resistant aerospace materials.

Tribocorrosion is a material-degradation phenomenon resulting from interactive effects between wear and corrosion. For various marine equipment, their key metal motion systems are typically affected by the combined effect of mechanical wear and chemical corrosion under the harsh marine environment, which can directly limit their stability and safety. Thus, comprehensive investigations into tribocorrosion behavior is critical for the design of appropriate engineering materials under the marine environment. Advancing marine exploration and deep-sea development necessitates surface and coating techniques to ensure favorable anti-corrosion and anti-wear performances for moving mechanical components. Many conventional techniques have been used to prepare protective coatings, such as spraying, high-energy beam surface modification, and physical vapor deposition (PVD). Among the diverse developed protective coatings, those realized via PVD exhibit favorable properties, including high corrosion resistance and excellent mechanical performance, which can effectively protect precision moving components used in deep-sea or offshore mechanical systems; thus, they are one of the most effective strategies in this field. This article focuses primarily on the development of anti-tribocorrosion coatings achieved via PVD and technologies used in the marine environment, in addition to the main scientific and technical issues encountered in the field. First, the tribocorrosion performance of carbon-based, nitride-based, high-entropy alloy, and transition metal dichalcogenide coatings are introduced, and the role of components and multilayer / nano-multilayer / nanocomposite / gradient structures on their tribocorrosion performance and related failure mechanism are summarized. The multilayer interface in coatings achieved via PVD not only significantly improves their hardness by hindering dislocation movement but also improves their corrosion resistance by hindering the diffusion of H2O, O2, Cl-, and Na+ corrosives. To evaluate the tribocorrosion performance of coatings, electrochemical and tribological tests are primarily conducted in early research; currently, tribocorrosion tests are performed using a tribometer equipped with a three-electrode electrochemical system. By adopting in-situ atomic force microscopy (AFM) and an AFM-based "image-wear-image" tribology method, researchers are currently investigating subnanoscale and nanoscale wear, the tribocorrosion phenomenon, as well as the oxide growth mechanism of metallic materials. For advanced synergistic wear-corrosion models, a novel two-dimensional predictive model has been developed for predicting the synergetic wear-corrosion reliability of Ni / GPL and steel. Additionally, a combined experimental and computational investigation has been performed using Al single crystals to develop a crystal-based tribocorrosion modeling framework that considers the effects of lattice reorientation and dislocations on surface corrosion. Additionally, new strategies that combine PVD with other surface-protection technologies have been developed, for example, duplex coating systems formed via the PVD of CrN or carbon-based coatings and thermal layer spraying using a high-velocity oxyfuel. Using these methods, material losses due to the synergistic effects of wear and corrosion can be reduced. In particular, hydrogenated carbon-based coatings present high tribocorrosion resistances under low loads due to their high hardness and excellent corrosion resistance; however, they exhibit catastrophic delamination under heavy loads, whereas hydrogen-free carbon-based coatings exhibit better tribocorrosion performance owing to their gradual shearing characteristic. Additionally, carbon-based coatings can enhance the anti-corrosion properties of microarc oxidation (MAO) coatings on magnesium alloys. The superior low-friction and anti-corrosion properties of carbon-based coatings / MAO render them preferable as protective coatings on magnesium alloys. Cr layers achieved via thermal diffusion metallization and CrN coatings deposited via PVD are used to strengthen the surface of 45 steel, thus improving its surface hardness and abrasion resistance. By implementing ion implantation and Al / AlN / CrAlN / CrN / MoS2 gradient duplex coatings, both the anti-wear and anti-corrosion properties of AM60 magnesium alloy are improved. For AISI 4140 steel, plasma nitriding applied before the coating significantly improves the corrosion and tribocorrosion resistances of PVD CrN, TiN, and AlTiN coatings. Typical applications of anti-tribocorrosion coatings achieved via PVD include seawater-pump plungers, hydrostatic slipper bearings, ball valves, and components of a helicopter-cockpit instrument panel. Hydrogenated diamonds coated with Cr and WC as transition layers are prepared on the plunger of marine diesel engines. These coatings can significantly improve the hardness and elastic modulus while decreasing the friction factor under heavy-diesel-oil environments. After a bench test is performed, the wear marks on the surface of the plunger with coating are extremely narrow and shallow. For drill pump valves, implementing TiN coatings can increase their service life by three times. In the cockpit of a helicopter, multigradient nano-black coatings achieved via PVD are thin and the thickness tolerance is low; additionally, these coatings satisfy the requirements of the salt spray test. Finally, the development and application of anti-tribocorrosion coatings achieved via PVD under the marine environment are proposed. Machine-learning and big-data sharing services should be used to comprehensively understand the damage mechanism; the optimization and design of the suitable coating should account for the actual operating conditions, such as deep sea, nearshore, and shallow sea; advanced coating equipment should be developed for the inner wall of certain pipelines; and in-situ evaluations and bench experiments should be performed to evaluate the service life of metal mechanical components and coating materials. This review presents a comprehensive and systematic report pertaining to anti-tribocorrosion coatings achieved via PVD for marine applications.