Search Results (278)

With the increasing demands on energy efficiency and dynamic stability of modern combustion engines (e.g., TDI systems), conventional powder metallurgy materials are reaching their limits in terms of fatigue life and surface integrity. This scientific problem has led to the need to develop hybrid metal matrix (MMC) systems that use in situ hard phase formation. This study presents a comparative analysis of two real industrial components representing hybrid systems with a uniquely high content of titanium and vanadium (>1% by weight). The Ni-Mo-Ti system and the high-carbon C-Cu-Ti system were compared. The samples were processed by steam oxidation and plasma nitriding at 200 °C after sintering. The experimental methodology included chemical analysis on the Bruker Q2 ION 2 instrument, 10-point EDX analysis (Phenom), measurement of the apparent hardness of HV10 and dynamic ball-on-disc tribological tests at a load of 5.00 N supplemented by 3D profilometry. The results showed that the Ni-Mo-Ti system achieves higher hardness at functional edges (256 HV10) and three times higher resistance to deep penetration (11.46 μm vs. 34.67 μm) compared to the C-Cu-Ti system. Topographic analysis confirmed the positive role of porosity as a micro-reservoir for abrasion particles (negative Ssk). The study confirms that the nickel–molybdenum matrix ensures more efficient fixation of in situ generated TiC carbides, thus providing higher functional stability for automotive applications, which was verified by the non-destructive vibroacoustic diagnostics of Polytec PSV-500. Full article

Silver-doped diamond-like carbon (Ag–DLC) coatings were investigated with respect to their tribological behavior under ambient and physiologically relevant conditions. Gradient Ag–DLC coatings deposited on AISI 316L stainless steel were tested in air, simulated body fluid (SBF), and an albumin-containing solution using a pin-on-disk configuration. Increasing silver content resulted in a systematic reduction in the H³/E² ratio, leading to increased coating wear irrespective of the environment. In contrast, friction behavior was strongly controlled by the surrounding medium. Under dry sliding in air, all coatings exhibited similar steady-state friction governed by the DLC matrix. The lowest steady-state friction coefficients were obtained in SBF, indicating that the aqueous ionic environment provided the most favorable friction conditions among the tested media. In the albumin-containing medium, friction also remained low, indicating that protein adsorption and interfacial layer formation modified the sliding conditions, although the CoF did not fall below that observed in SBF. Wear was highest in air and generally lowest in SBF, while tests in albumin promoted surface layer formation. Surface analyses indicated silver redistribution, transfer-layer formation, and the presence of protein-related surface agglomerates, with higher apparent surface coverage on coatings containing more Ag. Overall, the results show that Ag-doped DLC coatings exhibit environment-dependent tribological behavior under physiologically relevant conditions. The present work should be regarded as a tribological study rather than a direct validation of antibacterial performance. Future studies should combine tribological assessment with dedicated antibacterial and cytocompatibility experiments. Full article

To address the severe wear and galvanic corrosion of TC4/Mg three-dimensional interpenetrating composites caused by the potential difference and hardness disparity between the two phases, this work proposes a hybrid surface modification strategy combining plasma electrolytic oxidation (PEO) with a self-assembled monolayer (SAM) doped with multi-walled carbon nanotubes (MWCNTs). A PEO ceramic coating was first grown in situ on the composite surface, followed by sealing modification using MWCNTs-containing SAM. The microstructure, phase composition, tribological behavior and potentiodynamic polarization curves of the coatings were systematically evaluated. The results show that the PEO coating is mainly composed of Mg₂SiO₄, MgO, MgF₂ and TiO₂, exhibiting a typical porous structure. After the MWCNTs-doped SAM composite modification, the nano-fillers and the molecular layer synergistically seal the micropores and cracks, and the surface transforms into a continuous and dense layered morphology. Wear tests reveal that the composite coating reduces the friction coefficient to 0.195 and decreases the wear volume by 93.53% compared with the bare composite. The “micro-roller bearing” effect and debris adsorption of MWCNTs significantly improve the wear resistance, and the dominant wear mechanism changes from abrasive wear to three-body wear. Electrochemical measurements show that the corrosion current density of the composite coating decreases from 2 × 10⁻⁴ A·cm⁻² (bare composite) to 1.401 × 10⁻⁹ A·cm⁻², i.e., a reduction by five orders of magnitude, with a protection efficiency of 99.99%. This is attributed to the physical barrier effect of the PEO coating and the synergistic sealing of defects, as well as the blocking of electron transfer by MWCNTs/SAM. The multi-level protection system of “PEO + MWCNTs + SAM” constructed in this work achieves a synergistic improvement in both wear resistance and corrosion resistance of the TC4/Mg two-phase interpenetrating composite, and holds promise for further investigation as an osseointegration implant material. Full article

To further improve the high-temperature dry sliding performance of Si₃N₄ ceramics, a CrAlN transition layer was introduced to improve interfacial stability, while Ag was incorporated as a solid lubricant into the CrAlN matrix. The effects of Ag content on the microstructure and mechanical properties of the coatings were systematically examined, and the tribological performance was evaluated from 25 °C to 550 °C under dry sliding conditions. The Ag concentration increased with increasing Ag target power and affected the morphology, nanoparticle distribution, surface roughness, and mechanical properties of the coatings. Among the tested samples, the coating containing 9.6 at.% Ag exhibited a comparatively favorable combination of mechanical properties within the investigated composition range, with a hardness of 11.5 GPa, an H/E ratio of 0.0913, and an H³/E² value of 0.096 GPa. Tribological tests showed that the average coefficient of friction decreased from 0.32 at 25 °C to 0.12 at 550 °C. This reduction may be associated with temperature-assisted Ag redistribution toward the worn surface and the possible development of Ag-rich surface features at elevated temperatures. However, the wear rate increased with temperature, reaching 3.6 × 10⁻⁵ mm³/(N·m) at 550 °C, suggesting that friction reduction was accompanied by increased material removal and possible near-surface weakening. These results indicate that controlling Ag content is important for balancing friction reduction and wear resistance in ceramic-based self-lubricating coatings. Full article

TiN coatings have been widely employed in cutting tools due to their high hardness and excellent wear resistance. While most research on nitride coatings has focused on binary (e.g., TiN) and ternary (e.g., TiAlN, TiSiN) systems, the quaternary TiMoSiN system remains comparatively underexplored. In response to the growing demand for comprehensive coating performance under increasingly complex working conditions, this work incorporates Mo and Si into the TiN system to synergistically enhance mechanical, tribological, and corrosion-resistant properties. TiMoSiN coatings were deposited onto cemented carbide substrates by arc ion plating using a Ti_0.8Mo_0.1Si_0.1 alloy target. The influence of nitrogen partial pressure (0.2–1.7 Pa) on the microstructure, mechanical properties, tribological behavior, and electrochemical corrosion performance was investigated. The results show that nitrogen partial pressure plays a critical role in regulating the chemical composition, phase structure, and preferred orientation of the coatings. As the nitrogen partial pressure increases, surface macroparticles are reduced, while the Ti and Mo contents decrease and the Si and N contents increase. The phase structure evolves from a dual-phase mixture of TiN and Ti₂N to a single TiN phase, accompanied by a shift in preferred orientation from (111) to (200). The hardness of the coatings ranges from 36.2 to 43.1 GPa, reaching a maximum of 43.1 GPa at 1.0 Pa. The coating deposited at 0.6 Pa exhibits the best overall performance: it achieves the lowest friction coefficient (0.349) and wear rate (1.08 × 10⁻⁷ mm³/(N·m)), together with the highest corrosion resistance, as reflected by the most noble corrosion potential (−152 mV) and the lowest corrosion current density (8.99 × 10⁻⁸ A·cm⁻²). This study demonstrates that nitrogen partial pressure effectively controls the microstructure and multifunctional properties of TiMoSiN coatings, providing practical process guidelines for their application in demanding cutting environments. Full article

CrN/DLC composited coatings were deposited on 431 stainless steel, and their structure was analyzed, with particular emphasis on the influence of CrN content on the coating properties. X-ray photoelectron spectroscopy (XPS), nanoindentation testing, scratch testing, and reciprocating tribometry were employed to characterize the chemical composition, mechanical properties, adhesion strength, and tribological performance of the coatings, respectively. Structural analysis indicates that when the ratio of CrN/Cr₂N is relatively low (<1), a high content of chromium dinitride (Cr₂N) is formed in the interlayers, resulting in a porous and loose coating structure. When the ratio achieves 1:1, an optimal balance, with the CrN content reaching a maximum of 21.04% and the Cr₂N content decreasing to a minimum of 20.68%, the densification degree of the coatings is increased, the coating adhesion strength is improved to 11.87 N. Meanwhile, the enhanced formation of the CrN phase improves the hardness to 12.27 GPa. Tribological test results demonstrate that when the ratio is approximately 1:1, the coating exhibits the lowest friction coefficients under dry sliding, deionized water, and artificial seawater conditions (0.0932, 0.1409, and 0.1021, respectively), as well as the minimum wear rates. With the decrease in CrN content of the coatings, the interfacial mismatch degree of the coatings is aggravated, which leads to not only more interfacial defects but also a relatively loose structure, as well as a decrease in the bonding strength (6.81 N), hardness (5.22 GPa), and deformation resistance. Therefore, an excessive Cr₂N phase may degrade the hardness-to-elastic modulus ratio (H/E) of the coatings by increasing interfacial mismatch and reducing structural compactness. Full article

The development of resin-regolith composites represents a promising In Situ Resource Utilization (ISRU) strategy for future lunar missions. While unsuitable for primary habitat construction due to the payload cost of transporting polymers from Earth, these composites offer a highly efficient solution for manufacturing non-structural, everyday items (e.g., containers, tools, and plant cultivation pots) directly on the Moon via mold–casting. This approach significantly reduces the volume and mass of pre-formed plastic payloads. In this work, the influence of the particle size distribution of a lunar highland simulant (LHS-1E) on the mechanical properties of epoxy-based composites was systematically investigated for such applications. First, the regolith-to-resin ratio was optimized for castability, establishing a maximum regolith content of 60 wt.%. Then, four different size fractions of the simulant were prepared by sieving (>200 µm, 200–100 µm, 100–50 µm, and <50 µm), and composite samples were cast maintaining this optimal ratio. X-ray microtomography revealed that using larger particles (>200 µm) increased composite porosity, whereas smaller fractions promoted more compact structures. Three-point bending tests showed that intermediate particle sizes (200–100 µm and 100–50 µm) led to enhanced flexural strength, while the smallest particles (<50 µm) decreased mechanical performance, likely due to a lower basalt content in this finer fraction. Finally, ball-on-disk tribological analyses highlighted that composites made with larger particles (>200 µm) exhibited superior wear resistance, whereas particle size had negligible effects on the coefficient of friction. Overall, the results demonstrate that both particle size and mineralogical composition significantly influence the performance of regolith–epoxy composites, providing essential guidelines for the in situ manufacturing of functional, non-structural objects for lunar outposts. Full article

HfC, TaC, and HfTaC composite coatings were successfully fabricated on SiC-coated carbon/carbon (C/C) composites using the double glow plasma alloying (DGPA) technique. The microstructure, mechanical properties, and tribological behaviors of the coatings were systematically investigated. The HfTaC coating exhibited a dense and uniform structure with good interfacial integrity and a compositionally graded transition layer, effectively relieving thermal stress. The hardness of HfTaC and HfC coatings (approximately 12 GPa) was higher than that of the TaC coating. Moreover, the higher K value (1.02) and H/E ratio (H/E = 0.09, H³/E² = 0.085 GPa) indicate that the HfTaC coating exhibits good load-bearing capacity and toughness. Under both 5 N and 15 N loads in the reciprocating friction, the HfTaC coating maintained the lowest and most stable friction coefficient (~0.18). Under the 15 N load, it exhibited the smallest specific wear rate. Observation of the wear scars revealed that the HfC and TaC coatings suffered from pore formation and flake-like spallation, while the HfTaC coating retained structural integrity with only minor cracks. In high-temperature ball-on-disc friction tests up to 500 °C, the wear mechanism of the HfTaC coating gradually transitioned from mild abrasive wear to severe oxidative and adhesive wear, yet the HfTaC coating still provided effective protection. These findings demonstrate that the DGPA-fabricated HfTaC coating is a promising candidate for enhancing the wear resistance and service durability of C/C composites. Full article

Titanium alloy is difficult to cut, with tools prone to adhesion and diffusion wear that reduces life and surface quality. Traditional coatings fail to meet precision machining demands. Based on TiAlN, Ce-doped coatings were prepared via magnetron sputtering at varying powers to investigate mechanical and tribological properties. The results show that with the increase in Ce doping amount, the hardness, elastic modulus, H/E, and H³/E² ratios of the coating increase first and then decrease, and the friction coefficient decreases first and then increases. The performance is optimal at 50 W, the friction coefficient is 0.676, and the film-based adhesion is 113.8 N. Compared with the TiAlN coating, the hardness increased by 12%, the wear loss decreased by 24%, and the H/E and H³/E² increased by 31% and 95%, respectively. The mechanism analysis shows that the appropriate amount of Ce doping can improve the toughness of the coating by grain refinement and solid solution strengthening and significantly inhibit adhesive wear and oxidative wear. Ce-modified tools were further prepared for titanium alloy turning experiments. Compared with uncoated and traditional TiAlN-coated tools, Ce doping can effectively reduce tool wear and improve the surface quality of the workpiece and has significant advantages under high-speed and large cutting depth conditions. This study systematically reveals the adaptive lubrication mechanism of Ce-doped TiAlN coating in the cutting process of titanium alloy and provides theoretical support and engineering guidance for the preparation of special tool coatings for difficult-to-machine materials. Full article

Diamond-like carbon (DLC) coatings are increasingly explored as a practical route to enhance the surface performance of biomedical implants and tissue engineering scaffolds, particularly when combined with additive manufacturing. Rather than serving only as protective layers, DLC coatings allow for independent tuning of surface properties without modifying the bulk structure, which is especially relevant for complex 3D-printed components. This flexibility is often what makes them attractive for biomedical design. This review is structured around two main application areas: DLC coatings for prosthetic implants and DLC coatings for tissue engineering scaffolds. Within this context, the influence of DLC structure (e.g., sp²/sp³ bonding, hydrogen content, and doping) on mechanical, tribological, and biological behavior is discussed. Particular attention is given to additively manufactured metallic implants and porous scaffolds, where large surface area and internal architectures complicate coating uniformity and adhesion. Reports show that DLC coatings can improve corrosion resistance, reduce wear, and influence biological responses, such as antibacterial activity and cell interactions. Several challenges remain to be solved, especially in achieving uniform coating penetration in porous networks and in ensuring long-term stability under physiological conditions. The combination of additive manufacturing and DLC coatings has been shown to offer the potential to become an enabling technology for next-generation biomedical devices. Full article

Two-dimensional (2D) materials are promising candidates for nanoscale wear-protective coatings. The mechanisms governing their tribological behaviour (i.e., friction and wear) are material-dependent. In this work, we use atomistic molecular dynamics simulations to investigate nanoscale sliding, friction, and lithographic tracks in two 2D materials, graphene and MoS₂, both placed on a SiO₂ substrate. Our results reveal fundamentally different deformation mechanisms in the two materials, where deformation comes as a consequence of applied normal load. MoS₂ deforms via the formation of a stable out-of-plane pucker beneath the contact, enabling efficient absorption and elastic redistribution of mechanical energy within the coating as well as simultaneous reduction of plastic deformation of the underlying material. Wear prevention in the substrate comes at the cost of localised damage to the MoS₂ layer along the sliding path once it reaches the rupture point. On the contrary, graphene exhibits strongly localised deformation due to its high in-plane stiffness and atomic thickness, leading to plastic deformation of the underlying material and mitigating layer damage. These findings provide clear design guidelines for 2D coatings in nanotribological applications, and highlight layered materials, such as MoS₂, as particularly effective for wear protection. Full article

Permanent magnet synchronous motor (PMSM)-driven position servo systems in high-speed flight vehicles face severe challenges from extreme thermal environments, which induce significant parameter variations up to 25% (e.g., motor torque constant) and complex multi-scale disturbances. This paper proposes a novel adaptive robust control strategy integrating three key components: (1) an ultra-local model formulation motivated by physically consistent thermal effect analysis of electromagnetic, mechanical, and tribological parameters; (2) a dual-layer disturbance observer architecture comprising a third-order finite-time convergent extended state observer (FTCESO) for fast-varying disturbances and a σ-modification adaptive estimator for slow-varying thermal drifts; and (3) a global nonlinear integral terminal sliding mode controller with a cycloidal reaching law. Stability analysis based on homogeneous system theory and Lyapunov methods establishes practical finite-time convergence with explicit bounds. The experimental results on a TMS320F28335-based servo platform demonstrate that the proposed method reduces the maximum position deviation by 83–94% compared to PID, LADRC, and conventional SMC controllers under the tested disturbance conditions, achieving settling time reductions exceeding 90%. Under combined thermal drift and external loading, the proposed approach limits the maximum tracking error to below 0.45° while maintaining a steady-state error under 0.08°. Full article

Machine components are subject to a wide range of damage and failure processes, and their correct identification is essential for reliable operation, effective maintenance, and accurate diagnosis. However, a persistent gap exists between morphology-based classification systems, used in international standards, and the mechanism-based interpretations developed in tribology and mechanics. This review analyzes the evolution and current practice of damage classification for machine components, with emphasis on rolling bearings as a representative case. The study is based on a structured analysis of international standards (e.g., ISO 15243), complemented by tribological literature and manufacturers’ documentation. The review focuses on how several damage modes such as spalling, pitting, and fretting are defined, interpreted, and applied in practice. The results highlight systematic ambiguities arising from the separation between visual descriptors and underlying failure mechanisms, particularly in the case of fatigue-related surface damage. Through selected case studies, the review demonstrates how reliance on morphology alone may obscure causal interpretation and lead to inconsistent diagnosis. The study further discusses emerging trends, including digital damage atlases and artificial-intelligence-based diagnostic tools, emphasizing how inconsistencies in standardized terminology may affect their reliability. It is concluded that morphology-based standards should be regarded as complementary diagnostic tools rather than substitutes for mechanical analysis. A closer alignment between standardized terminology and mechanistic understanding is necessary to improve failure diagnosis, support engineering education, and enhance the reliability of machine components. Full article

With increasingly stringent requirements for wear resistance and reliability of functional coatings for heavily loaded friction units, a relevant challenge in materials science is to establish the relationships between the parameters of reactive pulsed magnetron sputtering and the tribo-mechanical properties of TiN/CrN multilayer systems. In this study, TiN/CrN multilayer coatings were deposited by reactive pulsed magnetron sputtering using separate titanium and chromium targets. The effect of the nitrogen flow rate (0.20–0.36 L/h) during chromium sputtering on the structure, phase composition, and mechanical and tribological properties of the coatings was investigated at a fixed nitrogen flow rate of 0.08 L/h for titanium. SEM, EDS, and XRD showed that increasing the nitrogen flow rate leads to a non-monotonic change in coating thickness (2.0–2.6 µm), caused by the transition of the chromium target from the metallic to the poisoned sputtering mode. At low N₂ flow rates, a subnitride Cr₂N phase forms in the structure, whereas at the optimal flow rate of 0.32 L/h the coating consists of stable TiN, CrN, and (Cr_0.5Ti_0.5)N phases. The coating nanohardness was 20–23 GPa and the Young’s modulus was 250–300 GPa. The best tribological performance was achieved at a nitrogen flow rate of 0.32 L/h, coefficient of friction μ ≈ 0.5 and a minimum wear rate of 1 × 10⁻⁵ mm³/(m·N), which correlates with the highest H³/E² value. It is shown that independent control of the CrN layer stoichiometry using separate targets can affect the tribo-mechanical properties of the TiN/CrN multilayer system. Full article

This review provides a comprehensive overview of high-wear-resistant metal–ceramic surface engineering technologies based on Directed Energy Deposition (DED) for high-temperature industrial applications. In high-temperature processes such as continuous hot-dip coating, critical components (e.g., rollers and sleeves) are exposed to severe wear and chemical reactions, leading to rapid degradation and frequent replacement, which results in significant economic losses. This review focuses on the fundamental characteristics of DED processes and their advantages over conventional surface modification techniques such as HVOF, PVD/CVD, and arc-based methods. Particular attention is given to the process–structure–property relationships governing coating performance, including coating thickness, bonding characteristics, and high-temperature stability. Representative material systems, particularly WC-based metal–ceramic composites (e.g., Co–WC), are systematically discussed in terms of their wear resistance and applicability under severe operating conditions. Quantitative tribological performance metrics, including wear rate and friction coefficient, are also reviewed to provide a more rigorous understanding of coating performance. The analysis highlights that DED offers unique advantages in achieving thick coatings with strong metallurgical bonding and high applicability to repair and remanufacturing of large-scale components. In addition, recent advances in DED technologies, such as closed-loop control, self-regulating effects, and data-driven process optimization, are examined to highlight emerging trends in the field. The review also identifies current technical limitations and outlines future research directions, emphasizing the need for improved process control, defect mitigation, and integration of advanced monitoring techniques. Full article