Search Results (4,801)

Plasma nitriding is an advanced method to increase the hardness and wear resistance of different metal parts with complex shapes and geometries. The modelling is an appropriate approach for better understanding and improving such technologies based on multi-physical processes. Mathematical models of the coupled electromagnetic, fluid flow, and thermal processes in vacuum chambers for the low-temperature plasma treatment of metal parts have been developed. They were solved numerically via ANSYS/CFX software for a discretized solid and gas space of a plasma nitriding chamber. The specific electrical conductivity of the gas mixture, containing plasma, has been calibrated on the basis of an electrical model of the chamber and in situ measurements. The three-dimensional fields of pressure, temperature, velocity, turbulent characteristics, electric current density, and voltage in the chamber have been simulated and analysed. Methods for further development and application of the models and for technological and constructive enhancement of the plasma treatment technologies are discussed. Full article

Hard anodic oxide coatings on aluminium have long been used to enhance surface functionality. However, increasing industrial demands are driving the need for coatings with superior hardness, wear resistance, corrosion resistance and self-lubricating properties. Due to their porous structure, anodic oxide coatings can be modified by incorporating various nanoparticles. The properties of the modified coatings depend on both the type of nanoparticles used and the method employed to incorporate them. In this study, anodic oxide coatings were produced using direct and duplex methods on a semi-industrial scale to enable process control and potential industrial implementation. The coatings were modified with hard (Al₂O₃) and soft (CaCO₃, PTFE) nanoparticles in order to customise their functional properties. Their microstructure and chemical composition were characterised by SEM and TEM. Their microhardness, abrasion resistance and electrochemical behaviour were also evaluated. Among the tested production methods and methods for modifying nanoparticles, the duplex process incorporating Al₂O₃ particles proved to be the most promising. Its optimisation resulted in coatings with a microhardness of 430 HV0.05 and a mass loss of 9.4 mg after the Taber abrasion test, demonstrating the potential of this approach for industrial applications. Full article

CeO₂ doping is a well-established strategy for enhancing the properties of zirconia (ZrO₂) ceramics, with the prior literature indicating an optimal doping range of around 10–15 wt.% for specific attributes. Building upon this foundation, this study provides a systematic investigation into the concurrent evolution of mechanical, tribological, and thermophysical properties across a broad compositional spectrum (0–20 wt.% CeO₂). The primary novelty lies in the holistic correlation of these often separately examined properties, revealing their interdependent trade-offs governed by microstructural development. The 15Ce-ZrO₂ composition, consistent with the established optimal range, achieved a synergistic balance: hardness increased by 27.6% to 310 HV₁, the friction coefficient was minimized to 0.205, and the wear rate was reduced to 1.81 × 10⁻³ mm³/(N m). Thermally, it exhibited a 72.2% reduction in the thermal expansion coefficient magnitude at 1200 °C and a low thermal conductivity of 0.612 W/(m·K). The enhancement mechanisms are consistent with solid solution strengthening, grain refinement, and likely enhanced phonon scattering, potentially from point defects such as oxygen vacancies commonly associated with aliovalent doping in oxide ceramics, while performance degradation beyond 15 wt.% is linked to CeO₂ agglomeration and duplex microstructure formation. This work provides a relatively comprehensive insight into the dataset and mechanism, which is conducive to the fine design of multifunctional ZrO₂ bulk ceramics. It is not limited to determining the optimal doping level, but also aims to clarify the comprehensive performance map, providing reference significance for the development of advanced ceramic materials with synergistically optimized hardness, wear resistance, and thermal properties. Full article

This study aimed to experimentally investigate the differences in metallic structures owing to the gas nitriding and quenching process (GNQP) temperature of the Ti-15mass%Nb alloy and differences in the tribological properties of the surface layer. The GNQP heating temperature was 1023 K or 1223 K, and the holding time was set to 1 h. In the X-ray diffraction profiles, the diffraction peak of the (10$\overline{1}$1) plane of the hexagonal close-packed phase exhibited a shift toward lower angles, following the sequence AN:α, AQ:α′, and GNQP:α-TiN_0.3. In both the 1023 K and 1223 K GNQP specimens, the α″ phase exhibited lower values than the α′ phase; nonetheless, it still exhibited larger values than the annealed α phase. Based on transmission electron microscopy observations, the high core hardness of the 1223 K GNQP specimen was attributed to solid-solution strengthening caused by nitrogen diffusion or to strain hardening associated with the diffusion and was not attributed to the influence of precipitation phases, such as the ω phase. In the friction and wear tests, both the 1023 K and 1223 K GNQP specimens exhibited narrower wear track widths, clearly demonstrating that the GNQP enhanced the wear resistance. Moreover, the TiO₂ layer was effective in maintaining a low coefficient of friction. Full article

Friction Stir Processing (FSP) has emerged as an advanced solid-state surface engineering technique for tailoring high-performance surface architectures in metal matrix composites (MMCs). By combining localized thermo-mechanical deformation with controlled material flow, FSP enables grain refinement, homogeneous dispersion of reinforcement, and strong interfacial bonding without melting or altering bulk properties. This review critically examines the role of FSP in enhancing the mechanical, tribological, and corrosion performance of composites, with emphasis on process–structure–property relationships. Key strengthening mechanisms, including grain boundary strengthening, load transfer, particle pinning, and defect elimination, are systematically discussed, along with their implications for wear resistance, fatigue life, and durability. Special attention is given to corrosion and tribo-corrosion behavior, highlighting electrochemical mechanisms such as micro-galvanic interactions, passive film stability, and interfacial chemistry. Furthermore, the eco-efficiency, industrial viability, and sustainability advantages of FSP are evaluated in comparison with conventional surface modification techniques. The review concludes by identifying critical challenges and outlining future research directions for the scalable, multifunctional, and sustainable design of composite surfaces. Full article

Metal–organic frameworks (MOFs) and porous organic frameworks (POFs) have been extensively explored in recent years as lubricant additives for various systems due to their structural designability, pore storage capacity, and tunable surface chemistry. These materials are utilized to construct low-friction, low-wear interfaces and investigate the potential for superlubricity. This paper systematically reviews the tribological behavior and key mechanisms of MOFs/POFs in oil-based, water-based, and solid coating systems. In oil-based systems, MOFs/POFs primarily achieve friction reduction and wear resistance through third-body particles, layer slip, and synergistic friction-induced chemical/physical transfer films. However, limitations in achieving superlubricity stem from the multi-component heterogeneity of boundary films and the dynamic evolution of shear planes. In water-based systems, MOFs/POFs leverage hydrophilic functional groups to induce hydration layers, promote polymer thickening, and soften gels through interfacial anchoring. Under specific conditions, a few cases exhibit superlubricity with coefficients of friction entering the 10⁻³ range. In solid coating systems, two-dimensional MOFs/COFs with controllable orientation leverage interlayer weak interactions and incommensurate interfaces to reduce potential barriers, achieving structural superlubricity at the 10⁻³–10⁻⁴ level on the micro- and nano-scales. However, at the engineering scale, factors such as roughness, contamination, and discontinuities in the lubricating film still constrain performance, leading to amplified energy dissipation and degradation. Finally, this paper discusses key challenges in achieving superlubricity with MOFs/POFs and proposes future research directions, including the design of shear-plane structures. Full article

Background: Composite restorations are the standard of care for posterior teeth due to their aesthetic properties and conservative nature. However, the choice between direct and semi-direct techniques can influence clinical longevity and performance. Objectives: This study aimed to compare the clinical performance of two restorative approaches: a direct technique and the semi-direct onlay technique in terms of aesthetic quality, surface finish, wear resistance, marginal integrity, and overall clinical efficiency over a two-year period. Methods: A total of 348 composite restorations were placed in 192 patients. Each restoration was evaluated at four timepoints: baseline (T0), 6 months (T1), 1 year (T2), and 2 years (T3). Clinical performance was assessed using standardised 5-point rating scales across the five dimensions. Repeated-measures ANOVA assessed changes over time, while Wilcoxon signed-rank and Mann–Whitney U tests were used for intra- and inter-group comparisons. Results: Significant time effects were observed across all clinical parameters (p < 0.0001). The direct technique exhibited superior initial results in aesthetics and surface finish at T0 and T1 (p < 0.001), but differences diminished by T3. In contrast, the semi-direct technique demonstrated improved performance in wear resistance and marginal integrity at T2 and T3. Both techniques showed progressive deterioration, particularly in marginal adaptation. Conclusions: The direct technique offers enhanced short-term aesthetics and procedural efficiency, while the semi-direct approach provides superior long-term durability and marginal adaptation. Full article

Vulcanized NR-SBR is widely used in vehicle components; however, its irreversible crosslinking limits recyclability and contributes to the large number of tires discarded annually worldwide, and in this context, this work presents an experimental comparative assessment of the tribological behavior of conventional tire rubber and silicone VMQ, motivated by a wheel concept based on a detachable tread aimed at improving durability and sustainability rather than proposing an immediate material substitution. Wear and friction behavior were investigated under abrasive and self-friction conditions using pin-on-disk testing with an abrasive counterpart representative of asphalt, supported by optical and scanning electron microscopy. The results show that NR-SBR undergoes severe abrasive and erosive wear, characterized by deep and irregular wear tracks, pronounced fluctuations in the dynamic friction coefficient, and strong sensitivity to load and sliding speed, particularly during the initial stages of track formation. In contrast, VMQ exhibits mild abrasive wear dominated by viscoelastic deformation, leading to shallow and stable wear tracks, lower friction coefficients, and significantly reduced material loss once the contact track is fully developed. These differences are attributed to the distinct mechanical responses of the elastomers, as the higher hardness and limited strain capacity of rubber promote micro-tearing and unstable material removal, while the high elasticity of silicone enables stress redistribution and stable contact conditions under abrasive loading. UV aging increases stiffness of rubber, resulting in reduced wear and friction, while silicone remains largely unaffected after 750 h due to the stability of its Si–O–Si backbone. Self-friction tests further indicate that smooth silicone sliding against rubber yields the lowest friction values, highlighting a favorable material pairing for detachable tread concepts. Factorial design analysis confirms material type as the dominant factor influencing both wear and friction. Overall, for the specific materials and operating conditions investigated, VMQ demonstrates higher durability, greater tribological stability, and improved aging resistance compared to NR-SBR, providing experimental evidence that supports its potential for long-life, more sustainable detachable tread applications. Full article

Energy conservation and efficiency enhancement necessitate continuous advancement in the development and preparation of multifunctional, high-performance lubricant additives. This paper reports three novel ashless, phosphorus-free, multifunctional nitrogen-containing heterocyclic dialkyl dithiocarbamate derivative additives (Py-2-DBDTC, PDM-DBDTC, and BZT-DBDTC). Thermal stability, oxidation resistance, and tribological properties were investigated for the synthesized additives. All three additives demonstrated excellent thermal stability and oxidation resistance. Furthermore, their extreme-pressure properties improved by 116.33% or more compared to the base oil, while wear reduction rates also exceeded 58.32%. Under both point-to-point and point-on-flat friction conditions, the friction-reducing performance of all three additives was equally outstanding. Across a broad temperature range (25 °C–150 °C), all additives maintained their friction-reducing properties. Analysis of the worn surface morphology reveals that all three additives undergo tribochemical reactions during the friction process, forming tribofilms containing sulfur elements. Research indicates that introducing different nitrogen-containing heterocyclic structures into dialkyl dithiocarbamates can effectively enhance the adsorption capacity of the additives on metal surfaces and promote the formation of tribofilms at the friction interface, thereby significantly improving tribological performance. These systematic investigations not only provide important guidance for the molecular design and industrial application of multifunctional lubricant additives but also further advance the development of sustainable lubrication technologies. Full article

To address the severe wear of the hole wall and orifice in ejector pin guide holes of injection molds caused by frequent hole-shaft sliding, this study proposes a composite strengthening method that combines nitriding with oblique laser shock peening (N-OLSP). The strengthening uniformity in both circumferential and axial directions was evaluated by defining a laser shock peening uniformity coefficient ($k$). By strictly controlling the uniformity coefficient ratio of two adjacent spots to be no less than 0.98, the optimal step angles for circumferential and axial directions were determined. Comparative experiments were conducted on three types of samples: Untreated, Nitrided, and N-OLSP treated. The results demonstrate that N-OLSP significantly enhances both surface hardness and residual compressive stress of the guide hole, and the degree of improvement increases with a higher value of $k$. Among the tested samples, N-OLSP exhibited the best wear resistance at the orifice, reducing the wear rate to 0.60 μm/h. Compared with the untreated and nitrided samples, the wear rate reduction achieved by N-OLSP was 66.85% and 16.67%, respectively. Full article

The operating conditions of engines in motor vehicles used in conditions of high air dustiness resulting from sandy ground and helicopters using temporary landing sites were analyzed. The impact of mineral dust on accelerated abrasive and erosive wear of components and assemblies of piston and turbine engines was presented. Attention was drawn to the formation of dust deposits on turbine engine components. Possibilities for minimizing abrasive wear through the use of two-stage intake air filtration systems in motor vehicle engines were presented. Three forms of protection for helicopter engines against the intake of dust-laden air and for extending their service life are presented: intake barrier filters (IBF), tube separators (VTS), and particulate separators (IPS) called Engine Air Particle Separation (EAPS). It has been shown that pleating the filter bed significantly increases the filtration area. It has been shown that increasing the suction flow from inertial filters increases separation efficiency and flow resistance. IPS are characterized by a compact design, low external resistance, and no need for periodic maintenance, but it has a lower separation efficiency (86–91%) than VTS and IBF systems (up to 99.3–99.9%). The tested “cyclone-partition filter” filtration system achieves a filtration efficiency of 99.9%, reaching the acceptable pressure drop value four times slower than if it were operating without a cyclone. Two-stage filtration systems ensure high friction durability at the lowest possible energy costs. Full article

Niobium nitride (δ-NbN) coatings were deposited on AISI 316L austenitic steel using reactive DC magnetron sputtering. This study investigates the effects of air oxidation on the surface morphology, topography, roughness, nanohardness, adhesion, and wear resistance of NbN coatings. Their microstructure and thickness were analyzed by scanning electron microscopy (SEM), while surface morphology and roughness were assessed using atomic force microscopy (AFM), and surface topography was assessed by an optical profilometer. Nanohardness was measured using a Berkovich indenter. Adhesion was evaluated via progressive-load scratch testing and Rockwell indentation (VDI 3198 standard). Wear resistance was assessed using the “ball-on-disk” method. Both as-deposited and oxidized NbN coatings improved the mechanical performance of the substrate surface. Air oxidation led to the formation of an orthorhombic Nb₂O₅ surface layer, which increased surface roughness and reduced hardness. However, the brittle oxide also contributed to a lower coefficient of friction. Despite reduced adhesion and increased surface development, the oxidized coating exhibited a significantly lower wear rate than the uncoated steel, though several times higher than that of the non-oxidized NbN. Considering its good wear and corrosion performance, along with the bioactivity confirmed in earlier research, the oxidized NbN coating can be considered a promising candidate for biomedical applications. Full article

Micro-arc oxidation (MAO) coatings were produced on commercially pure titanium Grade 2 using a composite electrolyte containing sodium phosphate (Na₃PO₄) and sodium silicate (Na₂SiO₃), while varying the applied voltage. The surface morphology, phase composition, and structural features of the coatings were examined using scanning electron microscopy (SEM) and X-ray diffraction (XRD). The coatings exhibited a characteristic crater-like microporous surface morphology associated with the micro-arc discharge process. XRD analysis confirmed the formation of mixed TiO₂ phases in the anatase and rutile modifications, with higher voltages promoting the growth of the thermodynamically stable rutile phase. Corrosion and tribological properties were evaluated in a 3.5 wt.% NaCl solution using potentiodynamic polarization and a ball-on-disc test configuration, respectively. The results revealed a substantial improvement in both corrosion resistance and wear performance compared with bare titanium. The coating formed at 300 V demonstrated the highest wear resistance due to its denser microstructure, whereas the coating produced at 350 V exhibited the lowest friction coefficient and the greatest corrosion resistance, attributed to the increased rutile content. Overall, MAO coatings fabricated in the phosphate–silicate electrolyte effectively enhance the combined operational properties of titanium and can be recommended for applications requiring improved wear and corrosion resistance. Full article

Regenerative hardfacing of steel substrates is an important technology for restoring the surface layer of components operating under wear conditions, supporting the goals of the circular economy (CE) by extending the service life of components, reducing material and energy consumption throughout their life cycle, and shortening downtime during machine repairs. The article provides a synthetic analysis of the literature on the production of functional layers exclusively on steels and systematizes process → structure → properties (PSP) relationships in the context of technological quality and the prediction of the functional properties of welds. The review covers methods used and developed in steel hardfacing (including arc processes and variants with increased energy concentration), analyzed on the basis of measurable process indicators: energy parameters (arc energy/heat input/volume energy), dilution, bead geometry, heat-affected zone characteristics, and the risk of welding defects. It has been shown that these factors determine the structural effects in the weld and the area at the fusion boundary (including phase composition and morphology, hardness gradient, and susceptibility to cracking), which translates into functional properties (hardness, wear resistance, adhesion, and fatigue life) and durability after regeneration. The main result of the work is the development of a PSP table dedicated to hardfacing on steel substrates, mapping the key “levers” of the process to structural consequences and trends in functional properties. This facilitates the identification of optimization directions (minimization of energy input and dilution while ensuring fusion continuity), which translates into longer durability after regeneration and a lower risk of defects—key, measurable effects of CE. Research gaps have also been identified regarding the comparability of results (standardization of energy metrics) and the need to determine and verify “technology windows” within the WPS/WPQR (welding procedure specification/welding procedure qualification record) for layers deposited on steels. Full article

The milled surface topography of NiTi SMA critically affects its frictional behavior, corrosion resistance, and biocompatibility, which are essential for biomedical and aerospace applications. This study combines simulation and single-factor experiments to investigate the coupling behavior among surface topography evolution, work hardening, plastic deformation, and residual stress evolution. Results showed that increasing feed per tooth led to a significant rise in surface residual height and an improvement in surface isotropy. With the increase in feed per tooth, the error between the experimental and simulated heights gradually decreased from 105.6% to 30.9%, indicating that both material properties and feed per tooth strongly affect residual profile formation in the feed direction. In addition, larger feed per tooth intensifies work hardening and plastic deformation but reduces surface residual stress, thereby increasing microhardness. These effects can mitigate material rebound and improve surface profile accuracy. The results provide a direct basis for controlling the surface integrity of NiTi SMA components through machining parameter optimization, enabling precise tailoring of functional surface characteristics, such as wear performance, chemical stability, and biological response, which is of critical importance for high-end biomedical implants and aerospace systems. Full article