Search Results (2,748)

In this study, to further improve the performance of micro-arc oxidation (MAO) coatings, ZrO₂ nanoparticles at different concentrations were added to the electrolyte. The effects of ZrO₂ concentration on the microstructure, mechanical properties and corrosion resistance of the MAO composite coatings were systematically investigated. The coatings mainly consisted of α-Al₂O₃ and γ-Al₂O₃. The detection of ZrO₂ confirmed the incorporation of the added particles. As the concentration increased from 0 to 6 g/L, the porosity decreased from 1.352% to 0.864%, whereas further addition increased the porosity. At 6 g/L, the mean microhardness reached 623 ± 50 HV_0.05. Moreover, this coating showed the lowest friction coefficient of 0.135. In addition, its corrosion potential was −0.148 V, while its corrosion current density was 2.578 × 10⁻⁷ A·cm⁻². It also exhibited the highest low-frequency impedance modulus. When the ZrO₂ concentration was further increased, the coating porosity increased and the improvements gradually weakened. Overall, a suitable ZrO₂ concentration promoted coating growth and reduced structural defects. It also improved the hardness, wear behavior and corrosion protection of the coating. Therefore, these findings provide a reference for the concentration design of ZrO₂-modified MAO coatings. They also clarify the nonmonotonic relationship between coating growth, structural defects and performance. Full article

Polyurethane (PU) foams are widely used in footwear midsoles because their cellular structure, density, impact-attenuation capability, and mechanical durability can be tailored through formulation design. In this study, polyester-based PU foams were prepared at different isocyanate indices while keeping the main formulation components constant, and their structure-property relationships were evaluated under midsole-relevant conditions. The samples were characterized by density, tensile and compression testing, standard abrasion wear testing, water absorption, temperature-dependent flexural resistance, Fourier transform infrared (FTIR), scanning electron microscope (SEM), differential scanning calorimetry (DSC), thermogravimetric analysis/derivative thermogravimetry (TGA/DTG), and dry/wet tribometry. FTIR results confirmed the formation of urethane/urea-related linkages and the absence of detectable residual isocyanate groups, whereas DSC indicated broad heat-flow events typical of segmented PU systems, including high-temperature events that should be interpreted together with TGA. TGA/DTG analysis showed similar initial degradation behavior for all formulations; however, the 138-index sample exhibited the highest t_90% value, indicating improved high-temperature mass retention. Tribometric tests revealed an environment-dependent coefficient of friction (COF) response: the 138-index sample exhibited the lowest steady-state COF under dry sliding (μ_ss = 0.211), whereas the 113-index sample showed the lowest COF value under wet sliding conditions (μ_ss = 0.176). Overall, among the three stable formulations investigated, the 113-index formulation exhibited the most balanced multi-property performance. These results suggest that, within the tested formulation range, midsole-relevant PU foam performance is associated with a balance of formulation characteristics rather than simply with increasing the isocyanate index. Full article

Ti-6Al-4V alloy exhibits excellent comprehensive mechanical properties and good corrosion resistance; however, its relatively low surface hardness and insufficient wear resistance limit its further applications in sliding contact and corrosive environments. In this study, plasma nitriding at 750 °C was employed to modify the surface of Ti-6Al-4V alloy, and the effects of plasma nitriding treatment on microstructural evolution, wear resistance, and electrochemical corrosion behavior were systematically investigated. The results indicate that a continuous nitrided layer with a thickness of approximately 2.77 µm was formed on the surface of Ti-6Al-4V alloy. The surface hardness increased from 317.60 HV for the untreated sample to 548.77 HV after plasma nitriding. Compared with the untreated sample, the average friction coefficient of the nitrided sample increased from 0.328 to 0.497; however, the maximum wear depth decreased significantly from 73.91 µm to 0.60 µm, and the wear rate decreased from 30.73 × 10⁻⁵ mm³·N⁻¹·m⁻¹ to 0.43 × 10⁻⁵ mm³·N⁻¹·m⁻¹, corresponding to a reduction of approximately 98.6%. Wear morphology analysis shows that severe ploughing grooves, adhesive tearing, and localized spalling dominated the wear mechanism of the untreated sample. In contrast, the nitrided sample exhibited significantly mitigated wear, characterized mainly by shallow grooves, slight debris accumulation, and minor localized delamination. Electrochemical measurements demonstrate that the nitrided sample exhibits a lower corrosion current density and higher impedance in NaCl solution, indicating that the nitrided layer effectively enhances the electrochemical stability of Ti-6Al-4V alloy. The improved wear and corrosion resistance of the plasma nitrided samples can be primarily attributed to the high hardness and effective surface protection provided by the continuous nitrided layer. Full article

This study investigates the influence of detonation spraying parameters on the microstructure, mechanical properties and tribological performance of self-fluxing Ni–Cr–Fe–Si–B–C coatings deposited on AISI 321 stainless steel substrates. The effects of the barrel filling ratio (48–68%), the oxygen-to-fuel molar ratio (O/C = 1.026–1.856), and the delay time between detonation shots (0–1 s) were systematically evaluated. The coatings were characterized using scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), X-ray diffraction (XRD), microhardness measurements, instrumented indentation, and ball-on-disk tribological testing. Microstructural investigations revealed that the spraying parameters significantly influence coating thickness, porosity and defect formation. The lowest porosity (0.306 per cent) and the most homogeneous microstructure were obtained at a barrel filling ratio of 48 per cent, an O/C ratio of 1.026 and a shot delay of 1 s. XRD analysis identified a multiphase structure consisting of a Ni₃Fe matrix reinforced by Cr₇C₃ carbides, Ni₃B and CrB borides, and Ni₃₁Si₁₂ silicides. Tribological tests demonstrated that increasing the delay between shots significantly improved wear resistance, reducing the wear rate to 1.89 × 10⁻⁴ mm³/(N × m). The optimised coating exhibited an average coefficient of friction of 0.578 ± 0.093 and a wear rate of 1.03 × 10⁻⁴ mm³/(N × m). Instrumented indentation revealed a hardness of 1049.1 ± 43.4 HV and a Young’s modulus of 215.9 ± 8.5 GPa. The wear mechanism was predominantly abrasive–adhesive, whilst the wear rate of the 100Cr6 counter-body remained low at 1.20 × 10⁻⁵ mm³/(N × m). The results obtained demonstrate that appropriate optimisation of detonation spraying parameters enables the formation of dense Ni–Cr–Fe–B–Si–C coatings with superior mechanical and tribological properties, making them promising candidates for wear-resistant engineering applications. Full article

Metallic powder systems containing niobium play a key role in the development of advanced materials for structural, biomedical, energy, and surface-engineering applications. The incorporation of niobium into metallic powders influences particle behavior during processing, phase stability, microstructural evolution, and the resulting mechanical and corrosion properties of consolidated materials. This review examines the scientific and technological advances related to niobium-containing metallic powders, covering powder production routes, particle characterization methods, processing techniques, and performance evaluation. Publications on powder metallurgy, additive manufacturing, thermal processing, surface modification, and corrosion-resistant materials were analyzed to identify relationships among powder characteristics, processing conditions, and material performance. The available evidence indicates that niobium contributes to grain refinement, precipitation control, microstructural stabilization, improved resistance to wear, and localized corrosion. The element also expands the applicability of metallic powders in functional coatings, biomaterials, engineered surfaces, and components manufactured from particulate feedstocks. Current challenges involve powder homogeneity, process reproducibility, economic considerations, and the prediction of long-term service behavior. The analysis highlights niobium’s contribution to the design of high-performance metallic powder systems and identifies research directions for developing materials with enhanced reliability and industrial applicability. Full article

High-entropy carbide (HEC) coatings have emerged as promising candidates for extreme tribological and high-temperature applications; therefore, the objective of this work is to systematically investigate the correlation between carbon stoichiometry and the microstructural evolution, mechanical response, and thermal stability of (TiAlTaZrNb)Cx high-entropy carbide coatings. Here, HEC coatings were synthesized via reactive unbalanced-field pulsed-bias magnetron sputtering, with methane flow rates precisely tuned to yield carbon concentrations ranging from 24 to 55 at.%. XRD and Raman analyses reveal a transition from a dense, columnar FCC NaCl-type solid solution with a (200) preferential orientation to a (111)-textured matrix containing secondary carbides (TiC, TaC) and sp²-bonded free carbon at elevated carbon levels. Nanohardness and elastic modulus reach an optimal plateau at ~35 at.% C (29 GPa and 350 GPa, respectively), followed by a decline to ~20 GPa and 223 GPa at 55 at.% C due to the percolation of soft carbon-rich phases. Remarkably, increasing carbon content drastically enhances tribological performance: the coefficient of friction decreases from 0.40 to 0.20, and the specific wear rate drops from 35 × 10⁻⁶ to 1.7 × 10⁻⁶ mm³/(N·m), consistent with a solid-lubrication mechanism inferred from as-deposited Raman trends and wear-track compositional analysis, though direct post-wear spectroscopic validation remains a priority for future work. Thermal stability assessments at 600 °C at an intermediate low pressure demonstrate excellent microstructural and mechanical retention for low-to-intermediate carbon compositions, with oxidation confined to a ~200 nm surface layer attributed to the formation of stable titanium and tantalum oxides and oxycarbides, which possibly forms an oxygen diffusion barrier at that temperature. An optimal carbon content of ~35 at.% C delivers a superior synergy of high hardness, exceptional wear resistance, and robust thermal stability, establishing (TiAlTaZrNb)Cx as a highly tunable coating system for next-generation protective applications. This work provides the first systematic composition–performance map for this quinary HEC system across a broad stoichiometric range, demonstrating that carbon stoichiometry serves as a master variable to tailor the balance between mechanical integrity and tribological functionality. Full article

The nanoscale surface topography and microhardness of additive and subtractive dental polymers were evaluated following exposure to environmental challenges. The study examined two 3D-printed resins (Saremco and Voco) and two milled CAD/CAM blocks (Vita Enamic and Tetric). Specimens were allocated to control or experimental groups and subjected to hydrothermal ageing (thermocycling), in vitro mechanical wear, or a combined protocol involving wear followed by thermal ageing. Surface microtopography was analysed both quantitatively and qualitatively using atomic force microscopy (AFM), while structural stability was assessed through surface microhardness testing. Statistical significance was determined using matrix comparisons (p < 0.05). Milled monolithic blocks demonstrated a dense, uniform baseline topography, whereas 3D-printed resins exhibited structural heterogeneity attributed to their layer-by-layer photocuring process. Saremco maintained polymer network stability under thermal stress (p = 0.1878), while Voco was highly susceptible to hydrothermal swelling and early matrix plasticization (p = 0.0084). The combined protocol of wear and thermal ageing resulted in advanced structural breakdown in all groups (p < 0.001). Industrial subtractive blocks exhibited greater resistance to oral environmental stresses. The ceramic framework of Vita Enamic limited polymer domain collapse, whereas Tetric experienced accelerated inter-layer delamination and embrittlement. The combined protocol of wear followed by thermal ageing resulted in significant and uniform degradation of surface microhardness and topographic roughness in all tested groups. Nevertheless, the additively manufactured resins demonstrated substantial structural integrity and exhibited low volumetric wear rates. Full article

To realize the remanufacturing of cast iron components, a WC-reinforced Fe-based composite powder was designed, and the WC/Fe-based composite coating was deposited on the HT250 substrate by laser cladding. The melting and dissolution mechanism of WC ceramic particles were investigated, and their influences on the microstructure, phase, microhardness, and wear resistance of the composite coatings were systematically analyzed. The results show that the WC/Fe-based composite coating achieves good metallurgical bonding with the HT250 substrate and possesses excellent forming quality. The incorporated WC particles can effectively optimize the microstructural morphology, acting as heterogeneous nucleation sites and inhibiting grain growth. As WC content increases, the grain size within the composite coating gradually refines. Moreover, partially melted WC particles release tungsten (W) and carbon (C) elements into the molten pool, promoting the in-situ generation of new hard phases, including W₂C and Fe₆W₆C. These newly formed phases, together with the residual unmelted WC particles, contribute a dispersion strengthening effect and improve the properties of the composite coatings. This effect becomes more pronounced with higher WC content. Notably, the composite coating with 20% WC exhibits a microhardness over twice that of the HT250 substrate, while its wear rate is only one-sixth that of the substrate and its corrosion resistance is much higher than that of the HT250 substrate. Full article

Magnesium alloys are used or considered for lightweight structures and biodegradable implants, but high electrochemical activity, limited wear resistance, and localized corrosion still limit their service reliability. Plasma electrolytic oxidation (PEO), also called micro-arc oxidation (MAO), forms an adherent ceramic scaffold. Discharge channels, interconnected pores, thermal cracks, and a mechanically weak outer layer mean that the as-formed coating is rarely a complete protective system. This review examines advanced PEO/MAO-based composite coatings through a process–structure–function lens and develops an application-oriented design framework. The discussion covers PEO/MAO process-window control, electrolyte and particle engineering, sol–gel and polymer sealing, layered double hydroxide/inhibitor systems, self-healing reservoirs, superhydrophobic and slippery interfaces, Ca-P/hydroxyapatite and polymer biofunctionalization, and duplex coatings for wear, electrical, and thermal functions. Emphasis is placed on how these modules regulate defect connectivity, mass transport, interfacial stability, damage response, tribocorrosion, and biodegradation, as well as on the evidence needed to support each claimed function. The analysis indicates that coating performance is governed not by multilayer complexity alone, but by the compatibility among the ceramic scaffold, functional module, dominant failure mode, and service-specific validation protocol. Chloride-exposed structures require durable pore sealing and active inhibition; wear-critical components require coupled corrosion–wear assessment; and biodegradable implants require a degradation window that balances corrosion moderation, cytocompatibility, biofunctionality, and residual mechanical integrity. Remaining challenges include interfacial durability, finite inhibitor reservoirs, wetting-state instability, process reproducibility, scale-up, and life-cycle impacts. The proposed process maps and validation criteria are intended to support modular, testable, and application-specific PEO/MAO surface systems for magnesium alloys. Full article

Conventional pavement design methods are generally intended for highways and are not suited to the extreme loading conditions experienced by mining haul roads. This study presents an innovative pavement design for a heavily trafficked phosphate mine haul road (≈22.35 kT·day⁻¹) constructed entirely from phosphate mine waste rock (PMWR), offering a sustainable alternative to conventional aggregates. The proposed structure comprises a 0.35 m sub-base (0–100 mm), a 0.25 m base (0–63 mm), and a 0.07 m semi-granular asphalt concrete (BBSG 0–20 mm) wearing course designed to combine high mechanical performance with effective dust control. The design was validated through an integrated experimental program that included repeated load triaxial testing (RLTT), asphalt stiffness, fatigue and rutting tests, thermogravimetric analysis (TGA), and full-scale field trials involving EV₂ plate-load testing, dust monitoring, and emergency braking tests using a Komatsu 730E haul truck. The results demonstrate that the proposed pavement provides excellent structural performance. The asphalt mixture achieved a stiffness modulus of 9160 MPa, a fatigue resistance of 139.6 µε, and a proportional rut depth (PRD) of only 2.2%. In the field, the compacted sub-base and base reached average EV₂ values of 153 MPa and 181 MPa, respectively, confirming their high load-bearing capacity. The paved haul road reduced airborne dust emissions by approximately 91%, surpassing the mine’s target of 80%, while also enabling haul-truck operating speeds to double, with associated reductions in tire wear and maintenance. Despite these performance gains, the proposed solution remains economically attractive, with a construction cost of approximately 23.97 €/m². Overall, the study demonstrates that phosphate mine waste rock can be successfully transformed into a durable, cost-effective, and environmentally sustainable pavement solution for heavy-haul mining roads, providing a practical example of circular economy principles in mining infrastructure. Full article

In this work, CrAlN thin films were used to improve the lifespan of cutting tools. The CrAlN thin films were deposited on X50CrMoV8 substrates and silicon using DC reactive magnetron sputtering. The influence of substrate rotation speed (varied between 0.5 and 3 rpm) on the morphology, mechanical properties, and tribological properties of the thin films was investigated. The results showed that this process parameter had no significant influence on chemical composition or morphology. Nevertheless, the mechanical properties were enhanced. Specifically, CrAlN hardness increased significantly with the rise in substrate rotation speed from 0.5 to 1.5 rpm. Additionally, the adhesion strength of CrAlN coatings followed the same trend as hardness. When the substrate rotation speed increased, the residual stress shifted from tensile to compressive. Changing the rotation speed did not affect the friction coefficient value but did impact wear resistance. Thin films deposited at 0.5 and 1 rpm exhibited the lowest wear resistance. Once the rotation speed increased, wear behavior improved significantly. The CrAlN thin film deposited at a substrate rotation speed of 1.5 rpm showed the best wear resistance along with the highest hardness and adhesion strength. Full article

This study investigates the design, microstructure, and performance profile of a novel composite coating combining a high-entropy alloy (HEA) matrix with cermet reinforcement. A 50wt.%CoCrFeMnNi_0.8V–50wt.% Cr₃C₂-Ni₈₀Cr₂₀ powder mixture was successfully deposited onto steel substrates via high-velocity oxy-fuel (HVOF) thermal spraying. Microstructural analysis revealed a highly dense, well-bonded coating architecture (450–500 μm thick) where partially melted, spherical HEA splats were uniformly surrounded by the Cr₃C₂-Ni₈₀Cr₂₀ phase. X-ray diffraction confirmed a complex multiphase evolution consisting of FCC, BCC, and σ-NiCr phases driven by the rapid solidification inherent to the HVOF process. Tribological evaluations via ball-on-disc testing demonstrated that incorporating the Cr₃C₂-Ni₈₀Cr₂₀ reinforcement significantly improves wear resistance compared to the monolithic HEA coating. The composite’s wear behavior is governed by a synergistic mechanism: the ductile HEA matrix accommodates plastic deformation, while the harder carbide particles enhance load-bearing capacity, transitioning from adhesive wear to mild third-body abrasion and protective tribo-oxidation. Conversely, electrochemical testing in a 3.5 wt.% NaCl solution showed that the composite coating exhibits higher corrosion current densities (10.53 × 10⁻⁶ A/cm²) and more active corrosion potentials than the pure HEA matrix. This behavior is attributed to localized micro-galvanic cells forming at the heterogeneous interfaces between the different phases, alongside chloride-induced destabilization of the surface oxide film. Overall, the novel composite coating offers a compelling, sustainable alternative for surface engineering applications requiring a balanced trade-off between mechanical toughness and acceptable environmental durability. This behavior is also verified by the comparison with previous results dealing with monolithic CoCrFeMnNi_0.8V and 75wt.%CoCrFeMnNi_0.8V–25wt.% Cr₃C₂-Ni₈₀Cr₂₀ thermal sprayed coatings, where it is evident that the increase of the reinforcing phase leads to an optimum combination of properties. Full article

Cu-Sn-Ti metallic-bonded CBN (Cubic Boron Nitride) abrasives are widely applied in the precision grinding of superhard materials. However, their high density and high toughness easily lead to poor grain protrusion and inadequate self-sharpening. In this work, ceramic glass powder was incorporated to modify the Cu-Sn-Ti binder, thereby fabricating composite-bonded CBN abrasive blocks with qualified mechanical properties and excellent self-sharpening performance. Flexural strength of abrasive blocks and microhardness of composite binders were measured; microstructure was characterized, phase composition was analyzed by XRD, and tribological tests were carried out between CBN blocks and silicon nitride abrasives. The results indicate that at glass powder contents of 2.94–10.22 wt%, the flexural strength of CBN blocks decreases by 32.5–89.4%, and binder microhardness reduces by 26.5–58.3%. At high brazing temperature, Ti and Cu from Cu-Sn-Ti alloy react with Si and Al in glass powder at the interface to form new phases including Ti₂O₃, Ti₅Si₃ and Ti(Cu,Al)₂, which facilitates favorable interfacial bonding among the alloy matrix, glass phase and CBN grains. With increasing glass powder content, the strength decline gradually slows down. The overall wear resistance of abrasive blocks declines. SEM observations on worn CBN blocks and their composite binders reveal the formation of micropores within glass-containing binders, accompanied by a shift in the fracture mode of CBN abrasives upon glass powder addition. Comprehensive experimental analysis indicates that the No.3 sample with 8.33 wt% glass powder possesses the optimal overall performance. Full article

Marine deck coatings suffer from premature failures such as wear thinning, flaking, and brittle cracking under repeated rolling, abrupt stopping/steering, and high shear loads of heavy equipment due to the imbalance of hardness, strength, toughness, and wear resistance. To address this issue, a rolling load-resistant coating system with an epoxy–amine/epoxy–thiol dual-crosslinked network was constructed using liquid polysulfide rubber (Lp-3) as the key crosslinking modifier, and the effect of Lp-3 content (0–2 wt%) on the comprehensive performance of the coating was systematically investigated. The results showed that the coating achieved the optimal synergy of properties at 1 wt% Lp-3 loading: Shore hardness reached 88.7 HD with the pencil hardness maintained at 8H, adhesion strength increased to 7.2 MPa, Taber abrasion loss significantly decreased to 14.8 mg, tensile strength rose from 5.5 MPa to 12.4 MPa, elongation at break nearly doubled, shear strength reached 10.2 MPa, and the failure mode transformed from brittle cleavage to ductile shear. Mechanistic analysis revealed that the terminal thiol groups of Lp-3 underwent a click reaction with epoxy groups, covalently embedding flexible polysulfide segments into the rigid epoxy network and forming Fe–S interfacial chemical bonds to enhance adhesion. The microphase separation, chain relaxation, and energy dissipation mechanisms effectively blunted crack propagation and alleviated stress concentration, while maintaining sufficient surface hardness and the continuity of the load-bearing skeleton. This work realizes the synergistic optimization of high strength, high toughness, strong adhesion, and excellent wear resistance for marine deck coatings and provides a new strategy and critical technical parameters for the design of functional coatings under heavy-duty dynamic service environments. Full article

Background: In the field of minimally invasive restorative dentistry, ultrathin (<0.5 mm thickness) ceramic occlusal veneers are increasing being used as alternatives to full-coverage crowns, particularly for mild occlusal wear and not deep caries. However, only limited research attention has been given to how marked reduction in the thickness of a veneer restoration affects its mechanical performance. The purpose of the present in vitro study was to compare the performance of restorations that comprised a 0.3 mm thick zirconia veneer to the case when a lithium disilicate veneer was used, under quasi-static compressive loading. Methods: Forty extracted human molars, without caries, cracks or fractures and with intact coronal structure, were randomly assigned to two groups: lithium disilicate occlusal veneers (n = 20) and zirconia occlusal veneers (n = 20). The teeth were embedded in acrylic resin up to the cementoenamel junction. Digital scans were used to record the original anatomy and guide restoration design. Standardized occlusal preparations were performed using a 0.3 mm reduction protocol and verified with silicone guides to support a biomimetic, tooth-preserving approach. After preparation, the teeth were rescanned, and restorations were designed and fabricated using CAD/CAM technology. Lithium disilicate restorations were milled from Ivoclar Porcelain System [IPS], esthetic maximized [e.max] computer-aided design [CAD] blocks, whereas zirconia restorations were milled from Prettau 3 zirconia discs. Restorations were adhesively cemented with dual-cure resin cement following material-specific surface treatment protocols. Fracture resistance was tested using a universal testing machine under compressive loading until failure. Results: The fracture loads with lithium disilicate and zirconia occlusal veneers were 481.45 ± 68.23 N and 720.93 ± 95.44 N, respectively. Fracture was catastrophic in lithium disilicate occlusal veneers whereas it was not so when zirconia veneer was used. Conclusion: Quasi-static compressive fracture load when a lithium disilicate veneer was used was significantly lower than when a zirconia veneer was used. Full article