Search Results (321)

This study investigated the tribological and mechanical properties of chromium nitride (CrN and CrN/DLC) coatings applied to 316L steel in an artificial blood environment. The wettability of the tested surfaces was determined and the hardness was also tested using the instrumental indentation. Friction-wear tests were performed using a TRB³ tribometer in a rotating ball-on-disc configuration. The tests were performed under dry friction conditions and with lubrication using artificial blood at pH 7.45 (neutral environment) and pH 7.15 (acidified environment). Wear of the friction pairs was examined using an interferometric-confocal microscope. Artificial blood was chosen to simulate human body fluids. The use of the CrN/DLC coating reduced the coefficient of friction by 83% for dry friction, by 62% for friction with neutral artificial blood lubrication, and by 69% for friction with acidic artificial blood lubrication, respectively. Despite the increased coefficient of friction of the CrN coating, its use also contributed to reduced material wear. Full article

Objective: This study aimed to investigate the effects of dual-task stroboscopic visual training (DTSVT) on balance, functional mobility, and gait in children who are hard-of-hearing. Methods: This randomized controlled study included 31 children (17 girls, 14 boys) with congenital sensorineural hearing loss. Participants were assigned to one of three groups: control group, conventional balance training (CBT) group, and DTSVT group. The CBT and DTSVT groups participated in an exercise program for 16 weeks, twice weekly, for 40 min (a total of 24 sessions). Static balance was assessed using the Tandem Romberg test and Single-Leg Stance (SLS) test, while dynamic balance was evaluated using the Functional Reach Test (FRT), balance disc test, and the Four Square Step Test (FSST). The Pediatric Balance Scale (PBS) was used as a subjective balance assessment. Functional mobility was assessed using the Timed Up and Go (TUG) Test, Step Test, 10 m Walk Test (10 MWT), and Functional Gait Assessment (FGA). Postural sway parameters were recorded using the GyKo device, including Sway Area (EA, cm²), Distance Length (DL, cm), Length (anterior–posterior (AP)) (cm), Length (medial–lateral (ML)) (cm), Mean Distance (D) (cm), Mean Distance (AP) (cm), and Mean Distance (ML) (cm). Results: Significant between-group differences were primarily observed in favor of the DTSVT group post-treatment, particularly in PBS scores, GyKoDL values during the eyes-open SLS test, and TUG test completion times (p < 0.05). Some baseline differences were noted among groups in functional reach distance, FSST completion time, and eyes-closed duration on the Balance Disc test (p < 0.05). Within-group comparisons revealed significant improvements in FSST times in both intervention groups, reduced postural sway parameters during the FRT in the DTSVT and control groups, and increased eyes-closed Tandem Romberg duration in the CBT group (p < 0.05). Most other outcome measures did not demonstrate statistically significant changes either within or between groups (p > 0.05). Conclusions: Dual-task stroboscopic visual training was more effective than conventional balance training in improving specific aspects of balance and functional mobility in children who are hard-of-hearing. These findings highlight the potential of adding cognitively demanding and visually engaging balance tasks to rehabilitation programs for this population. Larger and more diverse samples in future studies are needed to enhance the generalizability of these results. Studies that assess balance and gait using standardized clinical or laboratory tests may be particularly valuable. Given the small sample size and multiple comparisons, the results should be considered preliminary and exploratory. Full article

We are witnessing a global commitment to sustainable mobility that requires advanced materials and manufacturing techniques, such as fused filament fabrication (FFF), to create lightweight, durable, and recyclable machine components. Acknowledging that friction and wear significantly contribute to energy loss globally, developing high-performance polymeric materials with customizable properties is essential for greener mechanical systems. FFF inherently drives resource efficiency and offers the geometric freedom necessary to engineer complex internal structures, such as the gyroid pattern, enabling substantial mass reduction. This study evaluates the tribological performance of FFF-printed thermoplastic polyurethane (TPU 82A) specimens fabricated with three distinct gyroid infill densities (10%, 50%, and 100%). Ball-on-disc testing was conducted under dry sliding conditions against a 100Cr6 spherical ball, with a constant normal load of 5 N, resulting in an initial maximum theoretical Hertz contact pressure of 231 MPa, over a total sliding distance of 300 m. Shore A hardness and surface roughness (R_a) were also measured to correlate mechanical and structural characteristics with frictional response. Results reveal a non-monotonic relationship between infill density and friction, with a particular absence of quantifiable mass loss across all samples. The intermediate 50% infill (75.9 ± 1.80 Shore A) exhibited the peak mean friction coefficient of $\overline{\mu }=1.002$ (${\mu }_{\max }=1.057$), which can be attributed to its balanced structural stiffness that promotes localized surface indentation and an increased real contact area during sliding. By contrast, the rigid 100% infill (86.3 ± 1.92 Shore A) yielded the lowest mean friction ($\overline{\mu }$ = 0.465), while the highly compliant 10% infill (44.3 ± 1.94 Shore A) demonstrated viscoelastic energy damping, stabilizing at $\overline{\mu }$ = 0.504. This work highlights the novelty of using FFF gyroid architectures to precisely tune TPU 82A’s tribological behavior, offering design pathways for sustainable mobility. The ability to tailor components for low-friction operations (e.g., μ ≈ 0.465 for bushings) or high-grip requirements (e.g., μ ≈ 1.002 for anti-slip systems) provides eco-efficient solutions for automotive, railway, and micromobility applications, while the exceptional wear resistance supports extended service life and material circularity. Full article

This study presents a comprehensive review of the CLH index, a predictive tool developed to estimate the wear of tunnel boring machine (TBM) disc cutters operating in hard rock conditions. The CLH index provides a simplified, time-efficient, and cost-effective alternative to conventional wear prediction methods by employing a statistically derived empirical formula. The methodology is based on the identification and quantitative assessment of key rock properties that influence cutter wear. A detailed statistical analysis was conducted to validate the index, quantify potential errors, and determine confidence levels. As part of this review, updated reference tables are proposed to facilitate cutter wear estimation without the need for preliminary laboratory testing. These tables are derived from empirical data obtained at the Rock Mechanics Laboratory of the Higher Technical School of Mining and Energy Engineers (ETSIME-UPM), using operational records from TBM excavation in multiple Spanish high-speed railway tunnels, with a total length exceeding 120 km. The results confirm the reliability and practical applicability of the CLH index as a decision-support tool in TBM performance forecasting and maintenance planning. Full article

This study examines the effect of an AlTiN/TiSiXN two-layer coating on the tribological performance of HS6-5-2C steel under dry friction conditions. Tribological assessments were conducted using a tribometer and a calotester with a ball-on-disc configuration, involving HS6-5-2C steel discs (both uncoated and coated with AlTiN/TiSiXN) and 100Cr6 steel balls. Analyses, including surface topography, microstructure, and chemical composition, were performed utilising confocal microscopy, atomic force microscopy, and scanning electron microscopy with energy dispersive spectroscopy. The hardness and elastic modulus of the coating and substrate were determined through nanoindentation techniques. The coating exhibited a hardness of approximately 38 GPa and high elasticity, substantially enhancing the tribological characteristics of the system. Notably, the coated specimens exhibited friction coefficients approximately 10% lower than those of the uncoated steel, while wear on the coated discs was reduced by more than 90% in comparison to their uncoated counterparts. Wear rate evaluations of the counter-samples indicated a slightly increased wear of the balls—approximately 21%—when in contact with the coated discs, which can be attributed to the high hardness of the coating. These results substantiate the superior efficacy of the AlTiN/TiSiXN coating in improving wear resistance and reducing friction. Full article

As a functional coating, the wear-resistant Cr coating is of considerable importance in metal plating. In the present paper, S235 steel samples were electrodeposited with 5 µm thick Cr coating at current densities of 15, 27 and 40 A dm⁻². Nanoindentation was performed to measure the hardness of samples with electroplated Cr coating. Under the defined electroplating process conditions, the Cr coating hardness varied as a function of current density: the minimum average H_IT value of 11.4 GPa was measured at a current density of 15 A dm⁻² and the maximum average H_IT value of 12.9 GPa was measured at 40 A dm⁻². Tribological characteristics of coated samples were determined using the ball-on-disc tribo-method with surface evaluation of tribo-track on the confocal and electron microscope. The Cr coating deposited at 15 A dm⁻² had the lowest wear resistance with a wear rate of 12.76 × 10⁻¹⁵ m³ (Nm)⁻¹. The Cr coating deposited at 40 A dm⁻² had the highest wear resistance on the sample with a wear rate of 3.84 × 10⁻¹⁵ m³ (Nm)⁻¹. Full article

Hard Cr-Al-Si-B-(N) coatings were deposited in Ar and Ar–15%N₂ medium by d.c. magnetron sputtering of composite targets manufactured using self-propagating high-temperature synthesis. The structure of the coatings was studied by X-ray diffraction, scanning and transmission electron microscopy, energy dispersion spectroscopy, and glow discharge optical emission spectroscopy. The coating properties were determined by nanoindentation, scratch testing, and tribological pin-on-disc testing at room and elevated temperatures. The oxidation resistance and diffusion barrier properties of the coatings were also evaluated. The results obtained showed that non-reactive coatings had a coarse crystalline structure and contained Cr₅Si₃, CrB_x, and Cr₂Al phases. The introduction of nitrogen into the coating composition promoted crystallite refinement and structural amorphization. Non-reactive CrAl₄Si₁₁B₂₁ coatings had a maximum hardness up to 29 GPa and an elastic modulus up to 365 GPa. The introduction of nitrogen into the coating composition resulted in a 16–32% reduction in mechanical properties. The CrAl₆Si₁₂B₅N₂₅ coating, which exhibited maximal plasticity index H/E = 0.100 and resistance to plastic deformation H³/E² = 0.247 GPa, was characterized by a minimum wear rate Vw = 5.7 × 10⁻⁶ mm³N⁻¹m⁻¹ and a friction coefficient of 0.47. While the CrAl₁₈Si₁₁B₅N₂₆ coating demonstrated a record level of oxidation resistance and successfully resisted oxidation up to a temperature of 1300 °C. Full article

This article presents studies of surface layers produced by electro-spark deposition (ESD) on cast iron using a W-Ni-Co sintered electrode. To minimize the number of required experiments, a two-factor, five-level Hartley experimental design was chosen. The assessment involved observing the effect of voltage and capacitor capacity during the ESD process (on layer thickness and wear of the sample and counter-sample under technically dry friction conditions). Microscopic and tomographic observations were performed to analyze the thickness and structure of the layers. Image analysis methods were employed to examine the cross-section of the layers. ESD diffusion analyses were performed on the produced layer. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) were performed to characterize the microstructure and composition of the coating. In addition, in order to evaluate the performance properties of tungsten coatings, the tribological tests were also conducted on a TRB³ Ball-on-Disc testing device. Hardness tests confirm an increase in the hardness of cast iron with a tungsten layer by over 400 µHV. The tests showed that higher voltages during the ESD process result in thicker layers and reduced wear of the sample with a tungsten layer at the expense of increased wear of the counter-sample (ball). Full article

Aircraft engine turbine discs operate under extreme conditions that limit their service life. Laser cladding of AlCoCrFeNi HEA coatings presents a viable solution to enhance their durability. This study optimizes the laser cladding process parameters—specifically, laser power, scanning speed, and powder feed rate—using the Taguchi method in conjunction with grey relational analysis. The optimal parameter set (1450 W, 480 mm/min, 4 r/min) resulted in a coating with a width of 2.93 mm, a height of 1.20 mm, a dilution rate of 22.6%, and a hardness of 532 HV. The optimized process significantly improved hardness by approximately 15% while reducing dilution and elemental segregation in comparison to the initial parameters. This research illustrates the effectiveness of multi-objective optimization in enhancing coating performance, providing a practical approach for the surface strengthening of critical components, such as turbine discs in aircraft engines, under extreme conditions. Full article

The present contribution showcases the potential brake emission reduction with Cr₂O₃ (chromium oxide) and WC-CoCr (tungsten carbide–chromium–cobalt) rotor coatings, as realized in our joint public–private research consortium. Particulate matter (PM) emissions from automotive braking systems have been characterized using a pin-on-disc tribometer equipped with particle measurement devices: a CPC (Condensation Particle Counter), an APS (Aerodynamic Particle Sizer), an SMPS (Scanning Mobility Particle Sizer), and a PM_2.5 sampling unit. Brake pad samples made from the same low-steel friction material were tested against a grey flake cast iron disc and two types of custom coated discs: a Cr₂O₃-coated disc and a WC-CoCr-coated disc. The friction pairs were investigated at a constant contact pressure of 1.2 MPa while the sliding velocity varied during the test, starting with 25 sequences at 3.6 m/s, followed by 19 sequences at 6.1 m/s, and finishing with 6 sequences at 11.2 m/s. The test results show encouraging 64% to 84% reductions in particle number (PN) emissions between 4 nm and 3 µm and 84% to 95% reductions in mass emissions (PM_2.5) thanks to the respective coated discs. SEM-EDXS (Scanning Electron Microscopy and Energy Dispersive X-ray Spectroscopy) analyses show that the hardness and roughness of the discs, the chemical reactivity (oxidation), and the abrasiveness of the three friction pairs are parameters that might explain this reduction in emission. Full article

Surface roughness influences biofilm adhesion on denture base materials, impacting oral health. Despite advances in polymeric denture materials, the effects of common cleaning protocols on their surface texture remain inadequately characterized. This study investigated the influence of toothbrush abrasion on the surface texture of dimethyl methacrylate-based (DMA, printed: V-Print dentbase), polymethyl methacrylate (PMMA, milled: VITA Vionic Base, pressed: IvoBase Hybrid), polyamide (PA, pressed: Bre.flex), and polyether ether ketone (PEEK, milled: Juvora Disc). The specimens were fabricated as polished discs. The Vickers and Martens hardness, indentation modulus, elastic and plastic part of indentation work, and indentation creep were determined. Toothbrushing simulation and surface texture analysis were conducted in three steps: 1800, 1800, and 3600 cycles using water, dish detergent, or toothpaste slurry. The surface texture parameters Sa, Sal, Sdr, Sku, and Ssk were determined using confocal laser scanning microscopy and suitable filtering (S-F and S-L surface). Sa, Sal, and Sdr showed significant changes depending on the choice of medium and the material used. The duration had a small effect (three-way ANOVA; all p < 0.001). DMA showed minor surface changes. Milled and pressed PMMA exhibited similar surface deformities due to wide valleys that were not considered critical for biofilm adhesion. PA showed the lowest and PEEK the highest Vickers and Martens hardness. However, both PA and PEEK exhibited surface changes that could promote biofilm development. These findings suggest that denture cleaning recommendations should remain material-specific. Regular surface inspections and repolishing are necessary to reduce the risk of biofilm formation on PA or PEEK-containing dentures. Full article

Grey cast iron brake discs with lamellar graphite (GJL) offer excellent strength and thermal conductivity but are prone to wear and dust emissions. To mitigate these issues, a multilayer coating was applied via Laser Metal Deposition (LMD), comprising a 316L stainless steel base layer and a WC-reinforced top layer. This study examines the microstructural evolution of the coatings under simulated thermomechanical and corrosive conditions using a brake shock corrosion test. Microstructural characterization was performed via Scanning Electron Microscopy (SEM) and Electron Backscatter Diffraction (EBSD), focusing on grain size, orientation, and texture before and after testing. EBSD analysis revealed significant grain coarsening, with sizes increasing from below 20 µm to 30–60 µm, and a shift toward <101> texture. Hardness measurements showed a reduction in the WC-reinforced layer from 478 HV to 432 HV and in the 316L base layer from 232 HV to 223 HV, confirming the influence of thermomechanical stress. SEM analysis revealed a transition from horizontal cracks—caused by residual stress during LMD—to vertical microcracks propagating from the substrate, activated by braking-induced loads. These findings provide insights into the microstructural response of LMD coatings under realistic service conditions and underscore the importance of grain boundary control in designing durable brake disc systems. Full article

In view of the need to increase the durability of working tools exposed to intense friction, this study analysed hybrid coatings (TiAlCN, AlTiCN, AlCrTiN, TiN, CrN) with a DLC (Diamond-Like Carbon) layer, deposited using PVD (Physical Vapour Deposition) methods (arc evaporation and magnetron sputtering). The structural characteristics of the coatings were determined using SEM (Scanning Electron Microscope) and AFM (Atomic Force Microscope) microscopy, as well as Raman spectroscopy, which confirmed the compact structure and amorphous nature of the DLC layer. Tribological tests were performed using a ball-on-disc test, revealing that DLC hybrid coatings significantly reduce the coefficient of friction (stabilisation in the range of 0.10 to 0.14 due to DLC graphitisation), limiting tool wear even under increased load. The SEM-EDS (Scanning Electron Microscope-Energy Dispersive Spectroscopy) microscopic examination revealed that the dominant wear mechanisms are abrasive and adhesive damage, and the AlCrTiN/DLC system is characterised by low wear and high adhesion (L_c = 10⁵ N), making it the optimal configuration for the given loads. Microhardness tests showed that high hardness does not always automatically translate into increased wear resistance (e.g., the AlTiCN coating with 4220 HV showed the highest wear), while coating systems with moderate hardness (TiAlCN/DLC, CrN/DLC) achieved very low wear values (~0.17 × 10⁻⁵ mm³/Nm), which highlights the importance of synergy between the hardness of the sublayer and the low friction of DLC in the design of protective coatings. Full article

Objective: This study aimed to evaluate the color stability and microhardness of two resin composites, a BPA-based composite (Luna) and a BPA-free composite (Luna 2), after immersion in chlorhexidine (CHX), using two different polishing protocols. Methods: Disks (7 mm diameter × 2 mm thickness) were prepared and divided into three groups per material: unpolished, Sof-Lex, and FlexiDisc polished (n = 20 per group). The specimens were immersed daily in either 0.12% CHX or distilled water for 21 days. Color change (ΔE) was measured at 7, 14, and 21 days using a spectrophotometer. Microhardness was evaluated at each time point using a Vickers hardness tester (200 g load, 10 s dwell time). Results: Luna 2 exhibited significant discoloration from day 14, while Luna showed significant color change on day 21 (p < 0.05). After 21 days of CHX immersion, unpolished Luna reached a ΔE value of 6.27 ± 1.69, exceeding the clinically acceptable threshold. At 14 days, Sof-Lex polishing significantly improved color stability compared to unpolished controls for both materials (p < 0.05). No significant differences were observed between the two polishing systems over time (p > 0.05). Luna 2 demonstrated significantly higher microhardness at all evaluated time points (p < 0.001). Both composites exhibited slight reductions in microhardness over time, which were more pronounced in Luna (p < 0.001). Conclusions: Polishing enhanced the color stability of both composites. Luna 2 exhibited superior microhardness compared to Luna, and polishing had no significant effect on this property. Given the increasing clinical shift toward BPA-free materials due to biocompatibility concerns, these findings offer relevant guidance for optimizing the long-term esthetic and mechanical performance of modern resin-based restorations. Full article

Understanding the combined effects of edge width and cutter ring shape on the rock-breaking performance is critical for optimising disc cutter design. The intrusion test serves as an effective approach for investigating the rock-breaking mechanism of disc cutters. In this study, a two-dimensional discrete element method (DEM) model was established to simulate the intrusion process of a single disc cutter. Three commonly used disc cutter types were analysed: disc cutter with flat edge (FEDC), disc cutter with rounded edge (REDC) and disc cutter with alloy tooth (ATDC). The edge widths ranging from 10 mm to 24 mm were examined to assess their influence on rock crack propagation, stress distribution, cutting force and specific cutting energy. The FEDC and REDC exhibited face-contact extrusion breaking, whereas the ATDC was line-contact embedding breaking. The crack extension range, crack number, force chain intensity, stress distribution, rock-breaking force and specific cutting energy ranks are as follows: FEDC > REDC > ATDC. The ATDC generated a higher proportion of tensile cracks compared to the FEDC and REDC, though with fewer long cracks. The rock-breaking efficiency of the FEDC was lower, whereas the REDC and ATDC exhibited higher efficiency. With the increase in edge width, the force chain distribution became more concentrated, leading to greater internal rock damage, and the number and length of cracks increased significantly. Cracks initially expanded laterally at smaller edge widths but extended downward as edge width increased. The peak force and specific cutting energy increased with increasing edge width; the peak force at an edge width of 24 mm is approximately 3.5 times that of an edge width of 10 mm. The REDC is preferable in hard rock formations, and the ATDC is more effective in soft rock formations. The edge width should be determined based on rock properties and thrust capacity. Full article