Search Results (129)

In electric vehicle (EV) drivetrains, lubricant films must not only mitigate friction and wear but also manage stray currents to safely dissipate stray charge and avoid micro-arcing. This study directly compares how a conventional antiwear additive (ZDDP) and a long-chain, ashless, sulfur-free phosphite ester (Duraphos AP240L) manage this balance under current-carrying boundary lubrication conditions. Reciprocating steel-on-steel tests were conducted at fixed load and speed with applied current densities of 0, 0.02, and 42.4 A/cm². Friction and four-probe electrical contact resistance (ECR) were measured in situ, and impedance of tribofilms was measured over a 1–10⁵ Hz range after friction test. In the presence of ZDDP, ECR initially increased and then decreased to a value that was as low as the initial direct contact of two solid surfaces or even lower sometimes. During the initial stage with high ECR, a well-defined impedance semicircle was observed in the Nyquist plot; after forming the tribofilm with low ECR, frequency dependence of impedance could not be measured due to the very low resistance. The decrease in ECR suggested a structural evolution of the anti-wear film on the substrate. However, post-test wear analysis indicated that the formation of this film was accompanied by tribochemical polishing of the countersurface and sometimes pitting of the substrate, which may have been due to localized electrical discharge producing trenches deeper than ~0.5 µm; in additive-free base oil, wear was dominated by ploughing with micro-cutting of the substrate. In contrast, AP240L performed better in terms of friction and wear, showing a remarkable ~30% lower coefficient of friction, while the overall cycle dependence of ECR was similar to the ZDDP case. AP240L showed negligible boundary film controlled wear producing a shallow, smooth track (depth < 0.2 µm) during the friction test, and there was no sign of electrical arc damage. These findings support long-chain, ashless, sulfur-free phosphite esters as promising candidates for EV boundary lubrication where both mechanical and electrical protection are required. 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

The accurate modelling of material removal mechanisms in grinding processes requires precise constitutive equations describing dynamic material behaviour under extreme strain rates and large deformations. This study presents a novel methodology for optimising the Johnson–Cook (J–C) constitutive model parameters for micro-grinding applications, addressing the limitations of conventional mechanical testing at strain rates exceeding 10⁵ s⁻¹. The research employed single abrasive grain micro-cutting experiments using a diamond Vickers indenter on aluminium alloy 7075-T6 specimens. High-resolution topographic measurements (130 nm lateral resolution) were used to analyse the scratch geometry and lateral material displacement patterns. Ten modified J–C model variants (A1–A10) were systematically evaluated through finite element simulations, focusing on parameters governing plastic strengthening (B, n) and strain rate sensitivity (C). Quantitative non-conformity criteria assessed agreement between experimental and simulated results for cross-sectional areas and geometric shapes of material pile-ups and grooves. These criteria enable an objective evaluation by comparing the pile-up height (h), width (l), and horizontal distance to the peak (d). The results demonstrate that conventional J–C parameters from Hopkinson bar testing exhibit significant discrepancies in grinding conditions, with unrealistic stress values (17,000 MPa). The optimised model A3 (A = 473 MPa, B = 80 MPa, n = 0.5, C = 0.001) achieved superior convergence, reducing the non-conformity criteria to Σk_A = 0.46 and Σk_K = 1.16, compared to 0.88 and 1.67 for the baseline model. Strain mapping revealed deformation values from ε = 0.8 to ε = 11 in lateral pile-up regions, confirming the necessity of constitutive models describing material behaviour across wide strain ranges. The methodology successfully identified optimal parameter combinations, with convergence errors of 1–14% and 7–60% on the left and right scratch sides, respectively. The approach provides a cost-effective alternative to expensive dynamic testing methods, with applicability extending to other ductile materials in precision manufacturing. Full article

Blackberry (Rubus L.) cultivation in Kazakhstan is constrained by the limited availability of certified planting material and the absence of standardized micropropagation protocols adapted to local conditions. This study aimed to optimize the key stages of in vitro culture for the cultivars ‘Natchez’, ‘Black Magic’, ‘Osage’, and ‘Heaven Can Wait’, including explant sterilization, culture initiation, shoot multiplication, and acclimatization. A sequential sterilization scheme using 70% ethanol followed by 1% sodium hypochlorite ensured high explant survival. Shoot initiation was most efficient on MS medium supplemented with 0.1 mg/L BAP, whereas multiplication was enhanced by 0.5 mg/L BAP and 0.1 mg/L GA₃. In the subsequent rooting stage, microcuttings formed stable root systems under ex vitro conditions in agroboxes, confirming that the optimized protocol ensured not only high survival during initiation but also a successful transition to the rooting phase, which is essential for further acclimatization. During ex vitro acclimatization, the application of humic acid, nanosilicon, or succinic acid improved survival under agrobox microventilation. The developed approach provides a reliable framework for producing healthy, adapted plants of the evaluated cultivars and contributes to establishing domestic propagation systems for reducing reliance on imported planting material. Full article

Vegetative propagation through stem cuttings and in vitro microcuttings enables large-scale multiplication of superior genotypes in various crop species. This approach is widely used both to propagate and select trees with desirable genetic traits as well as to preserve a significant proportion of genetic diversity. However, successful plant regeneration using this technique requires the development of an adventitious root (AR) system at the base of cuttings or microcuttings. Reduced root formation and functionality strongly limit the application of vegetative propagation, both in vivo and in vitro. The complex process of AR development is greatly influenced by the physiological state of the donor plant, as well as by genetic and environmental factors. Among the environmental factors involved, light quality and intensity have been mainly studied empirically. This review summarizes advances in understanding how light quantity and quality influence in vitro rooting of micropropagated plants, emphasizing species-specific responses. Furthermore, medium components such as sugars and growth regulators, which interact significantly with light, are also considered. Based on existing studies across different plant species, particularly in the absence of growth regulators, the most effective spectrum for root induction is a temporary enrichment of red light, either alone or combined with small amounts of blue or green light. An efficient root growth occurs when the explants are re-exposed to white light, typically at intensities of 40–50 μmol m⁻² s⁻¹. After root development, exposing the microcuttings to higher intensities could help acclimatization. Finally, considering its capacity to precisely regulate light quality and intensity, LED technology offers a valuable tool for optimizing the rooting process and reducing production costs. Full article

Composite materials are widely utilized for their excellent properties; however, the mismatch in phase response during processing often induces surface and subsurface damage. While reducing the cutting depth is a common strategy to improve quality, it shifts the material removal mechanism from shear to ploughing–extrusion, which can, in fact, degrade the final surface integrity. Energy field assistance is a promising approach to suppress this issue, yet its underlying mechanism remains insufficiently understood. This study investigates high-silicon aluminum alloy by combining turning experiments with molecular dynamics simulations to elucidate the origin and evolution of damage under different energy fields, establishing a correlation between microscopic processes and observable defects. In conventional turning, damage propagation is driven by particle accumulation and dislocation interlocking. Ultrasonic vibration softens the material and confines plastic deformation to the near-surface region, although excessively high transient peaks can lead to process instability. Laser remelting turning disperses stress within the remelted layer, significantly inhibiting defect expansion, but its effectiveness is highly sensitive to variations in cutting depth. The hybrid approach, laser remelting ultrasonic vibration turning, leverages the dispersion buffering effect of the remelted layer and the localized plastic deformation from ultrasonication to reduce peak loads, control deformation depth, and suppress defects, while simultaneously mitigating the depth sensitivity of damage and maintaining removal efficiency. This work clarifies the mechanism by which a composite energy field controls damage in the micro-cutting of high-silicon aluminum alloy, providing practical guidance for the high-quality machining of composite materials. Full article

Erosion wear is a major cause of surface degradation in metallic materials exposed to harsh marine environments. In this study, the erosion wear resistance of the 18Ni300 maraging steel repaired by underwater direct metal deposition (UDMD) is investigated. Results show that UDMD is successfully applied to repair the 18Ni300 samples in underwater environment. Full groove filling and sound metallurgical bonding without cracks are achieved, demonstrating its potential for underwater structural repair. Microstructural analyses reveal good forming quality with fine cellular structures and dense lath martensite in the deposited layer, attributed to rapid solidification under water cooling. Compared to in-air DMD, the UDMD sample exhibits higher surface microhardness due to increased dislocation density and microstructural refinement. Erosion wear behavior is evaluated at 30° and 90° impingement angles, showing that wear mechanisms shift from micro-cutting and plowing at 30° to indentation, crack propagation, and spallation at 90°. The UDMD samples demonstrate superior erosion wear resistance with lower mass loss, particularly at 30°, benefiting from surface work hardening and microstructural advantages. Progressive surface hardening occurs during erosion due to severe plastic deformation, reducing wear rates over time. The combination of refined microstructure, high dislocation density, and enhanced work hardening capability makes UDMD-repaired steel highly resistant to erosive degradation. These findings confirm that UDMD is a promising technique for repairing marine steel structures, offering enhanced durability and long-term performance in harsh offshore environments. Full article

Self-fluxing Ni-based coatings (NiCrFeBSiC) were deposited through gas-flame spraying and evaluated in three conditions: as-sprayed, flame-remelted, and furnace-heat-treated (1025 °C/5 min). Phase analysis (XRD) revealed FeNi₃ together with strengthening carbides/borides (e.g., Cr₇C₃, Fe₂₃(C,B)₆); post-treatments increased lattice order. Cross-sectional image analysis showed progressive densification (thickness ~805 → 625 → 597 µm) and a drop in porosity from 7.866% to 3.024% to 1.767%. Surface roughness decreased from Ra = 31.860 to 14.915 to 13.388 µm. Near-surface microhardness rose from 528.7 ± 2.3 to 771.6 ± 4.6 to 922.4 ± 5.7 HV, while adhesion strength (ASTM C633) improved from 18 to 27 to 34 MPa. Wettability followed the densification trend, with the contact angle increasing from 53.152° to 79.875° to 89.603°. Under dry ball-on-disk sliding against 100Cr6, the friction coefficient decreased and stabilized (0.648 ± 0.070 → 0.173 ± 0.050 → 0.138 ± 0.003), and the counterbody wear-scar area shrank by ~95.6% (0.889 → 0.479 → 0.0395 mm²). Wear-track morphology evolved from abrasive micro-cutting (as-sprayed) to reduced ploughing (flame-remelted) and a polishing-like regime with a thin tribo-film (furnace). Potentiodynamic tests indicated the lowest corrosion rate after furnace treatment (CR ≈ 0.005678 mm·year⁻¹). Overall, furnace heat treatment provided the best structure–property balance (lowest porosity and Ra, highest HV and adhesion, lowest and most stable μ, and superior corrosion resistance) and is recommended to extend the service life of NiCrFeBSiC coatings under dry sliding. Full article

CoCrFeNiMn HEA-based composites with Cr₃C₂, 15% Ag, and different mass fractions of CaF₂/BaF₂ eutectic fluoride were fabricated by spark plasma sintering. The tribological properties and wear mechanism of the composites were investigated from RT to 800 °C. The friction coefficients of CoCrFeNiMn-Cr₃C₂-Ag-CaF₂/BaF₂ composites decrease from RT to 800 °C except for 400 °C. At 800 °C, with the increasing mass fraction of the eutectic fluoride, the friction coefficient of the composite decreases from 0.53 to 0.25. The wear rates of the composite with 15% CaF₂/BaF₂ eutectic fluoride decrease significantly at high temperatures. The CoCrFeNiMn-Cr₃C₂-Ag-15%CaF₂/BaF₂ composite exhibits the lowest wear rates at 400 °C, 600 °C, and 800 °C, which are 4.47 × 10⁻⁶ mm³/N·m, 5.15 × 10⁻⁶ mm³/N·m, and 2.42 × 10⁻⁶ mm³/N·m, respectively. At low temperatures, the tribological mechanisms of the composites are micro-plowing and micro-cutting, and Ag is formed as a lubricating film to reduce the friction coefficient. At high temperature, fluorides form a transfer film on the wear scar surface, providing a lubricating effect. Also, the oxide layers and chromate are formed on the worn surfaces of the composites, which are beneficial for improving the wear resistance. Based on the mechanical properties and tribological behavior, the CoCrFeNiMn-Cr₃C₂-Ag-15%CaF₂/BaF₂ composite demonstrates the best comprehensive properties. Full article

As a key component of aero transmission systems, internal splines suffer from problems of low efficiency and poor precision in traditional lapping processes due to geometric deformation and high hardness after heat treatment. To address this, this study proposes an ultrasonic vibration lapping technology, which combines the synergistic mechanism of high-frequency vibration and free abrasive particles to achieve efficient and precise machining of small-sized hardened internal splines. By establishing an abrasive grain impact trajectory model and a rolling abrasive grain material removal model, the mechanisms of micro-cutting and impact removal of abrasive particles under ultrasonic vibration are revealed. Based on the local resonance theory, a longitudinal ultrasonic vibration system is designed, and its resonant frequency is optimized through finite element modal analysis. An ultrasonic lapping experimental platform is built, and heat-treated 9310 internal spline samples are used for experimental verification. The results show that, compared with traditional manual lapping, ultrasonic vibration lapping significantly improves the tooth profile and tooth lead deviations. After measurement, following ultrasonic vibration lapping, both the total tooth profile deviation and tooth lead deviation of the internal spline meet the Grade 6 accuracy requirements specified in GB/T 3478.1-2008 Cylindrical straight-tooth involute splines (Metric Module, Tooth Side Fit)—Part 1: General. This study confirms that ultrasonic vibration lapping can effectively correct the geometric accuracy of tooth surfaces and suppress thermal damage, and provides an innovative solution for the high-quality repair of aero transmission components. Full article

This study investigates the tribological behavior and wear mechanisms of Q235 steel components subjected to abrasive interaction with rice, a critical challenge in agricultural machinery performance and longevity. We employed a comprehensive multi-scale framework, integrating bench-top tribological testing, advanced Discrete Element Method (DEM) coupled with a wear model (DEM-Wear), and detailed surface characterization. Bench tests revealed a composite wear mechanism for the rice–steel tribo-pair, transitioning from mechanical polishing under mild conditions to significant soft abrasive micro-cutting driven by the silica particles inherent in rice during high-load, high-velocity interactions. This elucidated fundamental friction and wear phenomena at the micro-level. A novel, calibrated DEM-Wear model was developed and validated, accurately predicting macroscopic wear “hot spots” on full-scale combine harvester header platforms with excellent geometric similarity to real-world wear profiles. This provides a robust predictive tool for component lifespan and performance optimization. Furthermore, fractal analysis was successfully applied to quantitatively characterize worn surfaces, establishing fractal dimension (Ds) as a sensitive metric for wear severity, increasing from ~2.17 on unworn surfaces to ~2.3156 in severely worn regions, directly correlating with the dominant wear mechanisms. This study offers a valuable computational approach for understanding and mitigating wear in tribosystems involving complex particulate matter, contributing to improved machinery reliability and reduced operational costs. Full article

In this study, solid particle erosion tests were conducted to evaluate the resistance of AISI 4340 (EN24) and 8620 alloy steels against silicon carbide (SiC). These steels were selected due to their high hardness, yield strength (σ_y), ultimate tensile strength (σ_uts) and elongation (%), which are significant parameters, influencing wear resistance. An erosion rig based on the ASTM G76-95 standard was used to perform the testing. Tests were carried out using different impact angles, 30°, 45°, 60° and 90°, with a particle velocity of 24 ± 2 m/s. The abrasive flow rate was 0.7 ± 0.5 g/min and the temperature was between 35 °C and 40 °C. Characterization techniques such as SEM were employed to identify the chemical composition of AISI 4340 and AISI 8620 steels and optical microscopy to determine the morphology of SiC abrasive particles. In addition, the SiC particle size was between 350 and 450 µm; it was determined by the particle size distribution technique. SEM micrographs were obtained to classify the wear mechanisms, characterized by micro-cutting, micro-ploughing, grooves, pitting actions and embedded particles on the surface at 30° and 90°. The results showed that AISI 8620 steel exhibited higher erosion resistance than AISI 4340 steel. Finally, AFM was used to evaluate the roughness variations before and after erosion tests, specifically in the central zone of the wear scars at 30° and 90° for both materials. Full article

AlCoCrFeNi coatings were electrospark-deposited (ESD) on H13 steel substrates, and their nano-mechanical and tribological properties under a load of 2 N, 4 N, 6 N, 8 N, and 10 N were investigated by utilizing a nanoindentation instrument and a reciprocating friction and wear tester, respectively. The morphologies, composition, and phase structure of the as-deposited and worn AlCoCrFeNi coating were characterized using SEM (Scanning electron Microscope), EDS (Energy dispersive spectrometer), and XRD (X-Ray Diffraction). The results showed that the as-deposited AlCoCrFeNi coating with a nanocrystalline microstructure mainly consists of a BCC and B2 phase structure, and a gradient transition of elements between the coating and the substrate ensures an excellent bond between the coating and the substrate. The hardness of the AlCoCrFeNi coating exhibits an 8% increase, while its elastic modulus is reduced by 16% compared to the H13 steel. The AlCoCrFeNi coating remarkably increased the tribological property of the H13 steel under various loads, and its wear mechanism belongs to micro-cutting abrasive wear whilst that of the H13 steel can be characterized as severe adhesive wear. The friction coefficient and weight loss of the AlCoCrFeNi coating decrease with increasing load, both following a linear relationship with respect to the applied load. As the load intensifies, the work hardening sensitivity and oxidation degree on the worn surface of the coating are significantly enhanced, which collectively contributes to the improved tribological performance of the AlCoCrFeNi coating. Full article

Synthetic seed technology is an innovative in vitro technique that provides improved storage capabilities for vegetative propagules. Its success mostly depends on the encapsulation matrix’s composition and the encapsulation procedure. The present study focuses on optimizing an encapsulation protocol for short-term storage and germplasm exchange using micro-cuttings of Salix tetrasperma. Among the different synthetic seed types evaluated, double-layered synthetic seeds (DLSs) exhibited the highest re-growth (93.6%) on MS medium supplemented with meta-Topolin (mT) (5.0 µM) and α-naphthalene acetic acid (NAA) (0.5 µM) after 8 weeks of culture. Viability assessment of non-embryogenic synthetic seeds during low-temperature storage (4 °C) demonstrated the enhanced resilience of double-layered synthetic seeds (DLSs) compared to their single-layered (SLS) counterparts. Following acclimatization in Soilrite^®-filled cups, 82% of the plantlets were successfully established in a greenhouse after four weeks. The increased activity and concentration of antioxidants in DLS-derived plantlets suggest the potential role of the extra layer of alginate in mitigating the effects of low-temperature stress during storage. SCoT molecular analysis confirmed the genetic integrity of the synthetic seed-derived plants. Full article

Ballota acetabulosa (L.) Benth. (syn. Pseudodictamnus acetabulosus (L.) Salmaki and Siadati), f. Lamiaceae, the Greek horehound, is a compact evergreen small shrub native to Greece, with hairy grey-green leaves, that bears small pink-purple flowers with green conical calyxes along its erect stems in late spring. The species stands out for its high resistance in xerothermic conditions and therefore it is advisable to promote its use in xeriscaping. The aim of this study was to develop an efficient protocol for in vitro propagation of B. acetabulosa for introduction into the horticultural and pharmaceutical industries. Shoot tip and single node explants derived from in vitro seedlings were cultured on MS medium with various cytokinin types and concentrations. Explants responded at almost 100% to produce high number of shoots on a medium with 1.0 mg L⁻¹ zeatin or 6-benzyladenine. However, there was intense hyperhydricity in the cultures, which was addressed in further experiments by increasing agar concentration from 8 to 12 g L⁻¹, preserving high multiplication indices (92% response, 10.2 shoots per explant). Microcuttings with 2–3 visible nodes, either from the apical part, including the apical meristem, or from the basal part of microshoots, as well as microshoot clusters, rooted 100% on full- or half-strength MS medium, respectively, regardless of the addition of indole-3-butyric acid (ΙΒA, 0.5–4.0 mg L⁻¹) in the rooting medium. However, middle level concentrations of IBA increased the number and length of roots produced, while the higher its concentration, the more and longer axillary shoots developed in the microcuttings during the rooting period. The acclimatization of all plantlets was completely successful (100%) in ex vitro conditions on peat/perlite substrate (1:1, v/v). Thus, efficient methods of producing propagation material to promote Ballota acetabulosa as a horticultural and medicinal plant were developed. In particular, rooting of microshoot clusters or microcuttings without the shoot tip, in the presence of 1.0 mg L⁻¹ IBA, leads to a plant of suitable shape for the floricultural market, without the need for further manipulation (pruning) in the nursery. Full article