Search Results (476)

Amorphous carbon is recognized as an excellent lubricating material; however, its tribological properties are significantly influenced by humidity. To elucidate the mechanism underlying this humidity dependence and to propose a novel enhancement method, we investigated and compared the tribological properties of hydrogenated amorphous carbon (a-C:H) and amorphous carbon/gold (a-C/Au) composite films. First, the friction coefficient of these carbon films under different humidity conditions was tested using a rotational ball-on-disk tribometer. Subsequently, we analyzed the morphology and structure of the sliding interface employing optical microscopy (OM), Raman spectroscopy, transmission electron microscopy (TEM), and high-resolution transmission electron microscopy (HRTEM). Finally, first-principle calculations were carried out to calculate the adsorption energy of water molecules on different surfaces. The results indicate that the friction coefficient of a-C:H film and the area of transfer film increase with the increase of humidity. This phenomenon can be attributed to the fact that water molecules enhance the interaction between the a-C:H film and steel counterfaces. Notably, in contrast, the friction coefficient of a-C/Au film demonstrates low sensitivity to humidity due to the formation of an Au transfer film that exhibits weak interaction with water molecules. These findings provide a promising strategy for developing environment-adaptive amorphous carbon films and play an important role in promoting the development of intelligent lubricating film. Full article

Improving the surface performance and service life of 60Si2Mn steel is an important issue in agricultural machinery. A FeCrV15 coating layer may exhibit excellent performance in wear resistance. This research focuses on studying the microstructure and wear resistance of the FeCrV15 coating layer at various scanning speeds through laser cladding. Microstructure, phase distribution, surface hardness, and wear resistance of the coating layers are analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), a microhardness tester, and laser confocal microscopy. The results indicate that the FeCrV15 alloy coating consists of γ-Fe, V₈C₇, and Cr₇C₃. The microhardness of the FeCrV15 coatings increases with the increase in the scanning speed. At a scanning speed of 8 mm/s, the highest microhardness reaches 727.5 ± 27 HV, approximately 2.5 times higher than the substrate. The friction and wear test of the coating is conducted using a 4 mm diameter Si₃N₄ ball grinding pair. The coatings prepared at different scanning speeds exhibit lower average coefficients of friction and wear rates compared to the substrate. Both the average coefficient of friction and wear rate decrease with increasing scanning speed. At a scanning speed of 8 mm/s, the lowest average coefficient of friction and the lowest wear rate were observed. The main wear mechanisms of the coating are oxidative wear and adhesive wear, with a small amount of abrasive wear. Full article

In this study, we analyze the extent to which thin hard coatings can serve as tribological protective layers for the selected plastic substrate materials PA12 (polyamide 12) und PEEK (polyetheretherketone), with and without fiber reinforcement. The approximately 1 µm thick coating variants ta-C, ta-C:N, and ta-C:B, which were applied using the laser arc process, are investigated. In oscillating sliding wear tests against a steel ball in an air atmosphere without lubricant, the wear of the coating and counter body is compared to analogous coating variants applied in parallel to AISI 52100 steel. The ta-C-based coatings show good adhesion strength and basic suitability as wear protection layers on the plastic substrates in the tribological tests. However, there are variations depending on the coating type and substrate material. The use of a Cr interlayer and its thickness also plays an important role. It is demonstrated that by coating under conditions where the uncoated plastic substrate would normally fail, a similarly good performance as with analogously coated steel substrates can be achieved by ta-C:N. Full article

Estrogens, widely used for therapeutic or contraceptive purposes, act as endocrine disruptors in aquatic systems and have adverse effects on a wide range of living organisms. Wastewater insufficiently treated by conventional methods is the main way for estrogens to enter aquatic systems. Therefore, the purpose of this paper is to develop a novel photocatalytic system for the removal of the estrogenic mixture estradiol valerate/norgestrel from wastewater. The photocatalytic modules are operated in a plug flow reactor system under a UV-A radiation field, and the photocatalyst (TiO₂, ZnO or TiO₂/ZnO) is immobilized on an inert support of glass balls that are strung on stainless-steel wire and arranged in rows along the photocatalytic modules. The photocatalysts were synthesized by the sol–gel method and then deposited on the inert glass support by the hot method, after which it was calcined for two hours at a temperature of 500 °C. The experimental results showed that the efficiency of photocatalytic degradation largely depends on the dose of photocatalyst. The dose of photocatalyst can be adjusted by adding or removing photocatalytic modules, each of which have an approximately equal amount of photocatalyst. The best result was obtained for the TiO₂/ZnO photocatalyst, the organic substrate being practically mineralized in 120 min, for which only two photocatalytic modules are needed. Full article

Wear is a major issue in industry, particularly with metal components. Therefore, it is crucial to investigate methods that offer increased resistance to this phenomenon. In this research, three coating systems (pure WC-CoCr and WC-CoCr/NiCrFeSiBC+Mo, 88:12 and 83:17 wt.%) were thermally sprayed on an AISI 1018 steel substrate through the High-Velocity Oxygen Fuel (HVOF) process. The coatings were characterized using a field emission scanning electron microscope (FESEM) equipped with the energy dispersive spectroscope (EDS) and X-ray diffractometry (XRD). An analysis of the wear rate for ball-on-flat linear reciprocating sliding tribological tests for the coatings was also carried out. The coating microstructure presents well-dispersed NiCrFeSiBC splats. The WC-CoCr/NiCrFeSiBC+Mo, 88:12, system has the highest wear resistance, decreasing by 30.2% at high loads compared to commercial WC-CoCr CERMETs, and also exhibits the highest fracture toughness. Analysis of wear tracks shows that the material removal at all charges occurred mainly by an abrasive wear mechanism. Full article

In this study, MoS₂ nanosheets have been prepared and treated ultrasonically with silver ammonia solutions. The MoS₂/Ag precursor was reduced using dopamine (DA) as reducing and linking agent at room temperature, and it was subjected to a hydrothermal treatment to produce MoS₂/Ag nanocomposites (denoted as MoAg). The MoAg samples were functionalized with N-oleoylethanolamine to improve dispersion in the base oil component of additives. Use of the functionalized MoAg (denoted as Fc-MoAg) as a lubricant additive for steel balls resulted in effective friction reduction and anti-wear. This work avoids ion exchange during exfoliation, and the Ag⁺ has been reduced to nano-silver particles by dopamine to enlarge the layer spaces of MoS₂. Taking the case of lubrication with base oil containing Fc-Mo_0.6Ag₁₅, the wear scar diameters and coefficients of friction of the steel balls were 0.428 and 0.098 mm, respectively, which were about three-fifths base oil. In addition, MoS₂/Cu and MoS₂/Ni nanocomposites were synthesized and the tribological properties associated with steel/steel balls assessed. The results demonstrate that all MoS₂/metal composites exhibit enhanced tribological behavior in the steel/steel pair tests. Both nanocomposite synergy and the tribofilm containing sulfide, oxide, carbide, and other compounds play important roles in achieving reduced friction and improved anti-wear. The friction and wear properties of base oil containing Fc-MoAg and commercial additives were evaluated using a four-ball wear tester with steel/steel, steel/zirconia and zirconia/zirconia pairs. The base oil containing Fc-MoAg delivered smaller coefficients of friction (COFs) and/or scarring groove depths than those observed with the use of pure base oil and base oil containing commercial additives. Full article

In this study, shot peening (SP), quenching and tempering (QT) heat treatment, baking heat treatment and Cr-plating technologies were used to enhance the hardness, tribological properties and corrosion resistance of AISI 4340M steel. The purpose of this study is to develop repair process technology for an overhaul of landing gear applied to the MRO process and establish a quality assurance system. The effects of SP, QT heat treatment, Cr-plating, stripping after Cr-plating and Cr-plating after stripping and re-SP on the tribological properties and corrosion resistance of AISI 4340M steel were investigated, and the obtained results were compared with the base AISI 4340M steel. One of the reasons for stripping after Cr-plating is to find out how many times stripping can be done after Cr-plating. Moreover, it is important to investigate the effect of re-SP after Cr-plating on the tribological properties and corrosion resistance. The tribological properties of the specimens were investigated using a ball-on-disk tribometer at room temperature against AISI 52100 steel for 60 min under dry conditions. The corrosion resistance was investigated using a potentiodynamic polarization test in NaCl 3.5% solution. The results showed that the application of SP, QT heat treatment, Cr-plating, stripping after Cr-plating and Cr-plating after stripping and re-SP had a significant effect on the tribological properties and corrosion resistance of AISI 4340M steel. The effects of SP and Cr-plating post-treatment technologies on the wear and corrosion enhancement and mechanisms were discussed based on the microstructural and surface morphology of worn and corroded surfaces. Full article

Due to the harsh operating conditions experienced by 1Cr17Ni2 steel, efforts were made to optimize its performance by subjecting 1Cr17Ni2 stainless steel to nitriding treatments at temperatures of 460 °C, 500 °C, and 550 °C, each for durations of 8 and 16 h. The formation state of its cross section was observed through a metallurgical microscope and scanning electron microscope, and it was characterized by hardness measurement. Through a ball-on-disk wear experiment, the adhesive wear and friction coefficient of its non-lubricated sliding were measured. The phase composition of its surface was measured by XRD. The results revealed that nitriding led to the formation of a modified layer on the surface of the samples, with a depth of 130 μm after nitriding at 550 °C for 16 h. The hardness of the modified layer exceeded that of the matrix, reaching up to 1400 Hv_0.1. X-ray diffraction (XRD) analysis of the sample surfaces indicated the presence of high-hardness phases such as CrN, γ′-Fe₄N, and ε-Fe_2-3N. This article predicts the mechanical properties of nitrided phases in high-alloy martensitic stainless steel through first-principles computational methods. We provide a reference for improving the performance of high-alloy steel after nitriding through a combination of theoretical calculations and experiments. Full article

Laboratory acoustic emissions (AEs) serve as small-scale analogues to earthquakes, offering fundamental insights into seismic processes. To ensure accurate physical interpretations of AEs, rigorous calibration of the acoustic system is essential. In this paper, we present an empirical calibration technique that quantifies sensor response, instrumentation effects, and path characteristics into a single entity termed instrument apparatus response. Using a controlled seismic source with different steel balls, we retrieve the instrument apparatus response in the frequency domain under typical experimental conditions for various piezoelectric sensors (PZTs) arranged to simulate a three-component seismic station. Removing these responses from the raw AE spectra allows us to obtain calibrated AE source spectra, which are then effectively used to constrain the seismic AE source parameters. We apply this calibration method to acoustic emissions (AEs) generated during unstable stick-slip behavior of a quartz gouge in double direct shear experiments. The calibrated AEs range in magnitude from −7.1 to −6.4 and exhibit stress drops between 0.075 MPa and 4.29 MPa, consistent with earthquake scaling relation. This result highlights the strong similarities between AEs generated from frictional gouge experiments and natural earthquakes. Through this acoustic emission calibration, we gain physical insights into the seismic sources of laboratory AEs, enhancing our understanding of seismic rupture processes in fault gouge experiments. Full article

Molybdenum disulfide coatings, particularly Microseal 200-1, have been extensively used as dry film lubricants for actuating mechanisms in space applications. Although Microseal 200-1 has historically been a popular choice for space missions, recent assessments indicate a need for reexamination. This study evaluates sliding friction in air and dry gaseous nitrogen atmospheres at ambient temperatures with both linear reciprocating and rotary unidirectional tribo-tests. Measurements are performed for Microseal 200-1 applied on substrates and surface treatments commonly used in aerospace components, particularly stainless steel and a titanium alloy. Our findings indicate that the friction of stainless steel balls sliding on Microseal 200-1-coated disks is significantly influenced by the environment as well as the disk substrate material. The average friction coefficient ranges from 0.12 to 0.48 in air and from 0.04 to 0.41 in dry gaseous nitrogen, and the amount of friction is consistently much higher for the Microseal 200-1 on the stainless steel than on the titanium alloy. Microscopy and surface analyses, including scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray fluorescence, of the coatings on stainless steel substrates reveals that the coatings are sparse and relatively thin, likely a key factor contributing to their high friction. This insight underscores the substrate dependence of this widely used coating and highlights the importance of detailed tribological testing in accurately assessing the tribological performance of commercial dry film lubricants, a key step towards improving the reliability and effectiveness of actuating mechanisms for space applications. Full article

This study explores the effect of steel ball size and proportion on mineral grinding characteristics using Discrete Element Method (DEM) simulations. Based on batch grinding kinetics, this paper analyzes the contact behavior during grinding, discussing particle breakage conditions and critical breakage energy. The results indicate that while increasing the size of the steel balls leads to higher collision energy, the collision probability decreases significantly; the opposite is true for smaller steel balls. Simulation results with different ball size combinations show that increasing the proportion of smaller balls does not significantly change the collision energy but greatly increases the collision probability, providing a basis for optimizing ball size distribution to improve grinding performance. Furthermore, appropriately increasing the proportion of smaller balls can reduce fluctuations in grinding energy consumption, thereby enhancing collision energy and collision probability while reducing energy costs. Liner wear results demonstrate that larger ball sizes increase liner wear, but different ball size combinations can effectively distribute the forces on the liner, reducing wear. Full article

Transferring the intraoral situation accurately to the dental laboratory is crucial for fabricating precise restorations. This study aimed to compare the dimensional accuracy of a new hydrophilic quadrofunctional vinyl polysiloxane (VPS) and polyether (PE), in combination with different impression techniques (mono-phase single step or dual-phase single step). The reference model simulated a partially edentulous mandible. Stainless-steel precision balls were welded to specific teeth and were used to detect dimensional deviations. Fifteen impressions were made for each of the following four test groups: (1) VPS mono-phase, (2) PE mono-phase, (3) VPS dual-phase, and (4) PE dual-phase. Global accuracy was measured by deviations from the reference model, while local accuracy focused on the trueness and precision of abutment tooth surfaces. Statistical analysis was conducted using ANOVA (α = 0.05). All distances were underestimated, with the highest global inaccuracies for the cross-arch distance, ranging from −82 µm to −109 µm. The abutment tooth surfaces showed excellent local accuracy for all the materials and techniques, with crown surface trueness < 10 µm and precision < 12 µm. Inlay surfaces had higher inaccuracies (trueness < 15 µm, precision < 26 µm). Within the limitations of this study, all impression materials and techniques can be used to produce models with clinically acceptable accuracy. Full article

Electrolytic plasma nitriding is an attractive chemical heat treatment used to improve the surface properties of steel by implementing nitrogen saturation. This method is widely applied to steel and iron-based alloys operating under various operating conditions. In this work, using liquid-phase plasma nitriding technology, a nitrided layer was obtained on the surface of 40CrNi steel in electrolytes of different concentrations. The microstructure and phase composition of the nitrided layer were investigated and analyzed using scanning electron microscopy (SEM) and X-ray diffraction (XRD), and we performed Vickers hardness and wear resistance tests using the ball-on-disc method. The microhardness and wear resistance of nitrided 40CrNi steel were significantly improved due to the lubricating properties of the ε-Fe₂N phase formed on its surface. Full article

Electronic components assembled in satellites should be able to withstand the vibration, noise, and impact loads generated by space vehicles during launch. To simulate the impact loading in a laboratory environment, a pyroshock test simulates an impact load resulting from explosions during the stage and pairing separation of launch vehicles, which imposes significant stress on the components, potentially leading to failures and damage. To ensure component reliability before the flight model (FM) stage, where components are mounted on the actual launch vehicle and sent into orbit, a pyroshock test is conducted during the qualification model (QM) stage using identical parts and specifications. This process involves measurements of the acceleration induced by pyroshock to calculate the shock response spectrum (SRS) and evaluate the components’ reliability against the required SRS to confirm their ability to endure the shock and operate normally in post-tests. The aerospace developer determines the SRS requirements based on the space launch vehicle and the installation location of the electronic components. Configuring a suitable pyroshock test to meet these requirements typically involves extensive trial and error. This study aims to minimize such trial and error by examination of SRS changes through a numerical approach by table structural vibration analysis. The structure is subjected to in-plane impacts using a steel ball via a pendulum method. Various SRS profiles are calculated by test factors such as the weight of the steel ball, the pendulum angle, and the installation position of the test specimen. Furthermore, a genetic algorithm is utilized to derive the optimal test conditions that satisfy the required SRS. An automated pyroshock test system is developed to enhance repeatability and reduce human errors. Full article

Grease lubrication is cost-effective and low-maintenance for motorized spindles, but standard steel bearings can fail at high speeds. This study focuses on high-speed full ceramic ball bearings lubricated with grease. The coefficient of friction torque in the empirical formula is corrected by establishing the heat generation model of full ceramic ball bearing and combining it with experiments. A simulation model of grease flow is established to study the influence of grease filling amount on grease distribution. The simulation model of the temperature field of a full ceramic ball bearing is established to analyze the influence of rotating speed on bearing heat generation, and experiments verify the calculation results of the theoretical model. The results show that an optimal grease filling amount of 15~25% ensures even distribution without accumulation. Additionally, when the amount of grease is constant, the outer ring temperature increases with higher rotating speeds. The test results show that when the grease filling is 0.9~1.2 g, it accounts for about 9~12% of the volume of the bearing cavity, and the temperature of the outer ring is the lowest. At a rotation speed of 24,000 rpm, the outer ring temperature of the grease-lubricated bearing is 50.1 °C, indicating a reasonable range for use in motorized spindles. It provides a theoretical basis for the optimization design of macro-structural parameters of full ceramic ball bearings in the future, which can minimize heat generation and maximize bearing capacity. Full article