Low Friction Coefficient Research Articles

Tribological performance and composition optimization of semi-metallic friction materials applied for carbon ceramic brake disc

The tribological performance of C/C–SiC paired semi-metallic brake pads suitable for automobiles was investigated in this study. Factors on tribological properties of semi-metallic brake pads such as the contents of phenolic resin, copper fibers, steel fibers and MoS2 were tested by the orthogonal experimental. According to the SAE-J2522 test procedure, an optimized compositional formulation was derived based on the brake test results combined with fuzzy comprehensive evaluation. The wear mechanism of brake pairs was discussed, and the compositional formulation of the brake pad was further optimized after the analysis of the friction surface morphology before and after braking. The results showed that copper fibers had the greatest effect on the friction performance of brake pads. Copper fibers contributed to stabilization of the coefficient of friction (COF) and effectively improved the wear resistance. However, at higher braking speeds (≥120 km/h), the copper fibers were converted from fibrous to flaky and softened, acting as a solid lubricant on the friction surface, resulting in a low COF of brake pads. The tribological performance of brake pads could be improved by reducing the content of copper fiber and increasing the content of hard particles.

Design of ternary solid lubricants SiO2/Ti3C2/PTFE for wear-resistant, self-lubricating polyimide composites

BackgroundPolyimide is widely used in aerospace, electronics and electrical appliances, automotive, chemical and other fields due to its high temperature stability, excellent mechanical properties. However, polymer materials are often subjected to severe wear and tear under complex operating conditions due to their poor lubrication performance. Therefore, the improvement of lubrication performance is a key strategy to extend the service life of polyimide. MethodsHerein, a ternary solid lubricant SiO2/Ti3C2/PTFE (STP) is innovatively prepared by solution dispersion for reducing the friction of polyimide to increase the lubricity. Specifically, SiO2 and PTFE are intercalated accordion-like Ti3C2 nanosheets, thereby causing the nanosheets to slide relative to each other under external frictional stress. Then, STP was introduced into polyimide to prepare the ultra-wear-resistant and self-lubricating composites by blending. Significant findingsThe results of the study showed that the STP significantly enhanced the lubrication properties of the composites, the lowest coefficient of friction (0.29) of the composites is 22.81 % lower than that of the polyimide. In addition, the inclusion of hybrids helps to form a transfer film, which effectively improves the abrasion performance of polyimide, and the lowest wear rate (0.18 × 10−5 mm3/(N·m)) was 93.35 % lower than that of polyimide.

Achieving synergistic improvement of wear and mechanical properties in Ti–6Al–4V alloy by multiple cryogenic treatment

Ti–6Al–4V alloy was subjected to cryogenic treatment at −196 °C followed by single and multiple treatment cycles. Compression tests revealed that, despite a decrease in yield strength, cryogenically treated samples (especially by multiple cryogenic treatment) exhibited noteworthy improvements, with a 10.2% failure strain and 9.4% rise in compressive strength compared to the as-received state. The cryogenically treated samples were further refined and exhibited a reduced β-phase volume fraction, showed higher dislocation density and microstrain in X-ray diffraction results. Remarkably, the surface hardness was significantly improved by the cryogenic treatment, leading to enhanced wear resistance with lower coefficients of friction. This was attributed to the formation of smaller wear debris and a decrease in abrasive wear under sliding conditions. Electron backscatter diffraction (EBSD) findings demonstrate that the friction-induced localized deformation layers exhibit the high density of low angle grain boundaries (LAGBs) with deformation-induced sub-grains. The synergistic improvement of wear resistance and mechanical properties is ascribed to the intricate microstructural alterations induced during cryogenic treatment, particularly accentuated in multiple cryogenic treatment. These findings highlight the efficacy of cryogenic treatment in improving both mechanical and wear properties of Ti–6Al–4V alloy.

Enhanced high-temperature tribological performance of fluorinated tetrahedral amorphous carbon (ta-C:F) coatings in sliding applications

This study investigated the dry sliding behaviour of fluorinated tetrahedral amorphous carbon (ta-C:F) coatings against uncoated 52100 steel at temperatures ranging from 25 °C to 300 °C. The ta-C:F coatings demonstrated significant reductions in both the coefficient of friction(COF) during the running-in stage and at steady state, particularly within the temperature range of 25 °C to 200 °C, surpassing the performance of well-established a-C:H coatings. SEM analyses revealed the formation of transfer layers on the contact surface of 52100 steel when tested against ta-C:F coatings at temperatures up to 200 °C, while none were detected at temperatures ≥250 °C. Raman spectroscopy indicated a transition from sp3 to sp2 carbon structures in the carbonaceous transfer layers with increasing temperature, and XPS scans confirmed an increase in fluorine (F) concentration within these layers, correlating with reduced COF. The comparative analysis at 120 °C emphasized the intrinsic advantages of ta-C:F coatings in high-temperature applications, demonstrating a nearly 50% lower COF (0.08) when compared to traditional boundary-lubricated steel-to-steel sliding contacts. These findings have significant implications for enhancing the efficiency and durability of various mechanical systems, particularly in industries like automotive and manufacturing.

Investigation on tribological characteristics of Al 7075 coated with aluminium chromium nitride (AlCrN) by magnetron sputtering

Structural components used in aerospace, automotive, and civil applications should have an increased shelf life. Fretting wear occurring in aluminum alloys decreases the reliability of the components. This study presents the investigations of tribological characteristics of Al7075, coated with Aluminium Chromium Nitride (AlCrN) by Physical Vapor Deposition (PVD) magnetron sputtering technique. Although Al7075 possesses a high strength-to-weight ratio, it has inadequate resistance against fretting wear. The experimental findings of the wear test (Pin on Disc) reveals that AlCrN coating on Al7075 increases the wear resistance and exhibits a low coefficient of friction. A thin film coating of AlCrN given on Al7075 enhances its tribological and corrosion properties. The existence of AlCrN coating composition on the substrate is confirmed by the results of Energy Dispersive Spectroscopy (EDX). Crystal structural phase analyzed using X-ray diffraction (XRD) shows Face Centered Cubic (FCC) structure for coated Al7075 samples. The pin-on-disc test results show that the wear rate has reduced for coated samples. A salt spray corrosion test is executed to evaluate the corrosion rate for 24 h. When comparing coated samples to uncoated samples, it is found that the corrosion rate is lower for coated samples. The average hardness value of the coated Al7075 sample is higher than the uncoated ones. The surface roughness of the coated sample is observed to be less than that of uncoated Al7075 samples.

Investigation of Wear Properties and Corrosion Resistance of Electrodeposited Ni-P-PTFE Nanocomposite Coating on Mg-Li alloy

Ni-P-polytetrafluorethylene nanocomposite coatings based on Mg-Li alloy were successfully prepared by utilizing electrodeposition method. The nanocomposite coatings were investigated employing scanning electron microscopy, atomic force microscopy, and X-ray diffraction. The microstructure and composition of the coating were studied by friction, wear and corrosion tests. The experimental results reveal that when the concentration of PTFE is 3 g / L, deposition temperature is 70 °C, current density is 2 A/dm2, and pH of the plating solution is approximately 5.5, a uniform and dense Ni-P-PTFE nanocomposite coating is formed on Magnesium alloy substrate, and it exhibited a low coefficient of friction (∼1.5) and superior abrasion resistance. The co-deposition of PTFE particles can effectively reduce the friction coefficient and wear rate, and the wear mechanism is characteristic cutting wear. Under artificial seawater conditions, the experiments have demonstrated that the nanocomposite material possesses a corrosion current density of 3.9×10-5 A/cm2.

Enhancing amorphous carbon wear resistance at high contact stresses through Ag incorporation

High load capacity is desirable in various industrial applications, such as gudgeon pins, cam followers, gears and bearings. Amorphous carbon (a-C) coatings, known for their minimal friction and low wear rates, have found extensive application in automotive components. However, the a-C films often fail at high contact stress (>2 GPa). Extensive efforts have been devoted for the application of a-C under high contact stress, and a few groups can prevent the sudden failure of a-C in high load condition up to now. Nevertheless, the wear rate is still high, which is in the range of ∼10−7 mm3/Nm, at least ten times greater than that of films under low stresses (<2 GPa). To tackle this issue, Ag-C supra-nano-dual-phase composite (SNDP) was fabricated using magnetron sputtering (‘supra-nano-dual-phase’ means the diameter of each phase is smaller than 10 nm). Various methods were employed to examine the structural features, mechanical attributes, and tribological performance of Ag-C SNDP. The research revealed that Ag nanocrystals, ranging in size from 2 to 4 nm, were uniformly incorporated within the amorphous carbon matrix. The Ag-C SNDP film with 4.0 at.% Ag shows an order of magnitude lower than amorphous carbon (a-C) at wear rate. It also pushes the load-bearing capacity as high as 4.0 GPa, which has rarely been reported before. The superior tribological behavior of Ag-C SNDP composite can be explained in three factors: (1) the ‘supra-nanometer-sized dual-phase’ structure provides adequate strength; (2) the surface graphitization within several nanometers from the surface enables low friction coefficient and prevents sudden failure; (3) incorporating Ag into the films resulted in a reduction in residual stress and an increase in film toughness.

ADAPTIVE DLC COATINGS WITH DIFFERENT MoS2 CONTENT

DLC coatings are widely used in engineering as they are resistant to abrasive wear. However, they exhibit anincreased coefficient of friction at temperatures of around 300C. Soft MoS2 coatings are known to maintaina low coefficient of friction at temperatures up to about 350C, but suffer from relatively high abrasive wear.Publications from the last decade report a synergistic improvement in the tribological performance of acoating consisting of both these materials. The aim of this study was to investigate the wear resistance ofcoatings composed of different a-C and MoS2 contents applied by magnetron sputtering on steel. The resultsobtained in tribological tests conducted using the ball-and-disk method showed at least 20% better adhesionto the substrate of the two-component nanocomposite coating and its increased wear resistance from 15% toas much as 700%, compared to single-component coatings in tests conducted at 20C and 250C. The testsshowed no deterioration of the two-component coating's coefficient value compared to DLC.

Vertical and Horizontal Double Gradient Design for Super‐Slippery and High‐Bearing Hydrogel Skeleton

AbstractHydrogels with excellent hydrophilicity, high water content, outstanding biocompatibility, and lubrication properties are among the promising articular cartilage replacement materials. Despite extensive research focus on lubrication of hydrogels, realization of bioinspired materials with high load‐bearing, low‐friction, extraordinary lubrication, and anti‐wear properties is challenging. Herein, robust lubrication can be realized by structuring vertical and horizontal dual gradient surfaces, with structural design in vertical direction gradually transitioning from an anisotropic tubular to a compact body to provide load‐bearing, and a surface rigid porous polymer skeleton and a filled loose lubricating polymer structural design to provide lubrication in horizontal direction. What is more, gradient transition region in vertical direction greatly weakens gradient layer interface stress to increase load‐bearing, and gradient surface in horizontal direction is constructed by interconnected surface rigid polymer skeleton containing “pockets” that house highly hydrated and mechanically fragile soft lubrication polymer to prevent removal of lubrications under high load and wear. The designed hydrogel has an extremely low coefficient of friction (COF) with hard steel (COF ≈0.0036, 50 N, 35,000 cycles) and achieves a balance between lubrication and load bearing. The work opens up an avenue for rational design of high load‐bearing and ultralow friction soft material surfaces.

TRIBOLOGICAL PROPERTIES OF A SILICONE-BASED COMPOSITEWITH INORGANIC ADDITIVES

The paper presents the results of experimental studies, including tribological tests of silicone-based compositeswith additions of hexagonal boron nitride (hBN) and titanium (Ti). The tests were conducted on a BrukerUMT2 tribotester and using a pin-on-disk setup developed by the authors, without a lubricating medium,and they employed a steel ball made of 100Cr6 steel and a sample made of the composite. During the tests,the products were not removed from the contact area. The paper analyzes the influence of additives on thetribological properties of the composite, i.e., the coefficient of friction (COF) as a function of distance and thewear of the tested samples. In the case of samples containing hBN, the COF decreases with an increase in itscontent. After reaching a volumetric percentage concentration of 20%, it begins to stabilize with the increasein mass loss. The profiles of COF changes as a function of distance for samples with different additivecontents are comparable. The self-lubricating properties of hBN have been confirmed. The addition of Tireduces the COF value, which decreases with the increase in the Ti content. Samples with a mass percentageconcentration exceeding 100% of the Ti content have a COF value equal to the initial value for silicone. Thecomposite containing hBN has a lower COF value than samples with the Ti addition, and the wear tracks ontheir surface are narrower and shallower.

Bias voltage influence on the a-SiCx:H interlayer deposition using tetramethylsilane: Decorative applications of a-C:H thin films on steel

Hydrogenated amorphous carbon (a-C:H) is a type of coating vastly applied on steel alloys due to its low friction coefficient, high hardness, and chemical inertness. Also, its characteristic brilliant black color like onyx stone is desirable for decorative applications. Despite the beneficial properties conferred to ferrous substrates, the adhesion of a-C:H films is weakened by its residual stress. In order to improve the adhesion of a-C:H films/steel alloy structures, one adopted strategy is the addition of an interlayer. This research investigated the influence of the bias voltage applied on the deposition of hydrogenated amorphous silicon carbide (a-SiCx:H) interlayers, with tetramethylsilane (TMS) as the precursor, to promote adhesion in a-C:H/a-SiCx:H/ferrous alloy structures for decorative applications. The thicker interlayer was achieved at −600 V. Two regimes were proposed to explain this behavior considering ionization rates and resputtering rates and chemical reactions in plasma. The chemical structure in different regions of the a-SiCx:H interlayer was analyzed in detail. An increase in the applied bias voltage leads to oxygen incorporation at the a-C:H/a-SiCx:H interface. Higher bias voltages result in lower silicon content at the a-SiCx:H/steel interface, which is correlated to the −800 V sample’s poor adhesion. Finally, we have included a discussion about a new range of loads when a decorative piece is held by the hand where the critical loads for delamination of a-C:H coatings measured here are good enough for decorative applications.

High-density zwitterionic polymer brushes exhibit robust lubrication properties and high antithrombotic efficacy in blood-contacting medical devices

High-performance catheters are essential for interventional surgeries, requiring reliable anti-adhesive and lubricated surfaces. This article develops a strategy for constructing high-density sulfobetaine zwitterionic polymer brushes on the surface of catheters, utilizing dopamine and sodium alginate as the primary intermediate layers, where dopamine provides mussel-protein-like adhesion to anchor the polymer brushes to the catheter surface. Hydroxyl-rich sodium alginate increases the number of grafting sites and improves the grafting mass by more than 4 times. The developed high-density zwitterionic polymer brushes achieve long-lasting and effective lubricity (μ<0.0078) and are implanted in rabbits for four hours without bio-adhesion and thrombosis in the absence of anticoagulants such as heparin. Experiments and molecular dynamics simulations demonstrate that graft mass plays a decisive role in the lubricity and anti-adhesion of polymer brushes, and it is proposed to predict the anti-adhesion of polymer brushes by their lubricity to avoid costly and time-consuming bioassays during the development of amphoteric polymer brushes. A quantitative influence of hydration in the anti-adhesion properties of amphiphilic polymer brushes is also revealed. Thus, this study provides a new approach to safe, long-lasting lubrication and anticoagulant surface modification for medical devices in contact with blood. Statement of significanceHigh friction and bioadhesion on medical device surfaces can pose a significant risk to patients. In response, we have developed a safer, simpler, and more application-specific surface modification strategy that addresses both the lubrication and anti-bioadhesion needs of medical device surfaces. We used dopamine and sodium alginate as intermediate layers to drastically increase the grafting density of the zwitterionic brushes and enabled the modified surfaces to have an extremely low coefficient of friction (μ = 0.0078) and to remain non-bioadhesive for 4 hours in vivo. Furthermore, we used molecular dynamics simulations to gain insight into the mechanisms behind the superior anti-adhesion properties of the high-density polymer brushes. Our work contributes to the development and application of surface-modified coatings.

Enhanced Vehicle Dynamics and Safety through Tire–Road Friction Estimation for Predictive ELSD Control under Various Conditions of General Racing Tracks

This study focuses on the tire–road friction estimation for the predictive control strategy of electronically limited slip differential (ELSD) to improve the handling and acceleration performance of front-wheel drive cars, which typically suffer from excessive understeer and inner drive wheel spin during acceleration while turning due to reduced vertical load on the wheel. To mitigate this, we propose a control logic for ELSD that enhances course followability and acceleration by pre-transferring the driving torque from the inside to the outside wheel, considering the estimated traction potential for rapid response. It is essential to improve the control accuracy of wheel spin prediction by predicting the friction coefficient of the road surface. Furthermore, this study extends to the analysis of vehicle dynamics during lane-change maneuvers on low-friction surfaces, emphasizing the role of accurate tire–road friction estimation in vehicle safety. A CarSim 2023-based simulation study was conducted to investigate the vehicle response on snowy roads with low friction coefficients (μ = 0.2) and low temperatures (−5 °C). The results demonstrated that even minimal steering input could result in significant side-slip angles, highlighting the nonlinear vehicle behavior and the critical need for robust traction estimation in such challenging conditions of general racing tracks. The proposed friction-estimation method was evaluated through vehicle testing and has been substantiated by patents for its originality in control and friction-estimation approaches. The outcomes of these combined methodologies underline the critical importance of tire–road friction coefficient estimation in both the effectiveness of the ELSD system and the broader context of active safety systems.

High temperature tribological response of Fe-2Cu-0.8C-CaF2 self-lubricating composites at high speeds

In this work, Fe-2Cu-0.8C-CaF2 self-lubricating composites with calcium fluoride solid lubricant (3 □ 12 wt.%) were examined for their friction and wear at 5 and 10 m/s, at 500 °C. Addition of CaF2 decreased density and hardness of composites. During sliding, materials gained weight due to oxidation. Compared to the base matrix (Fe-2Cu-0.8C), composites showed lower weight gain and lower coefficient of friction. Increase in porosity with CaF2 content increased oxidation resulting in higher weight gain and increased friction due to wear debris abrasion. Increase in speed reduced weight gain due to higher material loss. Adhesion was the dominant wear mechanism in base matrix; delamination and wear debris abrasion in composites. Temperature rise at sliding surfaces was theoretically estimated. Increase in speed increased temperature, which reduced friction due to softening and shearing of solid lubricant. Composite with 3 wt.% CaF2 showed least surface damage and 6 wt.% showed lowest coefficient of friction, i.e., lower by 16% and 10% at 5, 10 m/s than base matrix. Tribological response of the composites to a broad range of applied parameters, viz. speed, load and temperature taken from earlier works and present work is briefly summarized. The study suggests the dominant role of CaF2 content and the wear debris in altering the tribological response. Further, the stability of the developed composites at high temperature and high load conditions was also established. The study suggests that the developed composites could serve high-load and high-temperature applications for heavy machinery such as bearings, shafts and gears.

Impact of faults on the remote stress state

Abstract. The impact of faults on the contemporary stress field in the upper crust has been discussed in various studies. Data and models clearly show that there is an effect, but so far, a systematic study quantifying the impact as a function of distance from the fault is lacking. In the absence of data, here we use a series of generic 3-D models to investigate which component of the stress tensor is affected at which distance from the fault. Our study concentrates on the far field, located hundreds of metres from the fault zone. The models assess various techniques to represent faults, different material properties, different boundary conditions, variable orientation, and the fault's size. The study findings indicate that most of the factors tested do not have an influence on either the stress tensor orientation or principal stress magnitudes in the far field beyond 1000 m from the fault. Only in the case of oblique faults with a low static friction coefficient of μ=0.1 can noteworthy stress perturbations be seen up to 2000 m from the fault. However, the changes that we detected are generally small and of the order of lateral stress variability due to rock property variability. Furthermore, only in the first hundreds of metres to the fault are variations large enough to be theoretically detected by borehole-based stress data when considering their inherent uncertainties. This finding agrees with robust stress magnitude measurements and stress orientation data. Thus, in areas where high-quality and high-resolution data show gradual and continuous stress tensor rotations of &gt;20∘ observed over lateral spatial scales of 10 km or more, we infer that these rotations cannot be attributed to faults. We hypothesize that most stress orientation changes attributed to faults may originate from different sources such as density and strength contrasts.

Enhancing structural replication of microfluidic chips: Parameter optimization and mold insert modification

AbstractThe demolding process in micro‐injection molding constitutes a critical phase, exerting a decisive influence on the quality of polymer microstructures. In this study, the demolding forces of PMMA microfluidic chips were measured under different demolding temperatures, packing pressures, and demolding speeds by using pure nickel (Ni) mold insert. The dimensional deviations of the microchannels with different aspect ratios were analyzed. In addition, the effect of mold insert modification on the demolding force was further analyzed. The results showed that the effect of demolding temperature on the demolding force was the most significant, and the peak demolding force decreased with the decrease in temperature. The width of the microchannels increased and the depth decreased after demolding, while the opposite results were observed for the micro‐mixing structures. However, the dimensional deviation of the micro‐mixing structures was larger than that of the microchannels. Using the optimal molding parameters, the peak demolding force could be reduced from 114.0 N at 110°C to 47.0 N, a decrease of 58.8%. It is noteworthy that, when the microchannel was narrower than 100 μm, achieving precise replication of microchannel dimensions became progressively more challenging as the microchannel width decreased. Using the Ni‐WS2 mold insert with low surface energy and low friction coefficient, the demolding force could be further reduced by 38.3%. The effect of the molding quality of microfluidic chip microstructures on the mixing performance of heavy metals was demonstrated by micro‐mixing experiments.Highlights Demolding temperature crucially affects microstructure dimensions. Optimal parameters and modified mold insert reduce demolding force by 38.3%. Dimensional deviation increases with the increase of microchannel aspect ratio. Optimized microfluidic chip enhances Co2+ chemiluminescence by 6.42%.

Microstructure and Properties of Aluminum-Graphene-SiC Matrix Composites after Friction Stir Processing.

Enhancing the mechanical properties of conventional ceramic particles-reinforced aluminum (Al 1060) metal matrix composites (AMCs) with lower detrimental phases is difficult. In this research work, AMCs are reinforced with graphene nanosheet (GNS) and hybrid reinforcement (GNS combined with 20% SiC, synthesized by shift-speed ball milling (SSBM), and further fabricated by two-pass friction stir processing (FSP). The effect of GNS content and the addition of SiC on the microstructure and mechanical properties of AMCs are studied. The microstructure, elemental, and phase composition of the developed composite are examined using SEM, EDS, and XRD techniques, respectively. Mechanical properties such as hardness, wear, and tensile strength are analyzed. The experimental results show that the GNS and the SiC are fairly distributed in the Al matrix via SSBM, which is beneficial for the mechanical properties of the composites. The maximum tensile strength of the composites is approximately 171.3 MPa in AMCs reinforced by hybrid reinforcements. The tensile strength of the GNS/Al composites increases when the GNS content increases from 0 to 1%, but then reduces with the further increase in GNS content. The hardness increases by 2.3%, 24.9%, 28.9%, and 41.8% when the Al 1060 is reinforced with 0.5, 1, 2% GNS, and a hybrid of SiC and GNS, respectively. The SiC provides further enhancement of the hardness of AMCs reinforced by GNS. The coefficient of friction decreases by about 7%, 13%, and 17% with the reinforcement of 0.5, 1, and 2% GNS, respectively. Hybrid reinforcement has the lowest friction coefficient (0.41). The decreasing friction coefficient contributes to the self-lubrication of GNSs, the reduction in the contact area with the substrate, and the load-bearing ability of ceramic particles. According to this study, the strengthening mechanisms of the composites may be due to thermal mismatch, grain refinement, and Orowan looping. In summary, such hybrid reinforcements effectively improve the mechanical and tribological properties of the composites.

Wear performance of short fiber added polyamide composites produced by additive manufacturing: Combined impacts of secondary heat treatment, reinforcement type, and test force

AbstractIn recent years, the number of studies focusing on the additive manufacturing has increased seriously to elucidate the critical points such as physical, chemical, and mechanical properties. Contrary to common trends and for the first time in the literature, this experimental endeavor aims to comprehend the combined impact of reinforcement type and heat treatment on the wear features of additively manufactured polyamide 6 (PA6) composites. As reinforcement materials, glass, and carbon fibers were utilized and all samples were created through the fused filament fabrication. Half of the samples were subjected to annealing treatment after the main production, and characterization works were performed using a fused emission scanning electron microscope, differential scanning calorimetry, and dynamic mechanic analysis. From the outcomes, it is seen that heat treatment has a positive effect on the hardness, and wear resistance of the composites. Besides, glass fiber‐reinforced samples display lower friction coefficient and lower volume loss results than other samples. For all samples, secondary annealing causes a positive impact on wear endurance in most cases. On the other side, the wear mechanism of the tested samples changes with the test force level and reinforcement type. At lower test forces, abrasive wear‐induced debris parts are detected on the deformed surfaces of PA6 and carbon‐added samples, but this case is opposite for the highest force of 40 N.Highlights Additive manufacturing was underlined as a promising way to create polymer composites with high dimensional accuracy. The combined effect of secondary annealing and reinforcement type on the wear resistance of 3D‐printed PA6 composites was examined for the first time in the literature. Carbon and glass fibers were compared to explore their effect on friction coefficient and wear behavior of polymer composite samples produced via FFF technology. Hardness and surface roughness measurements were used to comprehend the dry sliding wear results. Depending on the increasing test force levels and reinforcement type, deformation, and abrasion mechanisms were analyzed.

Effect of squamous textured SiC on the dry-sliding tribological properties of graphite asperities

The graphite rough morphology influences the operating performance of the sealing surface. Texturing silicon carbide surfaces can considerably improve the tribological characteristics of sealing surface. Herein, a fractal model was established to study the contact and tribological characteristics of graphite asperities, and the pin-on-disk wear tests were conducted to investigate the influence of squamous texture on graphite asperities under dry-sliding condition. Results indicated that reducing the graphite surface roughness decreases the contact area to decrease the friction coefficient. The squamous texture increases the deformation and contact area of graphite asperities. But the wear debris collection of the squamous texture prevents the adhesive wear, and the microcutting effect promotes the formation of graphite transfer film on the silicon carbide surface. Therefore, the squamous texture has the low friction coefficient and excellent worn morphology. Especially, under the high load of 80 N, combining the textured silicon carbide with the optimal graphite surface roughness of 0.14 μm exhibits a synergistic anti-friction effect that the friction coefficient reduced by 19%.

Construction methods and biomedical applications of PVA-based hydrogels.

Polyvinyl alcohol (PVA) hydrogel is favored by researchers due to its good biocompatibility, high mechanical strength, low friction coefficient, and suitable water content. The widely distributed hydroxyl side chains on the PVA molecule allow the hydrogels to be branched with various functional groups. By improving the synthesis method and changing the hydrogel structure, PVA-based hydrogels can obtain excellent cytocompatibility, flexibility, electrical conductivity, viscoelasticity, and antimicrobial properties, representing a good candidate for articular cartilage restoration, electronic skin, wound dressing, and other fields. This review introduces various preparation methods of PVA-based hydrogels and their wide applications in the biomedical field.