Low Wear Resistance Research Articles

Effect of 3D printing system and post-curing atmosphere on micro- and nano-wear of additive-manufactured occlusal splint materials

Although additive manufacturing has been widely applied for occlusal splint (OS) fabrication, it is still unclear whether 3D printing system and post-curing atmosphere would play a role in the wear resistance of additive-manufactured OS. Therefore, the aim of this study was to evaluate the effect of 3D printing system (liquid crystal display (LCD) and digital light processing (DLP)) and post-curing atmosphere (air and nitrogen gas (N2)) on the wear resistance of hard and soft OS materials for additive-manufactured OSs (KeySplint® Hard and Soft). The evaluated properties were microwear (by two-body wear test) and nano-wear resistances (by nanoindentation wear test) as well as flexural strength and flexural modulus (by three-point bending test), surface microhardness (by Vickers hardness test), and nanoscale elastic modulus (reduced elastic modulus) and nano surface hardness (by nanoindentation test). For the hard material, the surface microhardness, microwear resistance, reduced elastic modulus, nano surface hardness, and nano-wear resistance were significantly affected by the printing system (p < 0.05), while all the evaluated properties except flexural modulus were significantly affected by the post-curing atmosphere (p < 0.05). Meanwhile, both the printing system and post-curing atmosphere significantly affected all the evaluated properties (p < 0.05). The specimens additive-manufactured by DLP printer tended to show higher wear resistance in the hard material groups and lower wear resistance in the soft material groups when compared to those by LCD printer. The post-curing at N2 atmosphere significantly enhanced the microwear resistance of hard material groups additive-manufactured by the DLP printer (p < 0.05) and soft material groups additive-manufactured by the LCD printer (p < 0.01), while it significantly enhanced the nano-wear resistance of both hard and soft material groups regardless of the printing system (p < 0.01). It can be concluded that 3D printing system and post-curing atmosphere affect the micro- and nano-wear resistance of tested additively manufactured OS materials. In addition, it can be also concluded that the optical printing system providing higher wear resistance depends on the material type, and using nitrogen gas as a protection gas during post-curing enhances the wear resistance of tested materials.

Investigating Mechanical and Wear Properties of CaCO3 Filled PP Composite Filament Production for 3D Printer

Recently, the interest in 3D printers, which is one of the polymer-based material production methods, and the amount of production in the sector are increasing day by day. It is clearly seen that 3D printers, which were used as hobby devices in the beginning, have evolved from being hobby devices to industrial production devices. When current studies are examined, it is clearly observed that 3D printers not only uses pure polymers, but also usage of composite materials has begun. In this study, Pure PP and various weight filling ratio CaCO3 filled PP composite flaments were produced. Wear test and three-point bending test specimens were produced with the produced filaments on the 3D printer and tested. When the Mechanical Test results were examined, it was determined that the flexural strength of the composite samples was affected adversely. The wear test results showed that the particle reinforcement reduced the friction coefficient by making a lubricating effect on the surface. The wear volume of the composite samples decreased by approximately 40% compared to pure PP. As a result, it has been seen that it can be produced with composite filament in applications requiring low friction and high wear resistance, where the mechanical strength can be waived to a certain extent. Especially when it is considered that there is a ratio of approximately 1/10 between the prices of matrix and reinforcement materials, composite filament gains more importance in order to reduce the cost of the final product.

Achieving well-balanced mechanical and tribological properties of copper matrix self-lubricating composites by adding pre-metallized B4C particles with core-shell microstructure

Copper matrix self-lubricating composites have the advantage of low friction coefficient, but usually suffer from the low mechanical strength, ductility and wear resistance. Ceramic particles reinforcing has been demonstrated an effective way in strengthening metal matrix composites. However, the poor wettability was always a critical issue. In this study, B4C particles were introduced into a copper matrix self-lubricating composite. Before spark plasma sintering, the B4C particles were pre-metallized with Ni to form a core-shell microstructure (Ni@B4C), which improves wettability and bonding strength with the copper alloy, builds up a coherent/semi-coherent interface, and notably enhances mechanical properties. After the incorporation of pre-metallized Ni@B4C particles, the compressive strength, hardness and engineering strain are increased by 62, 113 and 76%, respectively. What is more, the composite exhibits improved tribological performances. Owing to the successful transfer of lubricant WS2 to the wear surface during sliding as well as the greatly enhanced hardness, its friction coefficient is decreased to 0.16, while the wear rate is reduced to 7.53 × 10−6 mm3/N·m, which is 81% lower than that of CW. The composite achieves well-balanced mechanical and tribological properties after pre-metallized B4C particles incorporation.

The Electroless Monolayer and Duplex Ni–B and Ni–P Coatings for 316L Stainless Steel in Synergistic Combination of Mechanical (Wear) and Chemical (Corrosion) Processes

Conventional processes are performed to improve the low hardness and low wear resistance properties of 316L steel, but these processes generally decrease the corrosion resistance. Electroless nickel alloy coatings provide a hard, wear‐resistant, and corrosion‐resistant surface. Thus, the present study aims to investigate the wear, corrosion, and tribocorrosion behaviors of monolayer and duplex coatings with nickel–boron (Ni–B) and nickel–phospore (Ni–P) on 316L steel in comparison with 316L steel in dry sliding and 0.9 wt% NaCl solution environments. It is determined that the coatings have a mixture of crystal and amorphous structures, the interfaces on the 316L are uniform, and the compatibility between the layers is good. The Ni–B, Ni–P/Ni–B, and Ni–B/Ni–P coatings are 2.3, 2.06, and 1.6 times as hard as the 316L, respectively. The wear rates of Ni–B, Ni–P/Ni–B, and Ni–B/Ni–P coatings show decrease by 99.3%, 92.5%, and 99.1% in the dry‐sliding condition and by 98.5%, 30.1%, and 19.1% in the tribocorrosion condition compared with that of 316L, respectively. It is observed that the monolayer Ni–B coating exhibits superior hardness, a higher contact angle, low electrical conductivity, and better tribological performance in both dry sliding and tribocorrosion conditions compared to the 316L and duplex coatings.

Clinical comparison of different glass ionomer-based restoratives and a bulk-fill resin composite in Class I cavities: A 48-month randomized split-mouth controlled trial

ObjectiveThe aim of this study is to compare the retention rates (primary outcome) of high-viscosity glass ionomer (GI), glass carbomer (GC), zirconia-reinforced GI (ZIR), and bulk-fill (BF) composite resin restorations. Secondary outcomes included anatomical form, marginal adaptation, marginal discoloration, color match, surface texture, post-operative sensitivity and secondary caries. MethodsTwo calibrated operators placed 128 restorations in 30 patients with a mean age of 21 years. The restorations were evaluated by one examiner at baseline and at 6, 12, 18, 24, and 48 months using the modified US Public Health Service criteria. The data were statistically analyzed using Friedman test. Differences between restorations were analyzed using Kruskal–Wallis test. ResultsAfter 48 months, 23 patients and 97 restorations (23 GI, 25 GC, 24 ZIR, and 25 BF) were evaluated. Patient recall rate was 77%. No significant difference was observed between the retention rates of the restorations (p > 0.05). GC showed significantly lower results than the other three fillings in terms of anatomical form (p < 0.05). There was no significant difference in the anatomical form and retention between GI, ZIR, and BF (p > 0.05). No significant change was observed in the postoperative sensitivity or secondary caries for any of the restorations (p > 0.05). ConclusionsGC restorations showed statistically lower anatomical form values, indicating lower wear resistance than the other materials. However, no significant difference was observed in the retention rates (as primary outcome) as well as the other secondary outcomes of the four different restorative materials after 48 months. Clinical SignificanceGI-based restorative materials and BF composite resin restorations in Class I cavities yielded satisfactory clinical performance after 48 months.

Comparison of the surface morphologies of ceramic reinforced metal matrix composite cams after wear tests under dry and wet conditions

The integral engine parts, such as camshaft members, are usually not preferably made of ceramic-reinforced MMC because the margin of compromise on the engine performance is small. However, the lightweight and wear-resistant nature of the mentioned materials can benefit fuel consumption without necessarily compromising engine performance. In this study, Al (AA2124) matrix is reinforced with ceramic particles of two different types (SiC, B4C), size distributions (B4C: 1–7, SiC: 2 and 20 μm), and volume fractions (0, 10, 20, 30 vol.%) to manufacture camshaft cams (lobes). While MMC cams are manufactured by powder metallurgy (300 MPa, 615°C, 30 minutes), spherical graphite cast iron (GGG40) cams are prepared by casting, induction hardening, and machining. The wear behavior of MMC cams is compared with the reference unreinforced AA2124 and conventionally used cast iron cams under dry and virtually created engine-like wet conditions. It was attempted to correlate the percentage increase in the roughness and weight loss with the structure of the cams using SEM, EDX, and macroscopy analysis. Results showed that the initiation of a three-body abrasive wear mechanism for 30 vol.% of the larger SiC particles caused lower wear resistance in the cams under dry conditions. As for the wet conditions, although the cams’ wear resistance increased with increasing ceramic particles’ content, it resulted in enhanced wear in the counterface when larger ceramic particles were used as reinforcement. Overall, higher ceramic content and larger particle size encourage three-body abrasive wear between the interacting surfaces and assist in degraded wear resistance under wet conditions.

The Effect of Heat Treatment on the Structural-Phase State and Abrasive Wear Resistance of a Hard-Anodized Layer on Aluminum Alloy 1011

The aim of this study was to evaluate the effect of heat treatment on the phase composition, hardness, and abrasion wear resistance of hard-anodized layers (HAL) on 1011 aluminum alloy. X-ray diffraction analysis revealed the Al2O3·3H2O phase in the structure of HAL synthesized for 1 h. While in the heat-treated HAL, aluminum oxide phases of the α-Al2O3(amorphous) and γ-Al2O3(amorphous) types were found. Treatment at 400 °C for 1 h increased the HAL microhardness from 400 to 650 HV, and its abrasive wear resistance with fixed abrasive by up to 2.6 times. The ranking of various ways of hardening aluminum alloys relative to the D16 alloy showed that the abrasive wear resistance of heat-treated HAL is 20 times higher. Plasma electrolyte oxidation increased the abrasive wear resistance of the D16 alloy by 70–90 times, and its coating with high-speed oxygen fuel by 75–85 times. However, both methods are complex, energy-consuming, and require fine grinding of parts. Despite the lower wear resistance of HAL, their synthesis is cheaper and does not require the fine-tuning of parts. Moreover, despite the low hardness of HAL at present, hard anodizing is already commercially used to harden engine pistons, clamshell rotators, and pulleys.

Microstructure-property evolution of mechanically alloyed Al-20 wt% Si matrix powders and sintered composites reinforced withTiB2 particulates

Microstructural, physical and mechanical properties of Al–20 wt% Si matrix alloy powders and those reinforced with TiB2 and their sintered composites were investigated in relation to TiB2 content and mechanical alloying (MA) durations. Al–20 wt% Si matrix alloy powders and those containing 5 and 10 wt% TiB2 reinforcing particles were MA’d for 1, 2, 4, and 8 h followed by consolidation and sintering at 843 K. Si solubility in a-Al matrix increased with increasing MA duration. Increasing the TiB2 content, on the other hand, resulted in a systematic drop in Si solubility over the same MA period. Scanning electron micrographs of the sintered samples revealed sub-micron-sized, rod-shaped Si and spherical Al9Si phase particles. With increasing TiB2 content and MA durations, the microhardness of the Al20Si/TiB2 composites improved. The wear resistances of TiB2 reinforced composites better by 5 to 8 times than that of the as-blended and 1 h MA’d AlSi matrix alloy. Due to the presence of the Al3Ti intermetallic phase, sintered composite samples containing 10 wt% TiB2 particles MA'd for 8 h had the maximum hardness value and lower wear resistance values than those of the Al–20 wt% Si/5 wt% TiB2 composites.

Antibacterial and Virucidal Evaluation of Ultrafine Wire Arc Sprayed German Silver Coatings.

The online version contains supplementary material available at 10.1007/s11666-022-01528-4.

Influence of hybrid nanoparticles on the wear behavior of aluminum alloy composites for aerospace applications

PurposeEngineers and scientists are searching for novel materials with high performance on all aspect points of view for the applications including marine, aero and automobile fields. AA8090 aluminum alloy is one of the materials used in aero industries for aircraft construction because of its weight reduction ability. However, the AA8090 alloy has a drawback such as low wear resistance that affects the life time of material; hence, it should be addressed. The purpose of this investigation is to improve the wear resistance of AA8090 alloy.Design/methodology/approachIn this investigation, AA8090 aluminum alloy metal matrix composite was fabricated using different types of carbide nanoparticles such as vanadium carbide (VC), Cr3C2 and Mo2C by stir casting method and tribological and mechanical behaviors were studied.FindingsMechanical studies showed that the S1 sample displayed the maximum hardness of 142 HV and maximum tensile strength of 857 MPa because of the inclusion of hard VC particles. Tribological studies revealed that S1 sample showed high performance. A least wear rate of 0.003915 × 10–3 mm3/m was noted for S1 sample, which is 71% lower than the wear rate of S0 sample. Further, a least mass loss and lower coefficient of friction of 0.00152 g and 0.2, respectively, were observed for S1 sample because of its high hardness and high wear resistance because of the stuffing of high-hardness VC particles. Hence, it is concluded from this study that S1 sample, i.e. AA8090/VC, could be a better candidate for aerospace applications as it showed good tribological and mechanical properties.Originality/valueTo the best of the authors’ knowledge, this work is original and novel in the field of metal matrix composite which deals with the effect of hybridization on the wear performance of the aluminum alloy composites.

Дослідження впливу температури електроліту при імпульсному анодуванні на властивості поверхневих шарів технічного алюмінію

luminum alloys are characterized by low abrasive wear resistance, which significantly restricts their wide use in technological environments, especially if they contain abrasive particles. The method of pulse anodizing, which consists in periodically changing the current density, allows to improve the hardness and abrasive wear resistance. However, the influence of temperature on these processes has not been sufficiently studied. The process of pulsed hard anodizing was carried out in a 20% aqueous H2SO4 solution at a current density of 1.4 A/dm2 with a frequency of 100 Hz and a sparability of 75%. The temperature of the electrolyte during the formation of layers was maintained at -5°±1С, 0°С±1, +5°С±1, +10°С±1. The duration of synthesis was 60 minutes. At low temperatures of less than -5С due to the low speed of electrochemical processes, oxide layers with reduced microhardness and thickness are synthesized. At the same time, the phase analysis recorded the synthesis of an oxide layer based on aluminum with the content of two phases: the synthesis of the anodized layer begins with the formation of hydrated aluminum oxide Al2O3•H2O. As the anodizing temperature increases, the rate of electrochemical processes increases, which leads to an increase in the thickness of the anodized layer and its microhardness. At temperatures of 0С and -5С, the anodized layer contains only one phase - Al2O3 H2O, (boehmite) with one water molecule. At anodizing temperatures of +5С and -8С, the anodized layer is formed again in the form of two phases - Al2O3 3H2O (gibbsite) and Al2O3H2O (boehmite) and at a temperature of +10С only Al2O3 3H2O (gibbsite). At a temperature lower than –10°C, the electrolyte turns into a gel-like substance in which electrochemical reactions practically stop, so the synthesis of a pulsed solid anodized layer at a temperature of –5°C was started. However, as a result of the synthesis at T = –5 С and then even higher (up to 0С), the average thickness of the pulsed hard anodized layer increased from 83 μm to 110 μm. With further increase in the temperature of the electrolyte, the thickness decreased and at an electrolyte temperature of +10 С it was 80 μm. Such a change in the thickness of the anodized layer depending on the synthesis temperature was explained by two opposing processes that occur during anodization. As the temperature of the electrolyte increases, the process of synthesis of the layer intensifies first of all, and therefore the thickness of the obtained layer should constantly increase with the increase of the synthesis temperature. However, an increase in the temperature of the electrolyte also intensifies the surface dissolution of the anodized layer, which is aimed at reducing the thickness of the anodized layer. And when the rate of dissolution of the anodized layer begins to exceed the rate of its synthesis, its thickness begins to decrease. Conclusions: 1) The more water and sulfur molecules in the anodized layer, the lower its microhardness and abrasive wear resistance. 2) The minimum wear of the anodized layer, which means the highest wear resistance, was recorded for layers synthesized at an anodization temperature of -8ºС, and the maximum wear and lowest wear resistance at an anodization temperature of -5ºС. 3) High wear resistance of anodized layers synthesized at electrolyte temperatures from -8 to +10ºС under conditions of friction without lubrication is caused by the presence of crystalline water in the anodized layer.

Мікроструктура поверхневого шару титанового сплаву модифікованого вакуумним іонним азотуванням в імпульсному режимі

The mechanical strength and durability of structural elements is ensured by the correct selection of the materials from which they are made and the special functional properties of the surface layer, which are provided by applying coatings or by changing the structural state of the surface layers of the material by means of their modification. The use of titanium alloys provides unique properties, including high specific strength, corrosion resistance and a fairly high melting point. However, the use of these materials is limited by their low hardness, extremely low wear resistance, high tendency to sticking, high coefficient of friction in pairs with almost all materials, high chemical activity during heating above 500ᵒС and sensitivity to stress concentrators. To reduce the disadvantages of titanium alloys, various technological processes of strengthening are used by modifying the surface layers: by implantation of ions of various metals; surface treatment with concentrated energy flows; plasma flows; surface plastic deformation; ultrasonic treatment; laser processing; diffusion saturation and chemical-thermal treatment. Of all the modification methods, such a method of HTO as nitriding has become the most widespread, however, it involves long-term high-temperature heating, which causes fragility of the obtained nitrided layers, leads to a change in the metal structure and a decrease in strength characteristics. Task statement: conduct metallographic studies of the microstructure of modified surfaces with determination of the structure and depth of saturation of the diffusion layer with nitrogen Microsands for metallographic studies were produced on the "Alpha &amp; Beta" installation (manufacturer of TM BUEHLER) according to the standard method (preventing tempering and overheating) with subsequent detection of the microstructure by chemical etching in a herbarium: НNO3 : HF : H2O (7 ml. : 2 ml. : 50 ml.). Metalohrafichni doslidzhennya zrazkiv provodyly v pozdovzhnʹomu peretyni po tovshchyni na optychnomu invertovanomu mikroskopi «AXIOVERT 40 MAT» z fiksatsiyeyu mikrostruktur tsyfrovoyu fotokameroyu AXIOCAM 305 v prohrami «ZEN core v3.1» Yak pokazaly doslidzhennya, tovshchyna nitrydnoho sharu pry vakuumnomu ionnomu azotuvanni v impulʹsnomu rezhymi tytanovoho splavu VT1-0 skladaye ne bilʹshe 1520 mkm, pid yakym znakhodytʹsya zona vnutrishnʹoho azotuvannya menshoyi tverdosti, yaka postupovo zmenshuyetʹsya po eksponentsiyniy zalezhnosti do tverdosti osnovy. Metallographic studies of the samples were carried out in a longitudinal cross-section by thickness on an optical inverted microscope "AXIOVERT 40 MAT" with fixation of microstructures by a digital camera АXIOCAM 305 in the program "ZEN core v3.1". As the studies showed, the thickness of the nitride layer during vacuum ion nitriding in the pulse mode of titanium alloy VT1-0 is no more than 1520 μm, under which there is a zone of internal nitriding of lower hardness, which gradually decreases exponentially depending on the hardness of the base. The structure of the base material does not change during low-temperature nitriding. A nitrided layer is formed on the surface with a nitride zone of varying thickness, which depends on the mode of nitriding and is weakly etched by the herbarium. The microstructure of the samples is an equiaxed polyhedral structure of the α-phase with a liquation band in the axial zone. Microhardness was determined under a load of 50, 100, and 200 g. The holding time under the load was 10 seconds. Microhardness was measured on the sandpapers in the radial direction of the segment with a step of 0.05 mm. The load depended on the dispersion and thickness of the reinforced layer. Conclusions. Nitriding (up to 900ᵒС) in the glow discharge of titanium VT1-0 and VT1-00 allows to significantly increase the microhardness due to the properties of nitrogen and its compounds with titanium, while preserving the original mechanical properties of the base material. A change in the parameters of the nitriding process (temperature, pressure, composition of the saturating medium and nitriding time) causes a change in the physical and mechanical characteristics, structure, thickness, phase and chemical composition of the surface nitriding layer: microhardness of the surface up to 10500 MPa; the thickness of the nitrided layer is up to 500 microns; the thickness of the nitride layer is up to 25 microns; phase shift difference TiN, Ti2N, Ti(N); different gradient of hardness in depth, which allows to optimize the power of the surface of the ball in specific conditions of operation.

FRICTION PROPERTIES OF MАO COATINGS ON ALUMINUM ALLOYS

Aluminum alloys are widely used in mechanical engineering due to their physical and mechanical properties. However, their low wear resistance and burr resistance limit their use in friction nodes. In this regard, parts made of aluminum alloys operating under conditions of sliding friction require surface strengthening, which determines the friction wear parameters. Research works in this direction allow increasing the reliability and service life of friction nodes. Ensuring the compatibility of friction pairs allows reducing the coefficient of friction and, as a result, to increase wear resistance. One of the effective methods of forming wear-resistant coatings on aluminum alloys is the method of micro-arc oxidation (MAO). The use of micro-arc discharges as highly concentrated energy sources to create conditions for high-temperature electrotechnical processes and phase transformations in the surface layer makes it possible to form structures based on high-temperature oxides on the surface of metals, which provides qualitatively new surface properties: high hardness, wear resistance, corrosion resistance in various environments. However, the use of oxide coatings in bearings is mainly due to their high wear resistance and corrosion resistance. Information on the antifriction properties of aluminum oxide-based coatings is limited. The purpose of this work is to determine the coefficient of friction of MAO-coatings on D16 aluminum alloy in a pair with cast iron, steel and MAO-coating under conditions of oil and water lubrication, and to find out the feasibility of using MAO technology to create sliding bearings. The formation of MAO coatings was carried out in an alkaline-silicate electrolyte in the cathodic-anodic mode. The structure and morphology of the working layer of the MAO-coating surface, which works in friction pairs with cast iron, steel and MAO-coating under conditions of oil and water lubrication, was investigated. The benefit of the available porosity of the working layer of the MAO coating, which is 5-10% and contributes to the retention of lubricant in the friction zone, is shown. The phase composition, hardness of the coatings were studied and the coefficient of sliding friction was determined on the SMC-2 friction machine according to the "disk-pad" scheme when using water and oil as lubricants; the load varied from 0.2 to 2 kN, the nominal pressure from 1 to 11 MPa. It was established that the MAO coating has a crystalline structure, the phase composition is high-temperature modifications of aluminum oxide (α-Al2O3 and γ- Al2O3), and the hardness is 18000-20000 MPa. It was established that the coefficient of sliding friction of gray cast iron - MAO-coating, steel - MAO-coating and MAO on MAO decreases to the value of 0.01 - 0.013 under lubrication conditions. It was found that in a pair of MAO-coating - MAO-coating, anti-friction properties are manifested both under conditions of lubrication with oil and water. The low coefficient of friction for the coating-coating pair in the case of water lubrication is explained by the high hydrophilic properties of the oxide contacting surfaces, which makes it possible to recommend them for use in sliding bearings (liners) of hydroturbines. A conclusion was drawn regarding the reasons for the low coefficient of friction of the studied samples. Keywords: D16 aluminum alloy, cast iron, steel, micro-arc treatment, coating, phase composition, crystal structure, aluminum oxides, coating thickness, coating hardness, friction coefficient, antifriction properties

Ultralight Functionally Graded Hybrid Nanocomposites Based on Yttrium and Silica-Reinforced Mg10Li5Al Alloy: Thermal and Tribomechanical Properties.

Despite the amazing properties of lightweight Mg10Li5Al alloy, its use in industrial applications is highly limited due to its low mechanical properties, wear resistance, and coefficient of thermal expansion (CTE). In this context, this work aimed to improve the above properties without sacrificing the important benefit of this alloy being lightweight. Therefore, function grade composites (FGCs) were prepared based on the Mg10Li5Al alloy reinforced by yttrium (Y) and silica fume using the powder metallurgy technique. Then, the nanocomposite's microstructure, mechanical properties, artificial aging, wear resistance, and thermal expansion were examined. The results indicated that the precipitation (MgAlLi2), softening (AlLi2), and Mg24Y5 phases were formed in high-reinforced samples during high-energy milling. Furthermore, the addition of reinforcements accelerated the decomposition from the MgAlLi2 phase to the Al-Li phase (softening point). For the layer containing the highest reinforcement content, microhardness, strength, and Young's modulus improved up to 40, 22.8, and 41%, respectively, due to the combined effect of the high strength of silica fume and the dispersion strengthening Mg24Y5 phase. Meanwhile, the same sample exhibited a remarkable improvement in wear rate and the CTE value to about 43 and 16.5%, respectively, compared to the non-reinforced alloy.

Steady superlubricity achieved by epoxy resin composite coatings containing polydimethylsiloxane

Epoxy resin (EP) coatings have been widely applied in the field of surface protection engineering due to their high adhesion and good corrosion resistance, but the high friction and low wear resistance of pure EP coatings restrain their service life. Developing superior EP coatings with superlubricity and good antiwear performance is extensively desirable but remains to be a challenge yet. Here we for the first time report a superlubricious epoxy resin composite coating containing polydimethylsiloxane, PDMS (EP/PDMS) prepared by a facile solvent evaporation method. The PDMS was found to self-aggregate into nanoparticles in the epoxy resin matrix and leaded to the enhancement of tensile toughness of the epoxy resin coatings. The composite EP coatings containing PDMS performed steady superlubricity and high wear resistance when sliding against different bearing materials. Especially, an exceptionally and stable low friction coefficient of 0.007 was achieved by rotationally rubbing on the EP composite coating with a small content of 3.0 wt% against silicon nitride (Si3N4) ball in ambient air with a high relative humidity of 70 %, and the average wear rate of the EP/PDMS composite coating was as low as 2.76 × 10−7 mm3/N·m in spite of its low hardness.

A roller-bearing-based triboelectric nanosensor for freight train synergistic maintenance in smart transportation

Rail freight is a vital part of global economic development. The hunting instability of freight trains seriously affects safety. The lack of electrical pipelines between freight trains makes the energy of onboard monitoring equipment an urgent problem to be solved. In this paper, an energy self-consistent system (ESCS) based on a roller-bearing-based triboelectric nanosensor is proposed to detect the running status of freight trains while providing electric energy. The proposed ESCS consists of two modules: a roller-bearing-based triboelectric nanosensor (RB-TENS) module and a detection module. The RB-TENS module innovatively combines the advantages of low damping and wear resistance of roller bearings. Moreover, it incorporates energy harvesting and running status sensing for freight trains. While converting the train’s vibrational kinetic energy into electrical energy and storing it, the electrical signal containing the characteristics of the train’s running status is collected. The detection module includes a pre-processing module and a deep learning model based on LSTM. The characteristic electrical signal collected by RB-TENS is enhanced and extracted by the pre-processing module to generate training and testing sets. Using data set training and testing deep learning model, the freight train running status was recognized. On this basis, a dynamic model is established to study the effects of different axle loads, speeds, and pre-processing parameters on the vibration response, electrical performance, and deep learning model of the ESCS. Experiments show that the peak output power and energy density of RB-TENS reach 1.9 μW and 72 mW/m3. The results of the testing set show that the detection accuracy of ESCS reaches 96.6%, indicating that it can effectively detect the hunting instability of freight trains. This ESCS enables TENS to present a breakthrough in smart transportation and practical applications of the zero-energy Internet of Things.

Ceramic and Polymeric Composite Materials used in Reinforcing UHMWPE for Improved Mechanical and Tribological Properties in Orthopedic Applications

UHMWPE is a popular choice of biomaterial for joint replacements, particularly in hip, knee, and shoulder replacement procedures, notably as sliding material in between the load bearing surfaces due to its superior biocompatibility, tensile yield, impact strength, and high crystallinity. Even though it has good mechanical qualities, it has a relatively low wear resistance, which causes wear particles to shred and trigger immunological reactions and possibly osteolysis. This also has an impact on the implant’s lifetime. The wear issue can be solved using a variety of approaches, including thermal therapy and antioxidant infusion. The mechanical qualities suffer as a result of these methods’ efficacy in addressing tribological problems. One such way of reducing wear and oxidation rates while preserving mechanical characteristics is reinforcing the conventional UHMWPE with various composite materials. In this review the tensile and tribological properties of such ceramic and polymeric materials like zirconia, hydroxyapatite, carbon nanotube and graphene are evaluated. This review will investigate several ceramic and polymer-based fillers as an alternative to currently used methods such as improved radiation cross-linking and antioxidant treatment. CNT reinforced UHMWPE is still in the testing stage and is not yet on the market due to biocompatibility concerns. However, when compared to their competitors, their tribological properties are adequate but not exceptional. The best tensile properties are found in hydroxyapatite reinforced UHMWPE (but only at high concentrations such as 30wt%), followed by CNT. They do not have biocompatibility issues like CNT because of their structural similarity to natural bone. They also outperform CNT and ATZ composites in terms of tribological properties. As a result, they are best suited for reinforcement (with UHMWPE).

Atomic Cross-Talk at the Interface: Enhanced Lubricity and Wear and Corrosion Resistance in Sub 2 nm Hybrid Overcoats via Strengthened Interface Chemistry.

Friction, wear, and corrosion remain the major causes of premature failure of diverse systems including hard-disk drives (HDDs). To enhance the areal density of HDDs beyond 1 Tb/in2, the necessary low friction and high wear and corrosion resistance characteristics with sub 2 nm overcoats remain unachievable. Here we demonstrate that atom cross-talk not only manipulates the interface chemistry but also strengthens the tribological and corrosion properties of sub 2 nm overcoats. High-affinity (HA) atomically thin (∼0.4 nm) interlayers (ATIs, XHA), namely Ti, Si, and SiNx, are sandwiched between the hard-disk media and 1.5 nm thick carbon (C) overlayer to develop interface-enhanced sub 2 nm hybrid overcoats that consistently outperform a thicker conventional commercial overcoat (≥2.7 nm), with the C/SiNx bilayer overcoat bettering all other <2 nm thick overcoats. These hybrid overcoats can enable the development of futuristic 2-4 Tb/in2 areal density HDDs and can transform various moving-mechanical-system based technologies.

Improving high-temperature wear resistance of NiCr matrix self-lubricating composites by controlling oxidation and surface texturing

• NiCr matrix composites with WS 2 as lubricant suffer severer wear degradation at high temperatures • NiCr-WS 2 -Ti composite with heterostructure is prepared by spark plasma sintering. • The composite NiCr-WS 2 -Ti exhibits low friction coefficient and high wear resistance at elevated temperatures • Ti is preferentially oxidized, forming abundant TiO 2 protrusions and constructing in situ a special surface texture. • By controlling oxidation and surface texturing, a protective glaze layer formed at surface, leading to excellent tribological properties Self-lubricating composites (SLCs) are widely used in the fields of aerospace and marine, but the conventional NiCr matrix SLCs with sulfide as solid lubricant often suffer from low wear resistance at high temperatures. In view of its high affinity with oxygen and also the high oxidation rate, appropriate amount of nano Ti was added to NiCr-WS 2 composites prepared by spark plasma sintering (SPS) to adjust the oxidation behavior and surface texture. When exposed to high temperature, Ti was preferentially oxidized in comparison to Ni and Cr, resulting in abundant TiO 2 protrusions and microdimples on the surface, i.e. in situ surface texturing. Besides, TiO 2 was of high chemical activity and readily to react with other oxide debris during high temperature sliding process to form compounds of NiTiO 3 and CrTi 2 O 5 . The high chemical activity of oxide debris that was conducive to sintering, combining with the special surface texture that stores as many wear debris as possible, promoted the rapid formation of a protective glaze layer on the sliding surface. The NiCr-WS 2 -Ti composite exhibited low friction coefficient but high wear resistance at elevated temperatures. Especially at 800 °C, it presented a wear rate of as low as (2.1±0.3) × 10 −5 mm 3 N −1 m −1 , accounting for only 2.7% of that of NiCr-WS 2 composite.

A comparative study on microstructure, nanomechanical and corrosion behaviors of AlCoCuFeNi high entropy alloys fabricated by selective laser melting and laser metal deposition

• Hierarchically heterogeneous microstructures exist in both SLM- and LMD-processed specimens. • Core-shell FCC precipitates in LMD bear {110} texture at high surface energy and high strain energy. • Hot cracks occurred in both types of specimens due to the incompletely suppressed cu segregation. • A correlation mechanism between microstructure, nano-mechanics, and corrosion behavior was obtained. The present study investigated the microstructure, nanomechanics, and corrosion behavior of AlCoCuFeNi high entropy alloys fabricated by selective laser melting (SLM) and laser metal deposition (LMD). The microstructure of SLM-processed specimens was mainly composed of columnar-grained BCC matrix (∼90 µm in width) and Cu-rich twinned FCC phase. The columnar grains grew epitaxially along the building direction and exhibited a strong {001} texture. In comparison, a coarse columnar-grained BCC matrix (∼150 µm in width) with a stronger 〈001〉 texture, rod-like B2 precipitates, and large core-shell structured FCC phases were formed in the LMD-processed specimens due to the higher heat accumulation effect. Consequently, the LMD-processed specimens showed a lower hardness, wear resistance, and corrosion resistance, but higher creep resistance and reduced Young's modulus than the SLM-processed specimens. Hot cracks occurred in both types of specimens, which could not be completely suppressed due to Cu segregation.