Tribological and corrosion performance of epoxy resin composite coatings reinforced with graphene oxide and fly ash cenospheres

In this work, a novel graphene oxide (GO)-fly ash cenospheres (FACs) hybrid fillers was introduced to improve the wear and corrosive resistance of epoxy resin (ER) composite coatings. The tribological behavior and the corrosion performance of three kinds of coatings (pure ER, GO/ER and GO-FACs/ER coatings) were studied and the reinforced mechanisms of coatings filled by different fillers were analyzed. The friction coefficient and wear rate of the ER coatings were decreased with the addition of GO-FACs hybrids. The scanning electron microscope images showed that the dispersibility and compatibility of GO-FACs hybrids were effectively improved compared with that of GO sheet. The water contact angle examination indicated that the hydrophobicity of the GO-FACs/ER coatings increased. The electrochemical impedance spectroscopy (EIS) results demonstrated that the GO-FACs/ER coatings have better anticorrosion performance compared with the pure ER coatings and the GO/ER coatings. The hydrophobic surface and the well dispersed fillers constitute the dual barrier to resist the corrosion medium.     

Hybrid polymer matrix composite (UHMWPE-HPMC) as solid particle erosion resistant coating for sharp pipe elbows using numerical simulation and experimental analysis

A hybrid polymer matrix composite coating, resistant to solid particle erosion inside sharp elbows, consisting interlocking chains of molecules with the ability to deflect the surface impact stress and to uniformly distribute stresses along the hard-ceramic reinforcement mixture surface was developed. Formulated mixture of ceramic reinforcement particles mixtures (alumina, tungsten carbide, and silicon carbide) with polymer coupling agents; to increase adhesion to the metal surface, led to 600–700 HVN in ternary and 500–550 HVN in binary mixtures. This behavior coincides with high shear strength of 70–76 MPa, Young's and shear modulus of 8.86 and 13.4 GPa in ternary 15%Al₂O₃-5%WC-10%SiC, respectively. The low erosion weight loss of 0.1% and small coefficient of friction near 0.18 indicates the significant wear resistance of the ternary sample. The electron microscopic micrographs determined the dense smooth coating surfaces with adhesive interfaces with the substrate.     

Sodium citrate-assisted synthesis of nano-manganese oxide on carbon fiber for enhancing the mechanical and frictional performances of carbon fiber-reinforced resin matrix composites

Aiming to enhance the carbon fiber (CF)/resin interfacial adhesion, this report describes the novel application of sodium citrate (SC) as an auxiliary reducing agent and surface regulator to control the morphology of nano-manganese dioxide (MnO₂) on the CF surface. The composites were fabricated by means of controlling the molar concentration ratio of SC to Mn source (0:1, 1:3, 1:2, and 1:1) in hydrothermal synthesis. The results reveal that MnO₂ nanosheets on the CF surface become denser as the concentration of SC is 1/3 of Mn source, which makes advance to the surface roughness and surface energy of CF. Simultaneously, the tensile strength of as-prepared composite is increased by 52.8%. The homologous friction coefficient tends to be high and stable and the wear volume is significantly reduced by 63.8 and 26.5% under the applied loads of 3 and 5 N in contrast with the original composites prepared without SC. As a result, it can be inferred that SC plays a crucial role in enhancing the interfacial bonding strength between the CF and matrix, providing insights into the interface control of CF-reinforced resin matrix composites.     

An investigation on wear behavior of UHMWPE/carbide composites at elevated temperatures

Ultra-high molecular weight polyethylene (UHMWPE) is extensively used in frictional applications due to its advanced wear resistance. This advanced polymer is reinforced with hard particulate fillers for further developments against wear conditions. Since elevated temperatures prevail in the service conditions, wear behavior of UHMWPE composites is an important issue for the engineering applications. In the present work, UHMWPE-based composites including silicon carbide (SiC) fillers were fabricated in a compression molding chamber. In the specimen preparation stage, molding pressure, filler amount, and filler particle size were varied to investigate the influence of these variables. Upon deciding the optimum parameters from the wear tests conducted at room temperature, the wear experiments were repeated for the optimum specimen at elevated temperatures, such as 40 and 60°C. According to the results, the wear behavior of the SiC/UHMWPE composites is heavily changed by the effect of elevated temperature. Adhesive effect is pronounced at elevated temperatures while the wear characteristics possess the abrasive effect in the sliding path. In addition, the composites exhibit an accelerated material loss as temperature increases during the frictional system.     

Preparation and tribological behavior of polytetrafluoroethylene/metal mesh composites with sandwich structure

Polytetrafluoroethylene (PTFE) owns an excellent self-lubricating performance, but its wear rate is very high due to the large-scale spalling of the matrix in the friction. In this paper, A new kind of PTFE composites with sandwich structure was prepared by layer-press technology, whose middle layer is filled with metal mesh. The influence of the mesh structure and mesh density of middle metal layer on tribological properties of composites were researched in detail. The results revealled that the metal mesh located in the composites can efficiently prevent the large-scale spalling of PTFE, which induces the sample of PTFE/500# plain woven dutch metal mesh (PTFE-500#PWD) to have a lower wear rate (9 × 10⁻⁵ mm³/Nm) and COF (0.106) under the fixed experimental condition. The prepared PTFE/metal mesh composites reveal excellent anti-friction and anti-wear performance, which can be used to fabricate a new kind of self-lubricating materials.     

Hydrogen bonding induced enhancement for constructing anisotropic sugarcane composite hydrogels

Anisotropic hydrogels are appealing with their merits of similar biochemical and structural properties to the biological tissues. However, the mechanical properties of current anisotropic hydrogels need to be further improved. Herein, three kinds of novel anisotropic poly(2-hydroxyethyl methacrylate) (pHEMA), poly(acrylamide) (pAM), and poly(acrylamide-co-acrylic acid) (p[AM-co-AA]) sugarcane composite hydrogels were prepared successfully by filling the hydrogel monomer precursor into porous aligned sugarcane nanofibers network and then performing subsequent free radical polymerization. The hydrogel matrix and sugarcane nanofibers network were combined closely together through hydrogen bonding interaction. The anisotropic sugarcane composite hydrogels exhibit good flexibility and elastic recovery properties upon encountering mechanical crimping and twisting. In typical case, the as-prepared pHEMA sugarcane composite hydrogel can exhibit high anisotropic tensile strength of 2.37 and 0.54 MPa, while differential tear strength of 0.36 and 0.78 N/mm, along the parallel and vertical nanofibers directions. Finally, anisotropic lubrication behaviors were found and investigated systematically for those three kinds of sugarcane composite hydrogels when water was used as lubricant. Our current work proposes a simple and universal strategy for developing bioinspired anisotropic functional composite matters such as artificial skin, flexible sensor, and cartilage lubrication materials.     

Effect of nano fillers on the properties of polytetrafluoroethylene composites: Experimental and theoretical simulations

Polytetrafluoroethylene (PTFE) has excellent corrosion resistance and a low coefficient of friction; however, its high wear rate and low hardness severely limit its use. In the work, nano particles were used as fillers for PTFE. The composites were prepared by the homogeneous mixing of PTFE and other fillers and sintered at high temperatures. The work aimed to investigate the effect of various nano fillers (nanocarbon powders, graphene, fullerene, nano graphite powders, and nano copper powders) on the mechanical, thermal, and frictional properties of composites. The results of the experiments showed that the addition of graphene could improve the stress and strain values of the composites, and all the nano fillers could improve the thermal conductivity of the PTFE composites. The friction experiments showed that fullerenes could significantly improve the wear resistance of PTFE composites. In the theoretical simulation, the thermal conductivity of PTFE composites was predicted using ANSYS software, with the changes in the temperature and friction force in the friction process. The theoretical simulation results matched with the experimental values, which proved the accuracy of the theoretical simulations.     

纳米金刚石的应用

纳米金刚石不仅具有金刚石所固有优异特性，而且还具有纳米材料所拥有的奇异性能。正是这些综合技术特性，使得它在传统的和新的技术领域中得到应用，并初见成效，本文从超精抛光、润滑、复合镀、磁性录音系统和医疗等方面的应用做了扼要的叙述，指出，纳米金刚石颗粒具有球形和准球形的特点，使得摩擦表面形成滚珠轴承效应，而表现出良好的润滑性，从而避免于摩现象的发生，而对一些主要因接触疲劳或高温磨损而失效的工件，纳米金刚石金属的复合涂层，则具有明显的优越性。     

Effect of sintering parameters on warm compacted iron-based material

1　INTRODUCTIONItiswellknownthatincreasingdensityisthebestwaytoincreasetheperformanceofpowdermet allurgy(P/M ) parts.ConventionalP/Mprocessingcanproduceiron basedpartswithdensitylessthan 7.1g/cm3(arelativedensityof 90 %approximately) .Theirmechanicalpropertiesaresubstantiallylessthanthoseoftheirfulldensitycounterpart .TherearemanymethodsthatcanproduceP/M partswithrela tivelyhighdensitysuchaswarmcompaction ,hightemperaturesintering ,doublepress/doublesinteringandforging .Warmcompactioni…     

提高油气润滑使用效果的措施

介绍了油气润滑的组成、原理及优缺点，并着重阐述了油气润滑使用中存在的问题和对策。