新型填料对高摩复合材料摩擦磨损性能影响及机制

采用干法热压成型工艺制备高摩复合材料,研究了基体材料腰果壳油改性酚醛树脂(CPR)与丁晴橡胶(NR)的质量比和新型高性能填料(主要成分为石墨粉Al2O3、MoS2、Fe粉)含量对高摩复合材料摩擦磨损性能的影响规律。在摩擦磨损试验机上测试了高摩复合材料的摩擦磨损性能,利用激光共聚焦显微镜、扫描电镜对摩擦表面形貌、磨屑进行观察和分析,借助EDS测定摩擦表面成分的变化。结果表明,随着CPR与NR质量比的增加,高摩复合材料的耐热性能、结合性能大幅提高,且具有较好的摩擦磨损性能。当高性能填料含量较低时,磨损表面出现大量连续的真实接触面,磨损机制为磨粒磨损和黏着磨损;当高性能填料含量较高时,真实接触面积减少,磨损表面剥落严重,并出现较多的裂纹,其主要磨损形式转变为磨粒磨损和疲劳磨损。随着高性能填料含量的增加,摩擦表面的元素从均匀分布逐渐转变为局部富集,磨粒的尺寸逐渐变大。     

三嗪树枝状大分子的合成与表征

以二乙胺、三聚氯氰、哌嗪为单体,通过收敛法合成了两种系列的端氯基和端胺基树突,以及3代的内核为哌嗪、端基分别含8个和16个乙基的三嗪树枝状大分子,对产物进行了红外光谱（IR）、核磁共振（1H-NMR、13C-NMR）、质谱（MS）表征。该方法所需原料价廉易得,反应条件温和,无需繁杂的官能团保护与脱保护,无需色谱法分离,...     

Structural characterization of quinoxaline homopolymers and quinoxaline/ether sulfone copolymers by matrix-assisted laser desorption ionization mass spectrometry

Polyphenylquinoxalines (PPQs) are prepared from self-polymerizable quinoxaline monomers that carry fluorine, hydroxyaryl (ArOH), and phenyl substituents. In basic media, these monomers self-polymerize via a series of nucleophilic aromatic substitution reactions (SNAr), in which aromatic enolates (ArO- nucleophiles) attack the electrophilic carbons bearing F leaving groups to effect fluoride displacement. Polyphenylquinoxaline/polyether-sulfone (PPQ/PES) copolymers are synthesized similarly by combining self-polymerizable quinoxaline monomers with a 1:1 molar mixture of 4,4'-dichlorodiphenyl sulfone and bisphenol A. The MALDI mass spectra of the polymers reveal that the major products up to approximately 15,000 Da molecular mass are homo- or copolymeric macrocycles. Linear byproducts are also observed, arising from nucleophilic ring opening of already formed macrocycles. Oligomers containing at least one PPQ unit readily protonate upon MALDI, whereas PES homopolymers require alkali metal ion addition to become detectable. Molecular orbital calculations point out that the nucleophilic and electrophilic reactivities of the PPQ monomer and the PPQ growing chains generated during propagation are comparable, allowing for continued condensations via SN-Ar, until cyclization terminates this process. The calculations also predict a significantly lower electrophilic reactivity for carbons substituted by chlorine instead of fluorine, justifying the discrimination against incorporation of PES units observed for the copolymers. The computationally optimized structures of PPQ and PPQ/PES macrocycles show a diverse array of cavity sizes and geometries which depend on the size of the macrocycle, the sequence of the repeat units, and the position of the substituents in the quinoxaline ring; quinoxaline pendants (phenyl groups) are found to favor helical arrangements in the prepared macrocycles.     

Effect of friction time on flash shape and axial shortening of linear friction welded 45 steel

The influence of friction time on the flash (upset metal) shape and axial shortening during linear friction welding of 45 steel under an appropriate welding condition was examined. It was found that a sound weld with the fine structures could be formed as the friction time not less than 3 s. The axial shortening was exponentially increased with increasing the friction time. The periodical ridges presented in the flash were formed through the reciprocating motion and expelling of the plasticized materials. The flash in the friction direction presents an undulating-ribbon structure, while that in the vertical direction looks like a little curly swirl. The curved ridges were caused by the non-uniform extrusion rates of materials in the middle and edge resulting from the non-uniform temperatures.     

Hierarchical adaptive nanostructured PVD coatings for extreme tribological applications: the quest for nonequilibrium states and emergent behavior

Adaptive wear-resistant coatings produced by physical vapor deposition (PVD) are a relatively new generation of coatings which are attracting attention in the development of nanostructured materials for extreme tribological applications. An excellent example of such extreme operating conditions is high performance machining of hard-to-cut materials. The adaptive characteristics of such coatings develop fully during interaction with the severe environment. Modern adaptive coatings could be regarded as hierarchical surface-engineered nanostructural materials. They exhibit dynamic hierarchy on two major structural scales: (a) nanoscale surface layers of protective tribofilms generated during friction and (b) an underlying nano/microscaled layer. The tribofilms are responsible for some critical nanoscale effects that strongly impact the wear resistance of adaptive coatings. A new direction in nanomaterial research is discussed: compositional and microstructural optimization of the dynamically regenerating nanoscaled tribofilms on the surface of the adaptive coatings during friction. In this review we demonstrate the correlation between the microstructure, physical, chemical and micromechanical properties of hard coatings in their dynamic interaction (adaptation) with environment and the involvement of complex natural processes associated with self-organization during friction. Major physical, chemical and mechanical characteristics of the adaptive coating, which play a significant role in its operating properties, such as enhanced mass transfer, and the ability of the layer to provide dissipation and accumulation of frictional energy during operation are presented as well. Strategies for adaptive nanostructural coating design that enhance beneficial natural processes are outlined. The coatings exhibit emergent behavior during operation when their improved features work as a whole. In this way, as higher-ordered systems, they achieve multifunctionality and high wear resistance under extreme tribological conditions.     

Identification, Composition, and Asymmetric Formation Mechanism of Glycidyl Methacrylate/Butyl Methacrylate Copolymers up to 7000 Da from Electrospray Ionization Ultrahigh-Resolution Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

Glycidyl methacrylate (GMA) and butyl methacrylate (BMA) have the same nominal mass (142 Da) but differ in exact mass by 0.036 Da (CH(4) vs O). Therefore, copolymers formed from the two isobaric monomers exhibit a characteristic isobaric distribution due to different monomer compositions. Here, we show that electrospray ionization FT-ICR mass spectrometry at 9.4 T resolves the isobaric components of copolymers as large as 7000 Da with a resolving power (m/Δm(50%)) of ～500?000 in a gel permeation chromatography fractionated polymer sample. That resolution provides for complete and unequivocal component analysis of such copolymers of the size used for high solid content automobile coatings. All five possible copolymer products predicted by the polymerization mechanism are resolved and identified in the mass spectrum. Two of those polymer series (each with saturated end group) were previously unresolved by mass spectrometry because they differ in mass from the two other unsaturated products by only 0.0089 Da. Finally, analysis of the asymmetrical isobaric distribution for the copolymer n-mers, (GMA)(m)(BMA)(n)(-)(m), 0≤ m ≤ n, in which species with adjacent values of m differ from each other in mass by 36 mDa (i.e., the mass difference, CH(4) vs O, between GMA and BMA) proves that GMA is less reactive than BMA in the polymerization process.     

Hafnium-containing nanocomposites

New types of hafnium-containing nanocomposites are prepared by combining polymer synthesis and controlled thermolysis. This approach involves the preparation and subsequent thermolysis of hafnium-containing polymers or concurrent solid-state polymerization of hafnium-containing monomers and thermal decomposition of the forming metal-containing polymer at different temperatures. The composition and structure of the synthesized hafnium-containing precursors and thermolysis products are determined by elemental analysis, IR spectroscopy, mass spectrometry, optical microscopy, and x-ray diffraction. Thermodynamic analysis is used to assess the equilibrium composition of the Hf-C-H-O system and establish the conditions under which HfC and HfO₂ are formed.     

CPR/NR和高性能填料对复合摩擦材料力学性能的影响

通过干法热压成型工艺制备性能优异的复合摩擦材料,研究了高性能填料以及改性酚醛树脂与丁腈橡胶质量比(CPR/NR)对复合摩擦材料性能的影响规律。对材料的摩擦磨损性能与力学性能进行了测试,借助热分析仪测试其耐热性能,并利用激光共聚焦显微镜、扫描电镜对表面形貌进行了观察和分析。结果表明,复合摩擦材料的密度、压缩强度、压缩模量、硬度随橡胶含量的减少而增加,冲击强度则呈相反的趋势。橡胶含量的减少,树脂比例的增加,使复合摩擦材料的耐热性得到提高,促进了第二接触面的形成,使摩擦系数与磨损率降低。高性能填料含量较低时,材料表面形成大且连续的第二接触面,第二接触面使摩擦系数、比磨损率降低,复合摩擦材料的主要磨损形式为粘着磨损与磨粒磨损;填料含量的增加会阻碍第二接触面的形成,使材料摩擦系数和比磨损率逐渐增大,材料的磨损形式由粘着磨损、磨粒磨损转变为磨粒磨损和疲劳磨损。     

Hierarchical adaptive nanostructured PVD coatings for extreme tribological applications: the quest for nonequilibrium states and emergent behavior

Abstract

Adaptive wear-resistant coatings produced by physical vapor deposition (PVD) are a relatively new generation of coatings which are attracting attention in the development of nanostructured materials for extreme tribological applications. An excellent example of such extreme operating conditions is high performance machining of hard-to-cut materials. The adaptive characteristics of such coatings develop fully during interaction with the severe environment. Modern adaptive coatings could be regarded as hierarchical surface-engineered nanostructural materials. They exhibit dynamic hierarchy on two major structural scales: (a) nanoscale surface layers of protective tribofilms generated during friction and (b) an underlying nano/microscaled layer. The tribofilms are responsible for some critical nanoscale effects that strongly impact the wear resistance of adaptive coatings. A new direction in nanomaterial research is discussed: compositional and microstructural optimization of the dynamically regenerating nanoscaled tribofilms on the surface of the adaptive coatings during friction. In this review we demonstrate the correlation between the microstructure, physical, chemical and micromechanical properties of hard coatings in their dynamic interaction (adaptation) with environment and the involvement of complex natural processes associated with self-organization during friction. Major physical, chemical and mechanical characteristics of the adaptive coating, which play a significant role in its operating properties, such as enhanced mass transfer, and the ability of the layer to provide dissipation and accumulation of frictional energy during operation are presented as well. Strategies for adaptive nanostructural coating design that enhance beneficial natural processes are outlined. The coatings exhibit emergent behavior during operation when their improved features work as a whole. In this way, as higher-ordered systems, they achieve multifunctionality and high wear resistance under extreme tribological conditions.     

孔隙率对碳纤维增强纸基摩擦材料摩擦磨损性能的影响

碳纤维增强纸基摩擦材料是应用于汽车自动变速器中的一种新型湿式摩擦材料. 在固定原材料配比和含量的基础上, 通过改变摩擦材料厚度, 制备出几种孔隙率不同的碳纤维增强纸基摩擦材料. 采用液体渗透法测试摩擦材料的孔隙率. 利用扫描电镜观察试样形貌. 通过惯量试验机研究孔隙率对碳纤维增强纸基摩擦材料湿态摩擦磨损性能的影响. 试验结果表明: 短切碳纤维在树脂基体中均匀分散, 相互桥接, 形成了大小不一的贯穿性孔隙; 随着孔隙率的增大, 摩擦力矩曲线趋于平稳; 动摩擦系数升高, 静摩擦系数降低, 磨损率增大.     

Microstructure and mechanical properties of alumina-6061 aluminum alloy joined by friction welding

The study of the interface of ceramic/metal alloy friction welded components is essential for understanding of the quality of bonding between two dissimilar materials. In the present study, optical and electron microscopy as well as four-point bending strength and microhardness measurements were used to evaluate the quality of bonding of alumina and 6061 aluminum alloy joints produced by friction welding. The joints were also examined with EDX (energy dispersive X-ray) in order to determine the phases formed during welding. The bonded alumina-6061 aluminum samples were produced by varying the rotational speed but keeping constant the friction pressure and friction time. The experimental results showed that the effect of rotation speed and degree of deformation appears to be high on the 6061 Al alloy than on the alumina part. It is discovered that the weld interface formed included three different regions: unaffected zone (UZ), deformed zone (DZ), as well as transformed and recrystallized fully deformed zone (FPDZ). Therefore, when rotational speed increases, the thickness of full plastic deformed zone (FPDZ) at the interface increases as a result of more mass discarded from the welding interface. It was also observed that rotational speed of 2500 rpm can produce a very good joint and microhardness with good microstructure as compared to the other experimental rotational speeds.     

Contact with friction in multi‐material arbitrary Lagrangian‐Eulerian formulations using X‐FEM

A contact method with friction for the multi‐dimensional Lagrangian step in multi‐material arbitrary Lagrangian–Eulerian (ALE) formulations is presented. In our previous research, the extended finite element method (X‐FEM) was used to create independent fields (i.e. velocity, strain rate, force, mass, etc.) for each material in the problem to model contact without friction. The research presented here includes the extension to friction and improvements to the accuracy and robustness of our previous study. The accelerations of the multi‐material nodes are obtained by coupling the material force and mass fields as a function of the prescribed contact; similarly, the velocities of the multi‐material nodes are recalculated using the conservation of momentum when the prescribed contact requires it. The coupling procedures impose the same nodal velocity on the coupled materials in the direction normal to their interface during the time step update. As a result, the overlap of materials is prevented and unwanted separation does not occur. Three different types of contacts are treated: perfectly bonded, frictionless slip, and slip with friction. Example impact problems are solved and the numerical solutions are presented. Copyright © 2008 John Wiley & Sons, Ltd.     

碳化硅/碳化钨硬面密封摩擦副的摩擦磨损性能和机理研究

实验研究了干摩擦和水润滑条件下, 常压固相烧结碳化硅陶瓷(SSiC)及常压液相烧结碳化硅陶瓷(LPSiC)分别与碳化钨(WC)组成的硬面配对摩擦副的滑动摩擦磨损性能。在干摩擦条件下, 与LPSiC/WC摩擦副相比, SSiC陶瓷由于具有更大的晶粒尺寸和硬度, 导致SSiC/WC摩擦副具有更大的摩擦系数和更小的磨损量。磨损区域的SEM形貌结合面扫描分析、微区XRD分析结果表明: 微犁沟和微断裂导致SiC陶瓷的磨损, 疲劳损伤导致WC材料的磨损, 而摩擦过程产生的摩擦热导致磨出的WC颗粒氧化成无定型WO₃。在水润滑条件下, 与SSiC/WC摩擦副相比, LPSiC/WC摩擦副具有更大的摩擦系数和更低的磨损率。在干摩擦和水润滑条件下, 与SiC陶瓷作为动摩擦副配对相比, SiC陶瓷作为固定摩擦副的摩擦配对具有更小的摩擦系数和质量损失。     

Synthesis and characterization of metal ion-imprinted polymers

In this study, ion-imprinted polymeric materials from an aqueous solution were prepared to remove metal ions \((\hbox {M}^{2+})\) like \(\hbox {Ni}^{2+}\), \(\hbox {Co}^{2+}\), etc. To prepare ion-imprinted polymers (IIPs), acrylic acid derivatives (XA) like acrylamide (AAm), methacrylic acid and itaconic acid were chosen as monomers. Metal ions formed binary chelate complexes with the help of 8-hydroxyquinoline (8-HQ). The solution containing functional monomers and the binary complex were polymerized with the help of various cross-linkers [ethylene glycol dimethylacrylate (EGDMA) or trimethylpropane trimethacrylate (TMPTMA)] and the target ion was removed from this polymer through an applicable method to produce IIPs. Furthermore, the control polymers (CPs) were synthesized through the same method without using metal ion. Characterization of the polymeric materials was investigated through spectroscopic (FTIR/ATR), thermal (TGA, DSC) and surface (SEM and XRD) analyses. Functional monomers, cross-linkers and the target ion’s species were changed during preparation of IIPs to observe their effect on imprinting of the target ion. Adsorption of the target ion to the prepared IIPs and the factors affecting the adsorption like concentration, pH, temperature, mass, etc. were studied.     

Synthesis of Photopolymerizable Hydrophilic Macromers and Evaluation of Their Applicability as Reactive Resin Components for the Fabrication of Three‐Dimensionally Structured Hydrogel Matrices by 2‐Photon‐Polymerization

Two‐photon polymerization (2‐PP) is a promising new photolithographic technique to fabricate three‐dimensional (3D), micro‐ and nano‐structured tissue engineering scaffolds from photopolymerizable monomers. Although various photo resins are known for the use in 2‐PP, there is currently a need for photo‐curable monomers processable by 2‐PP to generate biocompatible 3D‐structured hydrogel materials for soft or cartilage tissue regeneration. In the present work hydrophilic methacrylate monomers and macromers based on synthetic poly(glycerine) and poly(ethylene glycol) urethanes as well as on the biopolymers dextran and hyaluronan is prepared. The photopolymerization behavior of these substances are investigated and formed hydrogel networks are studied with regard to their mechanical properties, cytocompatibility, and hydrolytic degradation. Based on these examinations simple 3D model structures are fabricated from these photo‐curable monomers and macromers by 2‐PP. It is shown that both the synthetic monomers and the dextran methacrylate macromer are efficient 2‐PP starting materials whereas the hyaluronan methacrylate can be used for 2‐PP only in combination with suitable water‐soluble co‐monomers. No cytotoxic effects are found in preliminary chondrocyte cultivation experiments on 2‐PP‐fabricated scaffolds but initial cell adhesion on the hydrophilic scaffold surfaces is rather low and has to be further improved to apply these structures in tissue engineering.     

Characterization of light-cured dimethacrylate resins modified with silsesquioxanes

Methacrylate-functionalized silsesquioxanes (SSQO) were synthesized by the hydrolytic condensation of 3-(methacryloxypropyl) trimethoxysilane (MPTMS) using dimethacrylate monomers as reactive solvent. Resins containing about 40 wt% SSQO displayed a modest increase in viscosity compared with the unmodified methacrylate monomer. This is attributed to a dilution of the reacting medium, which discourages bimolecular reactions that lead to the generation of high-molar mass oligomers and, consequently, prevents undesired increases of viscosity. Substitution of monomer with SSQO reduced the volumetric shrinkage during photopolymerization. The amount of leachable monomer detected in formulations containing SSQO was markedly reduced. This indicates that the unreacted monomer exists mainly as pendant chains instead of free leachable monomer. The presence of different proportions of SSQO in the methacrylate monomer resulted in no apparent change in the flexural modulus and in a modest decrease in the compressive yield stress of the polymerized materials. From results presented in this research, it emerges that methacrylate monomers modified with SSQO are attractive for applications that require reduced volumetric shrinkage and long storage periods, such as light-cured dental restorative composites.     

粉煤灰增强树脂基摩擦材料磨屑形貌及成分分析

通过干法热压工艺制备了粉煤灰增强树脂基摩擦材料,利用D-MS型定速式摩擦试验机测其在不同温度下的摩擦磨损性能,并收集磨屑。借助扫描电子显微镜观察、分析样品摩擦后的表面和磨屑形貌,研究了摩擦材料磨损的内在机制,并借助X射线衍射仪、X射线能谱仪、红外光谱仪进行综合表征。结果表明,添加粉煤灰的树脂基摩擦材料摩擦表面形成连续、稳定的摩擦膜,能够有效改善树脂基摩擦材料的摩擦磨损性能。对磨屑的分析实验证明摩擦膜的产生与粉煤灰中SiO2和Al2O3有关。     

Qualitative identification of fumaric Acid and itaconic Acid in emulsion polymers

A pyrolysis gas chromatography (Py-GC) technique has been used for the qualitative analysis of fumaric acid and itaconic acid as low-level monomers polymerized with other major monomers in emulsion polymers. In order for fumaric acid and itaconic acid to be detected through pyrolysis, the acids are derivatized with primary amines such as methylamine and ethylamine to form a cyclic imide. The detection of derivatized fumaric acid and itaconic acid is accomplished by atomic emission detection (AED). The structures of the derivatization-pyrolysis products have been elucidated by mass spectrometry.     

不同制动速度下C/C复合材料摩擦面研究

采用MM-1000型摩擦磨损试验机测试了粗糙层基体炭C/C复合材料试样在不同制动速度下的摩擦磨损性能, 借助微区拉曼光谱和扫描电镜研究了试样摩擦面的结构与形貌。结果表明粗糙层基体炭C/C复合材料具有优异的摩擦速度特性。试样的摩擦系数和试验后摩擦面上碳原子的有序度无直接对应关系, 制动速度对摩擦系数的影响应归因于制动速度对摩擦面温升和摩擦膜厚度及完整性的影响。5m/s的低制动速度下, 试样因吸附水气摩擦系数持续低值(0.15), 摩擦面上无连续摩擦膜产生; 10m/s的制动速度下水气被解吸附, 摩擦面出现多层厚膜, 摩擦系数达到峰值(0.5), 此后, 随制动速度增加, 摩擦膜减薄, 材料磨损量呈下降趋势; 当制动速度增加到25m/s及以上, 摩擦面的温升导致氧化质量损失和线磨损增加, 摩擦系数也稍有衰减(0.3)。      

PTFE微粉/CF改性PEEK复合材料的摩擦磨损性能

为解决核电水循环系统中鼓型旋转滤网驱动装置的耐腐蚀问题,本文研究了碳纤维和聚四氟乙烯微粉改性的聚醚醚酮复合材料在干摩擦、水润滑和油润滑条件下的摩擦磨损性能.通过机械共混、高温模压的方法,制备了不同质量分数的聚四氟乙烯(PTFE)微粉/碳纤维(CF)/二硫化钼(MoS_2)/聚醚醚酮(PEEK)复合材料.采用拉伸试验机和塑料洛氏硬度计测试其力学性能,采用摩擦磨损试验机测试了复合材料在干摩擦、水润滑和油润滑条件下的摩擦磨损性能,采用扫描电子显微镜对其摩擦表面形貌进行分析.结果表明:复合材料在水润滑和油润滑时摩擦系数及磨痕宽度均较小,但水润滑时摩擦系数波动幅度较大且磨痕宽度略高;复合材料在干摩擦条件下的磨损机制以磨粒磨损为主,伴有疲劳磨损,油润滑时摩擦面可形成连续的润滑膜而保持光滑,水润滑时水流冲刷破坏了摩擦面上固体润滑膜的稳定性;CF质量分数增加时,复合材料的洛氏硬度和压缩强度递增,压缩强度达到164 MPa,PTFE微粉质量分数增加时,复合材料的洛氏硬度和压缩强度递减;CF质量分数增加时,复合材料的干摩擦系数及磨痕宽度下降,PTFE微粉质量分数增加时,复合材料的干摩擦系数下降,达到0.17.