Real-time SEM/FIB studies of whisker growth and surface modification

We report on real-time measurements that enable us to watch the morphology of whiskers and hillocks forming in real-time and provide insight into the mechanisms controlling their growth and initiation. These measurements show that whiskers appear to grow out of a single grain on the surface with little lateral growth. To understand why whiskers initiate at specific sites, we modified the surface using the focused ion beam to remove the oxide in selected areas. Whiskers did not grow out of these uncovered areas, indicating that the underlying grain structure is important to whisker growth and it is not sufficient to just remove the oxide barrier. In comparison with whiskers, we found that hillock formation is accompanied by a large amount of grain growth and often by grain rotation at the surface.     

碳纤维表面镀铜SEM表征及XPS分析

采用电镀法制备了镀铜短碳纤维,借助扫描电子显微镜(SEM)对镀层微观形貌以及镀层厚度进行了微观表征,并利用X射线光电子能谱(XPS)分析技术对镀层的化学成分和镀层中主要元素化合价态进行了分析?结果表明:经过预处理的碳纤维表面变得粗糙,有很多亲水性含氧官能团;电镀电压2 V,电镀时间20 min,电镀温度30 ℃时,可获厚度约1.2 μm?短碳纤维端头被镀层紧紧包裹的均匀电镀层;镀层中间大部分铜以单质形式存在,表面镀铜层被氧化成氧化铜,镀层仿形生成,与碳纤维形成一个紧密的镶嵌体系?     

Effect of surface state of carbon fiber electrode on copper electroplating from sulfate solutions

The effect of the fiber surface state of a carbon fiber fabric on the parameters of copper electro-plating from a sulfate solution (the copper current efficiency, the electroplating rate, and the deposit distribution in the depth of electrode) is studied. The surface state of fibers was changed by preliminarily polarizing the carbon fiber fabric in electrolyte solutions. The change in the specific conductivity and weight of the carbon fiber fabric, as well as the surface state of oxides and the morphology of the copper deposit, depending on the conditions of electrode polarization was studied.     

铜纤维多孔表面孔结构对池沸腾换热性能的影响

本文分别以30 μm、50 μm、100 μm和160 μm四种直径的紫铜纤维毡与紫铜基板构成的多孔材料为研究对象,针对紫铜纤维毡孔隙度分别为90%、80%和75%下,四种直径的纤维多孔材料池沸腾换热性能进行了检测,并与紫铜基板池沸腾换热性能进行对比。研究结果表明：紫铜纤维多孔材料具有良好的强化池沸腾换热性能,当过热度ΔT <20oC时,紫铜纤维多孔材料换热性能是紫铜基板换热性能的2~5倍;当紫铜纤维毡孔隙度为90%时,多孔材料的换热性能随着纤维直径的减小而增强;当纤维直径为160μm时,多孔材料的换热性能随着纤维毡孔隙度的减小而增强。紫铜纤维多孔材料池沸腾换热性能受多孔材料内部汽化核心数目、汽泡溢出阻力和毛细吸力等多种因素的影响。因此,在不同的工作条件下,纤维多孔材料具有不同的最佳孔结构参数。     

PAN基碳纤维长周期结构的温度依赖性

采用SAXS和HRTEM方法从倒易空间和实空间分别研究了PAN纤维碳化及石墨化过程中长周期结构及其变化。通过HRTEM测试发现碳纤维中存在由石墨微晶的有序堆砌结构,无序堆砌结构及过渡区形成的层状长周期结构,同时碳纤维的SAXS赤道方向散射曲线中出现肩峰,说明这种长周期结构沿纤维径向堆砌。通过SAXS研究发现,在PAN纤维碳化过程中长周期结构从700℃时开始出现且其尺寸随热处理温度的变化呈先增大后减小的趋势,转折温度区域约为1350℃左右。通过一维相关函数分析,计算了长周期结构中石墨微晶有序堆砌结构尺寸(Lo)、无序堆砌结构尺寸(Ld)、过渡区尺寸(Ltr)随热处理温度的变化:1350℃之前,Lo、Ld趋于增大,而Ltr趋于减小;1350℃之后3个参数均呈减小的趋势。     

相控阵超声检测技术在碳纤维结构分层缺陷检测中的试验

以碳纤维层压结构中容易产生的分层缺陷为研究对象,采用相控阵超声检测技术进行CIVA仿真和检测试验。通过声场及缺陷的建模和CIVA仿真检测试验,得出了碳纤维层压结构分层缺陷的理想检测参数。设计制作了模拟分层试验件,并进行实际检测试验,结果表明相控阵超声技术可以有效地检测该类缺陷。     

Toughening of carbon fiber/pitch-based carbon matrix composites by microspace control

A relation between the pore structure and the fracture resistance is examined on carbon fiber/pitch-based carbon matrix composites since pores are considered an important microspace component affecting the fracture behavior in the composites. A part of the pores may lie on a fiber surface so that the bonding force at the fiber/matrix interface is varied depending on the size and the spatial distributions of the pores. The change in the bonding force distribution brings a large-scale fiber pullout process into the composites. Therefore, the fracture resistance can be improved by controlling the microspace of the composites.     

Effect of carbon fiber on microstructure evolution and surface properties of FeCoCrNiCu high-entropy alloy coatings

FeCoCrNiCu and C_f/FeCoCrNiCu high-entropy alloy coatings are prepared by laser cladding to study the effects of carbon fiber on the microstructure and surface properties of the FeCoCrNiCu alloy. It is found that the addition of carbon fiber has little effect on the phase structure of the FeCoCrNiCu alloy coating. However, an interesting finding is that the addition of carbon fiber could decrease the segregation of Cu-element along the grain boundaries in the FeCoCrNiCu coating. In addition, the addition of carbon fiber can significantly improve the corrosion resistance of the FeCoCrNiCu alloy coating. It can also reduce the intergranular corrosion in the coating. Moreover, the addition of carbon fiber has positive effects on the improvement in the hardness and wear resistance of the high-entropy alloys (HEAs) coatings. The decreased segregation of Cu-element along the grain boundaries is mainly attributed to the significant improvement in surface properties of the HEA coatings.     

The reinforcing mechanism of carbon fiber in composite adhesive for bonding carbon/carbon composites

A carbon fiber reinforced adhesive was developed for bonding carbon/carbon composites. The Weibull distribution method was used to analyze the bonding strength data, and the results showed that when the volume fraction of carbon fiber was 6 vol.%, the Weibull modulus was 42.9393 and the bonding strength of the adhesive was 11.3763 MPa. A model was proposed to explain the reinforcement of carbon fiber, and it was found that the strength of adhesive was a cubic function of the volume fraction of carbon fiber, and the function model was consistent with the Weibull data. We investigated that the carbon fiber could bridge adhesive matrix as a bridging effect for releasing the residual stress and inhibiting the extension of micro-crack.     

碳纤维复合材料电子质子综合辐照损伤研究

研究了电子、质子综合辐照条件下碳纤维/环氧复合材料力学性能、质量损失率等性能的变化规律,并采用FT-IR、XPS等对空间环境作用前后的材料进行了分析和表征。结果表明,随辐照注量增加复合材料层间剪切强度呈先上升后下降趋势,质量损失则先快速升高,在2.0×1016cm-2辐照注量后趋于平缓。     

Methods of surface carburizing and alloying steel by means of carbon fiber materials

Carbon fibers and textiles based on them are being used increasingly to reinforce composites. In this article we report the results of inetallographic research on the surface layers formed by passing an electric current through a hardened steel part and a fabric or felt made of a carbon-fiber material on its surface.Vinnitsa Polytechnical Institute. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 1, pp. 35–39, January, 1994.     

Thermal transitions of resveratrol on a carbon black surface

Methods of thermogravimetric analysis, differential scanning calorimetry, and thermal desorption mass-spectrometry are used to study the processes of thermolysis of resveratrol on the surface of graphitized thermal carbon black (GTCB). The results obtained in thermolysis of pure resveratrol and resveratrol adsorbed on GTCB from diethyl ether are compared. The regions of maximum evolution of thermolysis products are determined; their compositions are identified; an increase in thermal stability of resveratrol supported on the surface of graphitized thermal carbon black is observed.     

Effect of carbon fiber surface treatment on Cu electrodeposition: The electrochemical behavior and the morphology of Cu deposits

The relationship between surface functional groups and electrochemical behaviors of polyacrylonitrile (PAN)-based carbon fibers (CFs) differentiated by oxidation treatment in air was studied. The chemical character of the CFs surface was estimated by X-ray photoelectron spectroscopy (XPS) and the electrochemical behavior of treated CFs in CuSO₄ plating solution was studied by electrochemical setup. The influence of functional groups on the morphology of copper deposits was characterized by field-emission scanning electron microscopy (FESEM). It was found that the O/C atomic ratio rose rapidly from 23.05% (as-received carbon fibers) to 42.83% as the oxidation temperature was increased to 400 °C and the content of -CO was the highest. Concentrations and types of the functional groups on CFs surface showed a close connection with the electrochemical response of CFs in CuSO₄ plating bath. It was showed that Cu electrodeposition was the interaction of applied voltage and the reduction of surface functional groups. With the functional groups increased, the quantities of the Cu nuclei increased, further the morphology of deposited Cu was affected.     

碳纤维/层状木材陶瓷的制备与力学性能

为了提升木材陶瓷的力学性能,用液化木材、炭粉和碳纤维等制备增强型层状结构木材陶瓷。探讨了烧结温度、液化木材用量等因素对其结构和力学性能的影响。结果表明,增强型层状木材陶瓷层状结构清晰,摩擦性能良好,且在微观上部分保持了木材天然的孔隙结构特征。同时,增强碳纤维和层状结构的运用能够获得较高强度与较好韧性。当烧结温度为1100℃、炭粉与液化木材质量比为1∶0.75、胶合压力为3 MPa时,其抗弯强度、弹性模量、断裂韧性分别达到了53.90 MPa、2.58 GPa和1.69 MPa·m1/2,与普通木材陶瓷相比均有大幅度提高。     

Electrografting of 3-methyl thiophene and carbazole random copolymer onto carbon fiber: characterization by FTIR-ATR, SEM, EDX

Electrografting of poly(3-methylthiophene-co-carbazole) onto high tenacity (TENAX HTA 5000) carbon fiber was carried out under preparative constant-current electrolysis conditions by electropolymerizing in non-aqueous media. The surface morphology of the electrografted carbon fibers was determined by scanning electron microscopy (SEM). For characterization of the chemical composition of the random copolymer, FTIR reflectance measurements (FTIR-ATR) were performed. The efficiency of the electrocopolymerization on carbon fiber surfaces under preparative constant-current electrolysis conditions as a function of the experimental conditions was evaluated (effect on thickness and morphology).     

Electrochemical and SEM studies of a new implant bioalloy in physiological electrolytes

A new implant Ti–7Al–3V–2Mo–2Fe alloy was elaborated and its behaviour in Ringer–Brown and Ringer solutions (of different pH values) was studied using cyclic potentiodynamic and linear polarisation, electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM) with its link energy dispersive X‐ray system (EDX). Cyclic potentiodynamic polarisation curves revealed that the Ti–7Al–3V–2Mo–2Fe alloy is self‐passivated in Ringer solutions. Pitting corrosion appeared in alkaline Ringer solution but at very electropositive values of the breakdown and pitting protection potentials and it is not possible to develop local corrosion on this alloy, even in extreme functional conditions. EIS spectra at open circuit potential exhibited two phase angles characterising a resistant passive film and some charge transfer reactions. SEM–EDX analysis shows the presence of some aggregates containing complex compounds of calcium, magnesium, phosphor, silicon deposited on the alloy surface.     

A machine tool motorized spindle with hybrid structure of steel and carbon fiber composite

Carbon fiber reinforced plastic (CFRP) is a promising material for enhancing the spindle performance of machine tools because of its high specific stiffness and low thermal expansion. However, when a conventional steel spindle shaft is replaced by a CFRP shaft, the anisotropic property of CFRP makes it difficult to maintain the static stiffness that is equivalent to that of conventional spindles. This study proposes a hybrid structure of steel and CFRP to avoid reduced stiffness of the shaft. Fundamentals of shaft design are described to enable discussion of a favorable steel-CFRP ratio. An experimental evaluation of a developed CFRP spindle is also reported.     

The influence of surface oxide composition and structure on carburization in carburization in carbon monoxide – carbon dioxide

The oxidation and carburization of two 20 Cr 30 Ni alloys with nominally 0 and 0.5 wt % Si have been investigated by cyclic exposure to carbon monoxide and carbon dioxide at 1000°C. In carbon monoxide a chromium oxide film is formed which inhibits further carbon deposition. In carbon dioxide an iron chromium oxide of the spinel type is formed which during subsequent exposure to carbon monoxide acts as a catalyst for carbon deposition. In some areas a breakthrough of the initially formed chromium oxide layer occurs during carbon dioxide treatment. Extensive carbon penetration takes place in these breakthrough areas. The spinel formation and the breakthrough is retarded in the silicon-containing steel owing to the formation of a thin continuous silica layer at the metal-chromium oxide interface. This has a beneficial effect on the carburization resistance. The results also imply that it is possible to lower the catalytic effect of the tube material on carbon deposition or even on coke formation by controlling the surface oxide composition and structure.