纳米碳管/铝基复合材料的制备及摩擦磨损性能研究

利用粉末冶金法制备纳米碳管/铝基复合材料,研究不同纳米碳管含量对复合材料硬度和稳态摩擦磨损行为的影响,采用扫描电子显微镜观察复合材料的磨损表面形貌,并对其磨损机制进行探讨.结果表明:随着纳米碳管质量分数的增加,复合材料的硬度呈现先增大而后减小的趋势,含质量分数为2%的纳米碳管复合材料硬度比铝增加约80%;复合材料的摩擦系数逐渐降低,磨损率先减小而后增大;含质量分数为1%的纳米碳管复合材料磨损机制为磨粒磨损和粘着磨损,而含质量分数为2%的纳米碳管复合材料以剥层磨损和疲劳磨损为主.     

高浓度过氧化氢中AlCoCrFeNiCu 的摩擦学性能研究

为研究AlCoCrFeNiCu高熵合金在强氧化的过氧化氢介质中的摩擦学性能,采用销盘磨损试验机测试了AlCoCrFeNiCu合金与3种工程陶瓷组成摩擦副在90％过氧化氢介质中的摩擦学性能,采用SEM、EDS、白光共焦显微镜等分析了磨损表面,并且探讨了高熵合金与3种陶瓷配副在高浓度过氧化氢中的磨损机理.结果表明:在高浓度过氧化氢中,AlCoCrFeNiCu合金与碳化硅和氮化硅陶瓷配副具有较低的摩擦系数和较小的磨损;AlCoCrFeNiCu/ZrO₂摩擦副的主要磨损机制为黏着磨损和磨粒磨损,同时伴随有氧化磨损;AlCoCrFeNiCu/SiC摩擦副和AlCoCrFeNiCu/Si₃N₄摩擦副的主要磨损机制为抛光型氧化磨损并伴随有轻微的三体磨粒磨损;AlCoCrFeNiCu/Si₃N₄摩擦副还伴随有边界润滑效应.     

位移幅值对690合金管/405不锈钢块切向微动磨损特性的影响

采用自制的微动磨损试验机,开展了690合金管/405不锈钢的切向微动磨损试验,研究了位移幅值(15、30、80和200 μm)对其微动磨损特性的影响. 试验结果表明:当位移幅值改变时,微动运行状态会发生改变. 当位移幅值为15 μm时,微动状态为部分滑移区,此时摩擦系数最小,磨损率最低,微动损伤最轻微;当位移幅值为30 μm时,微动运行于混合区,摩擦系数明显高于部分滑移区;而当位移幅值为80和200 μm时,微动运行于完全滑移区,稳定阶段的摩擦系数与混合区的接近. 总体而言,随着位移幅值的增大,磨痕宽度增大,磨损加剧,磨损体积增加. 部分滑移区的磨损机制主要为黏着磨损和剥层,混合区主要的磨损机制为剥层,而完全滑移区的磨损机制主要为剥层磨损和磨粒磨损.      

内氧化法制备Al2O3/Cu复合材料电滑动磨损性能的研究

采用内氧化法制备Al2O3/Cu复合材料,在自制电磨损试验机上评价Al2O3/Cu复合材料的磨损性能,采用扫描电子显微镜观察Al2O3/Cu复合材料的磨损表面形貌,用能谱仪对其磨损表面主要元素进行分析并探讨其磨损机制.结果表明:在相同试验条件下,Al2O3/Cu复合材料的磨损性能明显优于Cu-0.36Cr-0.06Zr合金,Cu-0.36Cr-0.06Zr合金的磨损率较0.40%Al2O3 /Cu复合材料的磨损率高1倍多;在无加载电流条件下,Al2O3/Cu复合材料的磨损机制为粘着磨损和磨粒磨损;在载流条件下其磨损机制主要以粘着磨损为主,并随着电流强度的增加,粘着磨损程度加重,Al2O3/Cu复合材料表面的粘着物主要来自于铜基粉末冶金滑块;Cu-Cr-Zr合金在无加载电流条件下的磨损机制主要为粘着磨损和磨粒磨损,在载流条件下主要为粘着磨损、磨粒磨损及电烧蚀磨损.     

γN相/Si3N4陶瓷球摩擦副在干摩擦条件下的磨损机制转变图

采用等离子体源渗氮技术在AISI 316奥氏体不锈钢表面制备γN相层.研究了γ_N相层/Si_3N_4陶瓷球摩擦副在球-盘式磨损仪、载荷2~8 N、滑动速度0.15~0.22 m/s干摩擦条件下的磨损行为,基于详细的磨痕表面和磨屑显微分析,通过响应面分析法建立γ_N相层在此状态下的磨损机制转变图.结果表明:γ_N相层在低载荷下的磨损机制主要是氧化磨损;而在较高载荷下的磨损机制主要是塑性变形和磨粒磨损.     

石墨及氧化铝增强AZ91D-Cex基复合材料的磨损性能研究

采用预制体和挤压铸造结合法制备以AZ91D-Cex镁合金为基体,Al2O3短纤维和石墨颗粒混杂增强复合材料,分析不同稀土含量下复合材料的显微组织并测量其硬度,同时考察载荷对复合材料磨损性能的影响.结果表明:复合材料中石墨和Al2O3短纤维分布均匀,与基体结合紧密,稀土Ce沿石墨和Al2O3短纤维的边界富集,其结构为Al3Ce相;复合材料的硬度随稀土含量增加而提高,其中含1.0?合金复合材料的硬度最高;复合材料的磨损率随着稀土含量增加而降低,在20N时3种复合材料的磨损率差别不大,在180N时,含1.0Ce合金的耐磨性最佳.这是由于石墨作为润滑相对摩擦表面起到润滑作用,同时稀土强化相Al3Ce的热稳定性较好,在高载荷时具有较好承载能力,延迟了磨损表面由轻微磨损向剥层磨损的转变.在低载荷时复合材料的磨损机制为磨粒磨损和氧化磨损,在高载荷时为剥层磨损.     

玻璃纤维增强MC尼龙复合材料的摩擦磨损性能研究

通过碱催化阴离子聚合反应制备玻璃纤维增强单体浇铸尼龙复合材料(GFMCPA),在MM-200型摩擦磨损试验机上研究了在干摩擦和水润滑条件下,不同玻璃纤维含量对尼龙复合材料摩擦磨损特性的影响,并借助扫描电子显微镜观察其磨损表面形貌.结果表明:玻璃纤维含量对尼龙复合材料的摩擦性能具有显著影响;玻璃纤维质量分数达到30%后复合材料具有较好的耐磨性;在水润滑条件下,复合材料的摩擦系数和磨损量较干摩擦时大幅度降低;玻璃纤维含量低的尼龙复合材料的磨损机制主要为粘着磨损和磨粒磨损;玻璃纤维含量高的尼龙复合材料的粘着磨损减少,磨损机制主要表现为磨粒磨损和疲劳磨损.     

润滑条件下短纤维增强镁基复合材料的摩擦磨损行为研究

采用挤压浸渍预制件工艺制备了氧化铝短纤维增强镁基复合材料,并探讨了纤维取向对润滑条件下复合材料摩擦磨损行为的影响.结果表明:挤压浸渍工艺制备的镁基复合材料具有纤维二维择向分布,不同纤维分布对复合材料在润滑条件下的耐磨性能和磨损机制有较大影响.滑动方向垂直于纤维排列方向时,复合材料的磨痕深度小于平行方向,但相对应的钢球的磨损量则高于平行方向.滑动方向垂直于纤维排列方向时复合材料的磨损机制主要包括纤维破碎和基体的磨粒磨损;滑动方向平行于纤维排列方向时复合材料的磨损机制主要表现为纤维剥落和磨粒磨损.     

Mo/Al2O3复合材料的耐磨性

无压烧结制备了不同组分的Mo/Al2O3复合材料样品,对样品的磨损行为和磨损机理进行了研究,并用电子探针分析了其磨损形貌.结果表明:Mo/Al2O3复合材料的磨损率随Mo含量的增加呈上升趋势,在30vol.%Mo时出现峰值;摩擦系数随着Mo含量的增加而增大,20vol.%Mo样品的摩擦系数较小;Mo含量不超过60%时,当出现Mo的连续相或者Al2O3的连续相时复合材料表现出较好的耐磨性;Mo含量较低时磨损机理表现为脆性脱落,而Mo含量较高时材料的磨损机理主要为磨粒磨损.     

后热处理对304不锈钢激光熔覆Ni60/h-BN自润滑耐磨复合涂层组织和摩擦学性能的影响

采用激光熔覆技术在304不锈钢表面制备了Ni60/h-BN自润滑耐磨复合涂层,对涂层在600℃(去应力退火)进行1 h和2 h热处理,分析了热处理前后复合涂层的显微组织、硬度和摩擦学性能的变化.结果表明:三种涂层中,热处理1 h后涂层的显微硬度最大(最高值HV0.5765.0),在10 N干摩擦条件下,其摩擦系数为0.39,磨损率为3.37×10~(–6)mm/(Nm),该涂层表现出最好的耐磨减摩性能,磨损机理主要表现为轻微的磨粒磨损;未热处理的涂层摩擦系数为0.53,磨损率为6.39×10~(–6) mm/(Nm),磨损机理主要表现为脆性断裂、黏着磨损和磨粒磨损;热处理2 h后的涂层摩擦系数为0.39,磨损率为5.29×10~(–6)mm/(Nm),磨损机理主要表现为磨粒磨损和轻微黏着磨损.在本文试验条件下,后热处理1 h可有效提高激光熔覆自润滑耐磨涂层的硬度并改善其耐磨减摩性能.     

Spatiotemporal variations of PM2.5 and PM10 concentrations between31 Chinese cities and their relationships with SO2,NO2,CO and O3

The variations of mass concentrations of PM_2.5,PM₁₀,SO₂,NO₂,CO,and O₃ in 31 Chinese provincial capital cities were analyzed based on data from 286 monitoring sites obtained between March 22,2013 and March 31,2014.By comparing the pollutant concentrations over this length of time,the characteristics of the monthly variations of mass concentrations of air pollutants were determined.We used the Pearson correlation coefficient to establish the relationship between PM_2.5,PM₁₀,and the gas pollutants.The results revealed significant differences in the concentration levels of air pollutants and in the variations between the different cities.The Pearson correlation coefficients between PMs and NO₂ and SO₂ were either high or moderate(PM_2.5 with NO₂:r=0.256-0.688,mean r=0.498;PM₁₀ with NO₂:r = 0.169-0.713,mean r = 0.493;PM2.5 with SO₂:r= 0.232-0.693,mean r=0.449;PM₁₀ with SO₂:r = 0.131-0.669,mean r=0.403).The correlation between PMs and CO was diverse(PM_2.5:r = 0.156-0.721,mean r=0.437;PM₁₀:r=0.06-0.67,mean r= 0.380).The correlation between PMs and O₃ was either weak or uncorrelated(PM_2.5:r--0.35 to 0.089,mean r=-0.164;PM₁₀:r=-0.279 to 0.078,mean r=-0.127),except in Haikou(PM2.5:r=0.500;PM₁₀:r-0.509).     

Kinetics of ultrafine coating of SiO2 nanoparticles, suspended in non-thermal CH4/C2H6 plasma

Capacitively coupled RF discharges in methane and ethane (1000–3000 Pa, 5–15 W/cm³) were used for the in-flight coating of SiO₂ nanopowders (NP) with an a-C:H layer [A. Kouprine, F. Gitzhofer, M. Boulos, A. Fridman, Polymer-like C:H thin film coating of nanopowders in capacitively coupled RF discharge, Plasma Chemistry and Plasma Processing 24 (2) (2004) 189–215]. In this present work a model of the chemical kinetics of this plasma processing has been developed, based on the GRI-Mech 3.0 mechanism [G.P. Smith, D.M. Golden, M. Frenklach, Gas Research Institute, Detailed chemical reaction mechanism. Available from: ], and calculations are performed, using the Chemkin-II code. The model includes the formation of two solid phases: an amorphous C:H coating, deposited on the suspended NP, and soot, incepted in the gas phase. Non-equilibrium plasma effects are taken into account by the rates of radical species’ production, using the reference data on the “G-value”. The CH₃ and H species appear to have key roles in surface activation and the nanofilm growth. The results demonstrate the competitive character of the formation of the two solid phases: the C:H coating is dominant under T_gas < 1400–1600 K, depending on the conditions, and soot commencing to dominate at higher temperatures. This division corresponds to the passage from non-thermal plasma conditions, with the dominance of single-valent radicals and solid phase growth on the substrate only, to the plasma thermalisation with the formation of two-valent radicals and v. inception of the solid phase. The results are validated experimentally by the observation of soot formation as a function of the gas temperature, by the mass spectrograph data on the gas composition after plasma reforming, and by the reference data on coating growth rates and induction times for soot formation.     

稀土钇对Ni-W-ZrO2复合镀层性能的影响

通过脉冲电沉积技术在铝合金基体表面制备了Ni-W-ZrO₂复合镀层,利用光学显微镜、扫描电镜、X射线衍射仪、能谱仪、维氏硬度仪、电化学工作站和马弗炉等设备分别对复合镀层的截面形貌、元素分布、表面硬度、耐蚀性和抗高温氧化性分别进行了表征和测试,研究了Y（NO₃）₃添加量对复合镀层性能的影响.研究结果表明：所制备复合镀层截面平整、成分分布均匀,基体与镀层之间结合良好,ZrO₂颗粒弥散分布于Ni-W基质金属之中,镀层厚度约为130 μm;Y（NO₃）₃的加入能显著提高复合镀层的硬度、抗高温氧化性和耐蚀性;当硝酸Y添加量为1.5 g/L时,Ni-W-ZrO₂复合镀层的综合力学性能达到最佳.     

Measurement of propagation speeds in adiabatic cellular premixed flames of CH4 + O2 + CO2

Experimental measurements of the propagation speed of adiabatic flames of methane + oxygen + carbon dioxide are presented. The oxygen content O₂/(O₂ + CO₂) in the artificial air was 31.55% and 35%. Non-stretched flames were stabilized on a perforated plate burner at atmospheric pressure. A heat flux method was used to determine propagation speeds under conditions when the net heat loss of the flame is zero. Under specific experimental conditions the flames become cellular; this leads to significant modification of the flame propagation speed. The onset of cellularity was observed throughout the stoichiometric range of the mixtures studied. Measurements in cellular flames are presented and compared with those for laminar flat flames. Cellularity disappeared when the flames became only slightly sub-adiabatic. Visual and photographic observations of the flames were performed to quantify their cellular structure. Increasing the oxygen content in the artificial air and increasing the temperature of the burner plate led to increase of the number of cells observed.     

纳米SiO2/CeO2复合磨粒的制备及其抛光特性研究

以尿素[CO(NH2)2]、(NH4)2Ce(NO3)6和SiO2为原料,采用均相沉淀法制备1种新型纳米SiO2/CeO2复合磨粒,通过X射线衍射仪、X射线光电子能谱仪、飞行时间二次离子质谱仪和扫描电子显微镜等分析手段对其结构进行表征,并将SiO2/CeO2复合磨粒配置成抛光液在数字光盘玻璃基片上进行化学机械抛光试验.结果表明所制备的SiO2/CeO2复合磨粒的平均晶粒度为19.64 nm,粒度分布均匀;经过1 h抛光后,玻璃基片的平均表面粗糙度(Ra)由1.644 nm降至0.971 nm;抛光后玻璃基片表面变得光滑、平坦,表面微观起伏较小.     

Group properties of utt=[F(u)ux]x

The group properties and the associated Lie algebra are developed for the subject quasilinear wave equation, for arbitrary f[fεC²(R), f > 0, f ≠ 0]. From the resulting information sets of explicit invariant solutions are constructed for wave propagation in gases and for the transonic equation.     

Measurement of the concentration diffusion coefficient for Ne-Ar, Ne-Xe, Ne-H2, Xe-H2, H2-N2 and H2-O2 gas systems

The concentration diffusion coefficient, D ₁₂, is measured for the equimolar mixtures of Ne-Ar, Ne-Xe, Ne-H₂, Xe-H₂, H₂-N₂ and H₂-O₂ binary gas systems in a two-bulb metal apparatus in the temperature range 0 C to 100 C. These values are compared with the existing data on these systems and with the predictions of the kinetic theory in conjunction with the modified Buckingham exp-six potential. Unlike the thermal diffusion coefficient, with the simple theory it is possible to predict D ₁₂ within a few percent even for systems involving polyatomic gases. The smoothed experimental D ₁₂ values are also used to obtain data for the coefficients of viscosity and thermal conductivity at round temperatures and compositions for these systems.Nomenclature C ₂ ^t relative amount of a gas in the mixture in the bulb 2 at an instant t - C ₂ relative amount of the same gas in the mixture in the bulb 2 at equilibrium - D ₁₂ diffusion coefficient - X ₁ mole-fraction of the heavier component in the mixture - _mix viscosity coefficient - _mix thermal conductivity coefficient     

Structure cellulaire de la détonation des mélanges H2–NO2/N2O4Cellular structure of the detonation of gaseous mixtures H2–NO2/N2O4

Calculations of the detonation reaction zone of gaseous reactive mixtures of NO₂/N₂O₄ as oxidizer and H₂, CH₄ or C₂H₆ as fuel, in the range of equivalence ratio Φ between 0.5 and 2, show that, for Φ?1, the chemical energy is released in two distinct and successive exothermic steps with different chemical induction times. The first exothermic stage is mainly due to the reaction NO₂+H→NO+OH, NO being the main oxidizer of the second one.The experimental study conducted on the same range of equivalence ratio (0.5?Φ?2) shows that, for Φ?1, the detonation wave of these mixtures contains a double set of cellular structures. A similar result had already been obtained with the detonation of gaseous Nitromethane, the NO₂ group being here included in the molecule. Consequently, the oxidizer NO₂ being either initially separated from the fuel or included inside the molecule of a monopropellant (Nitromethane) is responsible, because of its specific chemical kinetics, of a chemical energy release in two main steps and of the existence of a double cellular structure in the detonation wave for the same range of equivalence ratio. These results reinforce the assumption that the cellular structure of the detonation finds its origin in the strong rates of chemical energy release inside the reaction zone. To cite this article: F. Joubert et al., C. R. Mecanique 331 (2003).     

开放空间H2/CH4/空气爆炸实验与数值模拟研究

近年来氢的使用范围逐渐发展到各个领域, 含氢多元混合物气体在工业生产及生活燃料中被普遍使用. 为了保障含氢气体在生产、运输、使用等各个环节的安全性, 构建了开放空间混合气体爆炸测试实验系统, 研究了H₂/CH₄/空气混合气体爆炸压力及火焰传播特性, 给出了不同氢摩尔分数(100%, 75%, 66.67%, 50%, 33.33%)、混合气体当量比(0.8, 1.0, 1.1, 1.2, 1.4)、可燃云团尺寸(1 m3, 4 m3, 8 m3)及障碍物约束等因素对混合气体爆炸压力及火焰的影响规律. 基于经典TNT当量法, 建立了考虑混合气体组分比及可燃云团尺寸的最大爆炸超压预测模型, 修正了爆炸火焰传播半径理论模型. 结合高精度数值模拟技术揭示了加气站内建筑结构对混合气体爆炸的影响. 研究表明, 氢气的加入能够明显增强气体爆炸强度, 最大爆炸超压、火焰传播速度均随氢摩尔分数的增加而增大, 随当量比的增大先增大后减小, 当量比为1.1~1.2时最大; 通过对大尺度混合气体爆炸数值仿真与分析发现, 加气站内不同建构筑物条件下爆炸火焰传播距离、传播速度、最大爆炸超压等关键参数明显不同, 顶部和背部同时约束时, 爆炸伤害范围及事故后果最严重, 因此在划定加气站安全距离时, 应充分考虑不同建筑结构的影响.      

二硫化钼/硫化锌纳米粉体的制备及其改性聚酰亚胺复合材料的摩擦学性能研究

采用一步水热法设计制备了二硫化钼/硫化锌(MoS₂/ZnS)纳米杂化体,并利用热压成型技术得到聚酰亚胺/二硫化钼/硫化锌(PI/MoS₂/ZnS)复合材料. 采用扫描电子显微镜、透射电子显微镜、X射线衍射仪以及光电子能谱仪对所制备材料的形貌和化学组成进行表征,结果表明MoS₂纳米薄片均匀致密地包覆在ZnS纳米颗粒表面. 热重分析和差示扫描量热曲线结果表明,MoS₂/ZnS纳米杂化体的引入显著地提升了PI基体的热稳定性能. 摩擦磨损测试结果表明,三种填料(MoS₂,ZnS和MoS₂/ZnS)均能有效改善PI基体的摩擦学性能,其中MoS₂/ZnS纳米杂化体的增强效应最为显著,这主要归因于MoS₂纳米片和ZnS纳米粒子之间的协同增强效应. 当MoS₂/ZnS纳米杂化体的质量分数为1.5%时, PI/MoS₂/ZnS复合材料的摩擦学性能达到最优,相较于纯的PI,复合材料的摩擦系数和磨损率分别下降了15. 9%和34. 3%.