Mechanical properties of Cu-based composites reinforced by carbon nanotubes

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铜基自润滑复合材料的电弧烧蚀性能研究

研究了铜-30%(体积分数,下同)石墨、铜-30%二硫化钨和铜-30%二硫化钼3种铜基自润滑复合材料的抗电弧烧蚀性能。结果表明:石墨熔点较高,在电弧放电瞬间主要以氧化的形式损耗,而二硫化钨和二硫化钼则会在电弧放电造成的高温下发生熔化甚至与铜基体发生化学反应,所以铜-30%石墨复合材料的抗电弧烧蚀性能要优于铜-30%二硫化钨和铜-30%二硫化钼复合材料。铜基自润滑复合材料的电弧烧损机制主要有材料的氧化、熔化飞溅、内部化学反应以及疲劳脱落。     

SiO_2粒度对铜基摩擦材料摩擦性能的影响

采用粉末冶金技术制备了铜-石墨-SiO2烧结材料,利用销-盘式摩擦试验机,在摩擦速度为7.8～47.1 m/s时,研究了SiO2粒度与材料摩擦性能的关系。结果表明,随着SiO2粒度的提高,摩擦系数变化不明显,磨损率降低。     

Friction and wear properties of Cu-based self-lubricating composites in air and vacuum conditions

Cu-based self-lubricating materials containing two different solid lubricants (graphite and MoS 2 ) were fabricated by P/M hot pressing techniques. Physical and mechanical properties of the samples were examined. The effects of graphite and MoS 2 contents on friction coefficient and wear rate were investigated by a ring-on-disc wear machine in air and vacuum conditions, respectively. Tribo-films formed on the worn surfaces were characterized by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The results indicated that density, hardness and bending strength all increased with the increasing content of MoS 2 , while the relative density was opposite. Sample B containing 15 vol. pct graphite and 15 vol. pct MoS 2 possessed superior tribological properties both in air and vacuum conditions. However, the tribo-films formed on the worn surfaces of the sample B were greatly discrepant in composition at different testing conditions. In air, the volume ratio of MoS 2 and graphite in the tribo-films is 0.31:1 whereas the ratio in vacuum is 1.07:1.     

炭/炭复合材料航空刹车副的湿态摩擦性能

对两种不同的炭/炭复合材料湿态下的摩擦磨损性能进行对比分析。结果表明:具有粗糙层热解炭的炭/炭刹车副由于其晶格结构较为完善,生长组织择优取向度和各向异性度均高于含有光滑层结构热解炭的炭/炭刹车副。前者的石墨化度及可石墨化能力均大于后者,由于前者的表面缺陷较少,所吸附的水分子较少,因而在湿态下刹车时,其刹车力矩将很快恢复到正常干态刹车时的力矩水平,对环境的适应能力大于光滑层结构的炭/炭刹车副。     

Tribological properties of C/C-SiC composites for brake discs

This study examines the friction and wear of ceramic matrix composites designed for use in automotive brake discs. The composites are produced by reinforcing a SiC matrix with carbon fibers using a liquid silicon infiltration method. C/C-SiC composites with two different compositions are fabricated to examine the compositional effect on the tribological properties. The tribological properties are evaluated using a scale dynamometer with a low-steel type friction material. The results show that the coefficient of friction is determined by the composition of the composite, which affects the propensity of friction film formation on the disc surface. A stable friction film on the disc surface also improves the wear resistance by diminishing the abrasive action of the disc. On the other hand, the friction film formation on the disc is affected by the applied pressure, and stable films are obtained at high pressures. This trend is prominent with discs with high Si content. However, both C/C/-SiC composites show superior performance in terms of the friction force oscillation, which is closely related to brake-induced vibration.     

Tribological properties of graphite- and ZrC-reinforced bulk metallic glass composites

The influence of second-phase reinforcement on the micro-tribological properties of Zr_52.5Cu_17.9Ni_14.6Al₁₀Ti₅ (Vit 105) was investigated by ball-on-disc tests. It was found that monolithic amorphous Vit 105 displays a coefficient of friction (COF) similar to that of 100Cr6 bearing steel. Further, it was seen that adding a low volume content of graphite and especially of ZrC generates a significant decrease in the COF, of up to 50%. Amorphous Vit 105 and its graphite-/ZrC-reinforced composites typically display two regimes of COF. After 100–500 revolutions it drops to about 2/3 of the starting value, and jumps back up to the initial COF are also observed. These transitions take place within the space of about 10 revolutions and are accompanied by a significant change in wear track depth. Investigation of the wear rate indicates that the graphite-/ZrC-reinforced bulk metallic glass composites display an even lower wear rate than 100Cr6 bearing steel.     

硼酸镁晶须增强镁基复合材料的摩擦性能及磨损行为

研究真空气压渗流法制备的硼酸镁晶须增强镁基复合材料(体积分数30%)及其基体合金在液体石蜡润滑条件下的滑动摩擦磨损性能.试验条件为滑动距离2 km,滑动速度0.5、1.0、2.0、3.0和5.0 m/s,载荷5、10、18、25和40 N.结果表明:在润滑条件下,引入增强相MgB2O5能提高复合材料在低载下的耐磨性能.随着载荷的增加,复合材料的磨损由轻微磨损向严霞磨损转变.临界载荷分别为:1 m/s,25N:2m/s,18N:3m/s,10N;5 m/s,5 N.复合材料磨损情况的扫描电了显微分析和观察显示,复合材料在两种摩损阶段的主导磨损机制分别为磨粒和剥层磨损.研究还发现,复合材料由轻微磨损阶段向严重磨损阶段的转变不仪与载荷有关,还与滑动速度有关.     

Tribological properties and thermal-stress analysis of C/C-SiC composites during braking

The tribological properties and thermal-stress behaviors of C/C-SiC composites during braking were investigated aiming to simulate braking tests of high-speed trains. The temperature and structural fields of C/C-SiC composites during braking were fully coupled and simulated with ANSYS software. The results of tribological tests indicated that the C/C-SiC composites showed excellent static friction coefficient (0.68) and dynamic friction coefficient (average value of 0.36). The highest temperature on friction surface was 445 °C. The simulated temperature field showed that the highest temperature which appeared on the friction surface during braking was about 463 °C. Analysis regarding thermal-stress field showed that the highest thermal-stress on friction surface was 11.5 MPa. The temperature and thermal-stress distributions on friction surface during braking showed the same tendency.     

纳米SiO2对铜基摩擦材料摩擦学性能的影响

采用粉末冶金法制备添加0.75%的纳米SiO2(n-SiO2)和0.75%Cu包覆纳米SiO2(Cu/n-SiO2)复合粉体的新型铜基摩擦材料.采用惯性台架实验机,研究比较两种材料与未添加纳米SiO2的材料的摩擦学性能.结果表明:在铜基摩擦材料中添加微量n-SiO2可改善材料的耐磨性和耐热性;添加Cu/n-SiO2的铜基摩擦材料,耐热性提高32%,耐磨性提高2.02倍;添加n-SiO2的摩擦材料,耐热性提高7%,耐磨性提高18%;经铜包覆处理后的n-SiO2对材料性能的影响优于未处理的n-SiO2.     

Tribological evaluation of Fe-B-TiB2 metal matrix composites

Iron and titanium borides have been widely used for the production of metal matrix composites (MMC). The majority of the studies focus on the Fe-TiB₂ and/or the Fe-TiB₂-TiFe₂ region of the ternary Fe-Ti-B diagram, whereas the Fe-TiB₂-Fe₂B area has not yet been systematically studied, although it combines two very hard particles, namely TiB₂ and Fe₂B. This research deals with the wear behavior and tribological evaluation of Fe₂B-TiB₂ MMC layers, which were successfully produced on the surface of plain carbon steel, using the plasma transferred arc (PTA) technique. The counterbody, either tool steel or alumina ball, plays an important role in the wear rate and friction coefficient of the boronized surfaces. The “free” boron content in the Fe-TiB₂-B system, i.e. boron not bound in TiB₂, affects the tribological behavior of the alloyed layers. With steel as the counter-body material, “free” boron content increases the wear rate due to the formation of a more brittle matrix which is easily removed by adhesion, while with the alumina counter-body it has the tendency to decrease the wear rate, as the strengthened matrix can resist better to abrasion. The friction coefficient values for the tool steel ball are smaller than those of the alumina ball, owing to the different wear mechanisms involved.     

CNTs-Cu和C-Cu复合材料的载流摩擦学行为(英文)

采用粉末冶金方法在相同的工艺条件下制备CNTs-Cu和C-Cu复合材料。采用销盘式载流摩擦磨损试验机对两种材料的载流摩擦学行为进行研究。结果表明:铜基复合材料的摩擦因数和磨损率均随着增强体含量的增加而减小,随着电流密度的增加而增大;电流对C-Cu复合材料的影响更加显著;C-Cu复合材料的主导磨损机制是电弧烧蚀和粘着磨损,而CNTs-Cu复合材料的主导磨损机制是粘着磨损和塑性流动变形。     

Dielectric properties of polymer composites with TlInSe2 semiconductor filler

The dielectric properties of polymer composites on the basis of polyethylene and polypropylene with TlInS₂ semiconductor filler are investigated. It is shown that the changes in these properties that were observed are caused by polarization processes occurring on the polymer-filler interface.     

Tribological properties of TiAlN-coated cermets

Ti(C,N)-based cermets were coated with TiAlN using multi-arc ion plating technology. Sliding wear tests were performed on the coated cermets. The microstructure and morphologies of the coated cermets before and after friction and wear tests were characterized. The results show that the TiAlN coating surface was smooth and its root mean square roughness was 16.6 nm. The hardness (HK) of TiAlN coating layers reached approximately 3200 and the critical load (L _c) under which the coating failure occurred was 59 N. The sliding wear test results show that the friction coefficients of the TiAlN-coated cermets were lower than that of the cermets without any coating. Under the same load, the adhesion phenomenon of the counterpart materials on the specimens was improved and the mean friction coefficient increased with increasing sliding velocity. When the sliding velocity was 0.26 m·s⁻¹, the mass of the coated cermets reduced. At the same sliding velocity, the average friction coefficient of the TiAlN-coated cermets was lower under a higher load. The wear mechanisms of the TiAlN-coated cermets were mainly adhesive and abrasive wear.     

Tribological properties of brake friction materials with steel fibers

The tribological properties of brake friction materials with and without steel fibers were investigated. The focus of this study was determining the effect of steel fibers on the speed sensitivity of the friction coefficient. The speed sensitivity of the friction coefficient is closely associated with the stick-slip phenomenon. The results indicate that the friction material containing steel filbers was more sensitive to sliding speed, exhibiting a highly negative μ-ν relation. In particular, the friction material with steel fibers showed a larger vibration amplitude during brake applications, suggesting that the μ-ν relation was strongly related to the friction-induced vibration. On the other hand, the wear resistance of the friction materials containing steel was significantly better than that without steel fibers, suggesting longer service life. A possible mechanism of the stick-slip by the steel fibers is discussed in terms of the physical properties of the steel fiber and the gray iron rotor.     

Tribological behavior of Ni/Sn metallic multilayer composites

The tribological behavior of Ni/Sn multilayer composites was studied. Composites with varied layer thickness and tin volume fraction were prepared by electrodeposition. The coefficient of friction and wear rate of these composites were characterized by pin-on-disk and block-on-ring tests. Both results suggested that soft tin acted as a solid lubricant between the contacting surfaces. Tin-rich films were detected on both the specimen and the steel wear pair surfaces, and wear resistance greatly depended on the thickness, area coverage, composition, and stability of this interfacial film. Specimens with a lower tin content and/or a thinner layer spacing exhibited enhanced wear resistance compared to those with a higher tin content and/or thicker layers. This was attributed to both the solid-lubricating effect of the tin and the enhanced mechanical properties of the multilayered composites.     

Preparation and properties of hot-pressed NbMo-matrix composites reinforced with ZrB2 particles

The NbMo-matrix composites reinforced with (0–60 vol%) ZrB₂ were fabricated by hot-pressing at 2400 °C for 10 min under a pressure of 50 MPa in dynamic vacuum in the induction heating furnace specially designed in our institute. The optimum ZrB₂ content in NbMo solid solution was determined to be 30 vol% for excellent comprehensive mechanical property. NbMo-30 vol% ZrB₂ has the highest density of 99.63%, the most uniform microstructure, high fracture toughness of 5.75 MPa m^1/2. The highest ZrB₂ concentration that reacts with NbMo solid solution is at the range of 30 to 45 vol%. The types of the formed niobium borides were decided by the original ratio of Nb to B. The distribution of Mo and Zr was mutually exclusive in low ZrB₂ content composites, however, there was Mo₂Zr in high ZrB₂ content composite. Except for NbMo-45 vol% ZrB₂, the compressive strength increased with ZrB₂ content (from 927.09 MPa to 1635.91 MPa). The Young's modulus values were directly proportional to ZrB₂ content. The fracture toughness (from 6.34 MPa m^1/2 to 3.99 MPa m^1/2) was inversely proportional to ZrB₂ content. The big residual ZrB₂ particles in high ZrB₂ content samples such as NbMo-45 vol% ZrB₂ and NbMo-60 vol% ZrB₂ was the main reason for nonhomogeneous microstructure, low density (94.09% and 94.83%, respectively) and low fracture toughness (4.58 MPa m^1/2 and 3.99 MPa m^1/2, respectively).     

Room—temperature mechanical properties of WSi2／MoSi2 composites

Five Kinds of WSi2/MoSi2 composites were successfully prepared by mechanical alloying,IP and high temperature sintering techniques.And their hardness and fracture toughness were measured by the Vickers indentation fracture mode through an Hv-10A type sclerometer.The microstructure and morphology were investigated by a JSM-5600IV scanning electron microscope.Results show that the addition of 50% WSi2(in mole fraction)has remarkable hardening and toughening effects on the MoSi2 matrix.whose hardness value and fracture toughness value are increased about 60% and 86%,respectively.For WSi2/MoSi2 comosite,the hardening mechanisms are fine-grain and the second phase particles strengthening,and the toughening mechanisms include fine-grain,grain drawing,crack deflection,microbridge and bowing toughening.