NH4F浓度对镁合金表面微弧氧化制备氟化物膜层结构和性能的影响

目的 考察乙二醇-氟化铵电解液中氟化铵浓度对镁合金表面微弧氧化制备氟化物膜层结构和性能的影响,提高镁合金氟化物膜层的耐腐蚀性能。方法 在含不同浓度NH4F的EG-NH4F电解液中,采用微弧氧化的方法制备氟化物膜层,NH4F质量浓度分别为40、60、80、100、120 g/L。通过扫描电子显微镜(SEM)、X射线能量色散谱仪(EDS)和X射线衍射仪(XRD),对膜层表面微观形貌和成分组成进行分析,并通过电化学测试表征了膜层的腐蚀防护性能,通过盐雾试验评估了膜层长效防腐蚀行为,通过SEM和EDS表征了腐蚀形貌和腐蚀产物。结果 在EG-NH4F中制备膜层的物相组成主要是MgF2。随着NH4F浓度的提高,微弧氧化的起弧电压与工作电压均逐渐减小,膜层中氟含量逐渐增加,膜层的孔径减小,孔数量分布更加均匀,膜层表面粗糙度降低。质量浓度为100 g/L NH4F的膜层自腐蚀电流密度(Jcorr)为2.226×10^‒7 A/cm²,较镁合金基材降低了1个数量级,极化电阻Rp增大到90.156 kΩ.cm²,其阻抗模量|Z|f=0.01 Hz=8.55×10⁵ Ω.cm²,与镁合金基材的阻抗模量|Z|f=0.01 Hz=8.86×10² Ω.cm²相比,提高了3个数量级。结论 微弧氧化处理能够显著改善AZ31镁合金的腐蚀防护性能。NH4F浓度的增加有利于提高膜层的耐腐蚀性能,质量浓度为100 g/L NH4F的膜层耐腐蚀性能最优。     

Tribological behavior of poly (phenyl p-hydroxybenzoate)/polytetrafluoroethylene composites filled with hexagonal boron nitride under dry sliding condition

The sliding friction and wear behavior of polytetrafluoroethylene (PTFE) composites filled with poly (phenyl p-hydroxybenzoate) (PHBA) and hexagonal boron nitride (h-BN) was investigated with a pin-on-disc tester. The tensile properties, ball indentation hardness, impact strength and thermal diffusivity were measured. The test results in this paper indicate that the tensile strength, elongation at break, and impact strength decreased, however, the ball indentation hardness and thermal diffusivity were increased when the content of h-BN was increased. PTFE composites filled with 20 wt% PHBA and 20 wt% h-BN exhibited a comparative friction coefficient to pure PTFE. Meantime, the wear rate of the composite decreased about 15 times compared to pure PTFE. The synergistic effect of h-BN with low friction and PHBA with high bearing ability promoted the low friction coefficient and wear rate of h-BN/PHBA/PTFE composites.     

碳基薄膜固液复合润滑研究现状

摩擦和磨损制约着机械系统的高可靠、长寿命服役,随着科学技术的快速发展,单一的固体或液体润滑系统已经无法满足工业应用中对机械部件的摩擦学性能要求.因此,研究人员对固液相复合润滑体系展开了大量研究,碳基薄膜因具有优异的摩擦学性能而常被用于组成固液复合润滑体系.对碳基薄膜固液复合润滑体系的研究进行了回顾,从碳基薄膜/油复合润滑、碳基薄膜/离子液体复合润滑、碳基薄膜/水复合润滑、碳基薄膜/润滑剂/纳米添加剂复合润滑,以及表面织构碳基薄膜和摩擦过程中生成碳材料的特殊碳基材料复合润滑六个体系对碳基薄膜固液复合润滑进行了综述.碳基薄膜/润滑油复合润滑无论是在大气还是在真空中都表现出优异的摩擦学性能,碳基薄膜/离子液体复合润滑对于提高在苛刻条件下服役的机械运动部件的摩擦学性能具有指导意义和广泛的应用前景.润滑添加剂的使用,可以在碳基薄膜/润滑油复合润滑体系的基础上进一步提高摩擦学性能,过渡金属氮化物/润滑油摩擦催化生成碳材料为进一步发现和发展不同的先进润滑和保护材料提供了前景.最后总结了目前研究领域中存在的一些问题,并对未来发展方向进行了展望.     

Toward Robust Macroscale Superlubricity on Engineering Steel Substrate

“Structural superlubricity” is an important fundamental phenomenon in modern tribology that is expected to greatly diminish friction in mechanical engineering, but now is limited to achieve only at nanoscale and microscale in experiment. A novel principle for broadening the structural superlubricating state based on numberless micro-contact into macroscale superlubricity is demonstrated. The topography of micro-asperities on engineering steel substrates is elaborately constructed to divide the macroscale surface contact into microscale point contacts. Then at each contact point, special measures such as pre-running-in period and coating heterogeneous covalent/ionic or ionic/ionic nanocomposite of 2D materials are devised to manipulate the interfacial ordered layer-by-layer state, weak chemical interaction, and incommensurate configuration, thereby satisfying the prerequisites responsible for structural superlubricity. Finally, the robust superlubricating states on engineering steel–steel macroscale contact pairs are achieved with significantly reduced friction coefficient in 10⁻³ magnitude, extra-long antiwear life (more than 1.0 × 10⁶ laps), and good universality to wide range of materials and loads, which can be of significance for the industrialization of “structural superlubricity.”     

Sintering and densification mechanisms of tantalum carbide ceramics

Dense tantalum carbide (TaC) ceramics were prepared using TaC nanopowder via spark plasma sintering (SPS). The effects of the sintering temperature and applied pressure on the densification and grain growth behaviour of TaC ceramics were investigated. The results showed that high temperature and pressure promoted sintering densification, while their increase caused an increase in the grain size of TaC ceramics. A highly dense TaC ceramic (∼97.19%) with a fine grain size of 2.67 μm was obtained by sintering at 1800 °C for 10 min under 80 MPa. The Vickers hardness, Young's modulus and fracture toughness were 15.60 GPa, 512.66 GPa and 3.59 MPa·m^1/2, respectively. The densification kinetics were investigated using a creep deformation model. Diffusion and grain boundary sliding were proven to be the dominant densification mechanisms based on the stress and grain size exponents combined with the microstructural characteristics. The apparent activation energy of the mechanism controlling densification was 252.94 kJ/mol.     

非晶含氢碳薄膜本征结构对退火行为的影响

目的 为在高温工况下服役的含氢碳(a–C:H)薄膜的制备提供新思路。方法 首先利用DP–PECVD和BiP–PECVD两种方法分别在Si基底上制备了两种本征结构不同的a–C:H薄膜,分别在350、450、550、650 ℃下进行退火处理。通过纳米硬度、X射线光电子能谱、傅里叶转变红外光谱、激光共聚焦拉曼光谱、场发射扫描电镜及CSM摩擦试验机等,分别评价了未退火和不同退火温度下两种不同结构a–C:H薄膜的结构、表面形貌、力学及摩擦学等性能。研究了不同本征结构a–C:H薄膜对退火行为的影响。结果 DP–PECVD方法在制备a–C:H薄膜(A薄膜)的过程中具有更高的沉积速率,是BiP–PECVD法(B薄膜)的1.52倍。随着退火温度的增加,两种方法制备的a–C:H薄膜均发生H脱附,但是A薄膜的脱H转变点为450 ℃,B薄膜的脱H转变点为350 ℃。DP–PECVD法制备的a–C:H薄膜在H脱附过程中更容易形成sp³–C,而BiP–PECVD法制备的a–C:H薄膜在此过程中形成sp³–C和sp²–C杂化键的概率基本相同。BiP–PECVD法制备的a–C:H薄膜在退火过程中更容易失去H,且在450 ℃以上出现大面积剥离,摩擦失效。而DP–PECVD法制备的碳薄膜则表现出更好的热和摩擦学稳定性,在350~650 ℃均可保持薄膜的完整性,并且在350~ 550 ℃退火后保持低至约0.06的摩擦因数。结论 DP–PECVD方法制备的a–C:H薄膜具有更好的热稳定性、力学稳定性及摩擦学稳定性。     

Scratch induced failure of plasma sprayed alumina based coatings

A set of plasma sprayed coatings were obtained from three alumina based top coat and two bond coat powders. Scratch test was undertaken on these coatings, under constant and linearly varying load. Test results include the lateral force data and scanning electron microscope (SEM) images. Failure occurred by large area spallation of the top coat and in most cases tensile cracks appeared on the exposed bond coat. The lateral force showed an increasing trend with an increase in normal load up to a certain point and beyond this, it assumed a steady average value. The locations of coating spallation and occurrence of maximum lateral force did not coincide. A bond coat did not show a significant role in determining the scratch adhesion strength.     

电机轴承防护措施及Al2O3陶瓷绝缘涂层研究现状

讨论了避免电机轴承电蚀失效的主要防护措施,包括安装接地碳刷疏导轴电流、使用绝缘轴承截断轴电流这两类方式,并对其优缺点分别进行了阐述.针对绝缘轴承,着重分析了Al2O3陶瓷涂层的热喷涂工艺(粉末粒径、喷涂参数等)、涂层结构(表面形貌与微观组织)以及涂层性能(力学性能、摩擦性能、绝缘性能)三者间的关系,介绍了通过掺杂其他金属阳离子氧化物或纳米结构粉末对涂层性能进行改性的方法.在此基础上,对绝缘轴承Al2O3陶瓷涂层制备技术存在的难点进行了分析,总结了存在的主要问题.最后对绝缘轴承Al2O3陶瓷涂层制备技术的发展趋势进行了展望.     

Influence of different introduction modes of metal Ag into plasma sprayed Al2O3 coating on tribological properties

Al₂O₃ coating and Al₂O₃/Ag (10%) composite coating were prepared on the surface of GH4169 superalloy by the atmospheric plasma spraying technology. And an in-situ synthesis method was applied to introduce the Ag particles into a part of Al₂O₃ coatings to obtain Al₂O₃/Ag(synthesis) composite coating. Then, the microstructure and mechanical properties of these three Al₂O₃-based coatings were systematically studied in this work. In order to reveal the lubrication characteristics of Ag, their friction tests were carried out at room temperature (RT), 400 °C, 600 °C and 800 °C, respectively. The results showed that both microstructure and mechanical properties of Al₂O₃/Ag(synthesis) composite coating were better than that of Al₂O₃/Ag (10%) composite coating because many pores and cracks produced during the direct spraying. Although the friction coefficients of two kinds of composite coatings were close to that of Al₂O₃ coatings at RT, their wear rates were both greatly decreased due to the introduction of Ag. In addition, the lubricating performance of Ag was not enough to reduce their friction coefficients when friction temperature is lower than 600 °C. However, the friction coefficients of these composite coatings were both reduced to about 0.3 at 800 °C . At this time, the Al₂O₃/Ag(synthesis) composite coating also exhibited a lower wear rate because of its dense microstructure and excellent mechanical properties.     

一种工业机器人用高性能润滑脂的开发与应用研究

根据摆线针轮(RV)减速器的运行特点与摩擦副运行工况,选择合成烃基础油作为主要基础油,同时加入部分环烷基基础油以改善基础油与皂的相容性,增加部分增黏剂来保证产品的附着力和基础油的黏度指数;为提升润滑脂的抗氧化性及减摩和极压性能,选择氢过氧化物分解型抗氧剂(硫酯型)与自由基捕获型(胺型、酚型)抗氧剂复合抗氧剂,选择MoDTC为主的复合摩擦磨损添加剂。对该润滑脂在机器人负荷2 100 N、满行程、室温((23±2)℃)、24 h不间断运行的极端运行条件下,进行了为期8 000 h的性能测试。在测试过程中机器人运行情况平稳、定位准确,表明该润滑脂对减速器的润滑保护性能优良,满足机器人使用要求。