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.     

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.     

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.     

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。     

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.     

类富勒烯结构对含氢碳膜摩擦学性能的影响

目的研究类富勒烯结构含氢碳膜的摩擦学性能及润滑机理。方法采用闭合场非平衡反应磁控溅射技术,通过调节靶电流制备出类富勒烯结构含氢碳膜(FL-C:H)与非晶含氢碳膜(a-C:H)。通过扫描电子显微镜、原子力显微镜观察薄膜表面与断面的形貌,通过傅里叶红外光谱仪表征了碳膜的碳氢键结构,通过纳米压痕仪、划痕仪、摩擦磨损实验评价薄膜的力学及摩擦学性能,通过透射电子显微镜分析磨屑结构,并通过光学显微镜及三维轮廓仪对磨斑及磨痕形貌进行分析。结果类富勒烯结构对薄膜的机械力学性能影响不大,但是对其大载荷下的摩擦学性能有影响。与a-C:H碳膜相比,小载荷下(5 N),FL-C:H碳膜的摩擦系数较高,大载荷下(20 N),FL-C:H碳膜具有较低的摩擦系数(0.03)和磨损率(4.8×10-8 mm~3/(m·N)),并且其摩擦界面形成了类球状纳米结构颗粒。随着载荷的增加,FL-C:H碳膜的摩擦系数和磨损率先降低,后基本不变,在载荷大于15 N时,摩擦界面形成了类球状纳米结构颗粒。结论类球状纳米结构颗粒的形成能降低薄膜的摩擦系数和磨损率,而FL-C:H碳膜比a-C:H碳膜更易在摩擦界面形成类球状纳米结构颗粒。这种类球状纳米结构的形成还依赖于载荷的大小(大载荷时更易形成),因此类富勒烯碳膜在大载荷下更易保持低的摩擦系数及磨损率。     

SrAl2O4基应力发光监测预警涂层的研究进展

采用应力发光材料在目标结构表面构筑功能涂层可对结构损伤进行实时监测预警,不仅提高了设施的安全性,还为检修工作和损伤机理的研究提供了帮助,应用潜力巨大。为促进这类涂层的研发与应用,首先介绍了弹性应力发光材料的发展历程及基本特征,通过对比突出了SrAl₂O₄基材料的综合优势。然后详细分析了SrAl₂O₄基质的晶体结构、缺陷类型对能级分布、电子运动状态以及光的吸收与发射性能的影响,并论述了元素掺杂对发光强度、波段和灵敏度等发光性能的影响。接着介绍了应力发光常用的检测表征方法和基于现象分析形成的应力发光机理。在此基础上,进一步总结归纳了制备应力发光粉末的主要方法以及影响其物相结构、晶体尺寸和发光性能的核心因素,分析了各自的优缺点。详细介绍了制备监测预警涂层的表面技术和工程应用案例,发现该类涂层仍存在敏感度不高、后处理工艺苛刻和界面结合差等问题。最后,从探究应力发光本质、制备实用性更强的预警涂层和制定生产测试标准3个角度提出了一些建议。     

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MoD...