TC4(Ti-6Al-4V)氧化膜在生理介质中的摩擦电化学行为

应用阳极氧化和微弧氧化的方法分别制作了TC4(Ti-6Al-4V)表面氧化膜,分别在0.9% NaCl溶液和模拟人工体液中以PTFE盘作摩擦偶件,在圆平动盘销式摩擦磨损试验机进行摩擦电化学试验,获得了对应的摩擦系数,采用三电极体系得到摩擦电化学特性曲线.结果表明,静态时微弧氧化膜耐蚀性比阳极氧化膜提高了近2个数量级;与基体相比,TC4的阳极氧化膜的耐蚀性增强,摩擦系数降低,处理电压越高,摩擦系数越小;虽然TC4的微弧氧化膜的耐腐蚀性能均较阳极氧化膜有大幅度提高,但摩擦系数均较未处理的TC4的摩擦系数大,其中处理时间为20min的微弧氧化膜表现出良好的耐蚀和摩擦性能,通过对磨损试件的SEM形貌对比解释了微弧氧化膜摩擦系数较大的原因,这与膜层表面粗糙度和微孔孔径大小有关.     

TC4合金微弧氧化膜的摩擦磨损性能及其失效机理研究

采用微弧氧化(PEO)技术在TC4合金(Ti6Al4V钛合金)表面制备了微弧氧化耐磨陶瓷膜层. 利用扫描电子显微镜(SEM)、能谱仪(EDS)、X射线衍射仪(XRD)和摩擦试验机分析测试了微弧氧化膜的结构与组成，考察了膜层在干摩擦和油润滑条件下的摩擦磨损性能及其磨损失效机理. 结果表明:基底材料的氧化和电解液化合物的沉积均对微弧氧化膜层的生长起重要作用；微弧氧化有效提高了材料的耐磨性，降低了材料在油润滑条件下的摩擦系数；在干摩擦条件下，摩擦力较大，剪切应力是导致膜层失效的主要因素，在油润滑环境中，压应力是导致膜层失效的主要因素；对微弧氧化膜层进行有效润滑可以极大地提高膜层的使用寿命.      

Ti6A14V表面微弧氧化陶瓷涂层的结构和摩擦学特性

采用交流微弧氧化法，在Na2SiO3-(NaPO3)6-Na3MoO4溶液中制备了Ti6A14V表面氧化物陶瓷涂层，用X射线衍射仪、扫描电子显微镜和球-盘摩擦磨损试验机研究了涂层的结构、形貌及摩擦学性能，用纳米压痕仪测定了涂层致密层的硬度，用扫描电子显微镜观察涂层磨损表面形貌，用能谱仪分析涂层磨屑的元素组成．结果表明：厚约20pm的涂层致密均匀，主要由锐钛矿和金红石相氧化钛组成；涂层致密层的硬度约为13．5GPa；在0．5N低载荷和摩擦循环次数小于2000次条件下，涂层同GCrl5钢对摩时的摩擦系数仅为0．18～0．20，较基底Ti6A14V与其对摩的摩擦系数低得多．摩擦过程中较软的GCr15钢球材料向涂层表面转移，涂层的磨损机制主要是轻微磨粒磨损与粘着磨损．     

碳钢表面微弧氧化膜的制备及摩擦磨损性能研究

在碳钢表面利用微弧氧化技术分别在以铝酸盐和硅酸盐为主的电解液体系中制备了氧化膜.用扫描电子显微镜(SEM)、能谱仪(EDS)和X射线衍射仪(XRD)研究了两种氧化膜的结构、元素含量及分布和相组成;用往复摩擦试验机评价了氧化膜的摩擦磨损性能,并对膜层和对偶表面的磨痕进行了表征.结果表明:铝酸盐体系中制得的微弧氧化膜主要由Fe3O4和铁铝尖晶石(Fe Al2O4)组成,而硅酸盐体系制得的微弧氧化膜成膜元素为Fe、Si和O,并且以非晶态存在.干摩擦条件下,铝酸盐体系中制备的微弧氧化膜具有比硅酸盐体系中制备的微弧氧化膜更低的摩擦系数和磨损率,这是由于铝酸盐中制备的氧化膜含有的Fe3O4在摩擦过程中向对偶发生了一定程度的转移,起到了减摩抗磨的作用.     

扩散铝涂层对TiAl合金摩擦磨损性能的影响

利用多弧离子镀技术在TiAl合金表面制备镀铝层,分别进行720℃×2 h和840℃×2 h高温扩散处理.采用SEM、EDS和XRD分析了膜层的显微组织及相组成,并测试了显微硬度和耐磨性.结果表明:扩散层由氧化表层和扩散内层组成,不含纯铝相;与基体相比,扩散层的表面显微硬度和耐磨性显著提高,其中840℃扩散层的耐磨性优于720℃的扩散层.     

钛合金表面Ti-Al合金扩散层的摩擦性能研究

利用双层辉光离子渗金属技术,以纯铝作为源极,氩气为工作气体,利用不等电位空心阴极效应在钛合金(Ti6Al4V)表面渗铝,形成均匀致密的钛铝合金扩散层,采用WTM-1型球-盘摩擦磨损试验机对钛合金表面钛铝合金扩散层的摩擦性能进行研究,用显微硬度仪测量渗层的显微硬度,并用扫描电子显微镜和X射线衍射仪观察分析钛铝合金扩散层的截面形貌和相结构.结果表明:在Ti6Al4V合金基材表面形成厚20 μm的钛铝合金扩散层,其表面显微硬度达810HV;钛铝合金扩散层主要由金属间化合物Ti3Al和TiAl组成;钛铝合金扩散层可以显著提高钛合金表面的摩擦性能,摩擦系数从0.35左右降至0.15,抗磨损性能大幅提高.     

油溶性有机钼添加剂作用下微弧氧化改性TC4钛合金的摩擦学性能

借助微弧氧化技术在TC4钛合金表面构筑了高硬度氧化物薄膜,利用X射线衍射仪(XRD),扫描电子显微镜(SEM)及拉曼光谱等手段对膜层结构进行了分析,考察了二烷基二硫代氨基甲酸钼(MoDTC)作为聚α烯烃PAO6润滑添加剂对微弧氧化薄膜的摩擦学性能的影响. 结果表明:经过微弧氧化处理后得到的钛合金试样展现了优异的减摩抗磨性能,与未处理的TC4样品相比,在含质量分数为2% MoDTC的PAO6油润滑下,摩擦系数降低了87.4%,磨损率下降了3个数量级. 这主要是因为经微弧氧化处理后,TC4钛合金表面形成的TiO₂薄膜具有较高硬度与耐磨性,同时促进了MoDTC添加剂在边界润滑条件下的摩擦化学反应,在接触区表面生成含有MoS₂的润滑层.      

工作电压对N36锆合金表面微弧氧化涂层磨蚀性能的影响

通过微弧氧化(MAO)设备在锆(Zr)合金表面制备氧化陶瓷涂层. 研究工作电压对Zr合金表面MAO涂层形貌、硬度、粗糙度、元素分布和相结构的影响. 分析工作电压对Zr合金表面MAO涂层腐蚀和磨蚀性能的影响. 结果表明:MAO涂层表面具有典型的多孔和火山熔融特征,主要由m-ZrO₂和t-ZrO₂相组成. MAO涂层的粗糙度比基体高,且在电压为340 V时的粗糙度最高,达到1.36 μm. MAO涂层可分为内层致密层和外层多孔层,涂层厚度随着工作电压的增加而增加,厚度为5~9 μm. 电压为260 V的MAO涂层的结合强度最高,达到44.3 N. MAO涂层相比较于基体具有更好的耐腐蚀性能,电压为260 V的MAO涂层具有最高的自腐蚀电位(?0.205 V)和最低的腐蚀电流密度(6.24×10?9 A/cm2). 这是因为电压为260 V的MAO涂层具有最致密的结构,而内层致密层可以阻碍腐蚀液进入基体. MAO涂层的主要磨损机理为磨粒磨损和氧化磨损. 工作电压为260 V的MAO涂层的磨损率仅为Zr合金基体的1/4.      

Ti-46Al-2Cr-2Nb和Ti6Al4V合金的干摩擦学性能对比研究

本文以商业Ti-6Al-4V合金为参照,考察了Ti-46Al-2Cr-2Nb(原子比)金属间化合物在不同载荷和速率下的干摩擦学行为,结果表明:Ti-46Al-2Cr-2Nb和Ti6Al4V合金的摩擦系数几乎相同,而Ti-46Al-2Cr-2Nb金属间化合物比Ti-6Al-4V具有更好的抗磨性;Ti-46Al-2Cr-2Nb和Ti6Al4V合金的磨损率均随载荷的增加而增加,Ti-46Al-2Cr-2Nb合金磨损率随滑动速率增加而增加,Ti-6Al-4V合金磨损率却随滑动速率增加呈下降直至稳定的趋势;Ti-46Al-2Cr-2Nb合金的磨损机制主要为疲劳磨损,Ti-6Al-4V合金的磨损机制为塑性变形,犁沟和剥落.     

网纹型表面微结构对Ti-6Al-4V水润滑摩擦学特性的影响

研究了Ti-6Al-4V合金表面网纹型微结构与Si3N4小球对摩时的水润滑摩擦学性能.利用电火花加工技术在Ti-6Al-4V合金表面加工出不同尺寸的网纹结构,运用正交试验设计方法分析了网纹宽度、深度、间宽比和网纹角度对Ti-6Al-4V合金水润滑摩擦学性能的影响.结果表明:具有合适几何参数的网纹结构能够降低摩擦副在水润滑条件下的摩擦系数和磨损量.当网纹角度在45°时,摩擦副的摩擦系数和磨损量能同时降低.网纹宽度对稳态摩擦系数的影响最大,而网纹深度和夹角对摩擦副材料的磨损影响最大.     

Electrogas- and electrohydrodynamic control of gas and liquid jets and flows

The physical and mathematical principles of the method of electrogas-and electrohydrodynamic conversion of electrical signals to pneumatic (hydraulic) signals and vice versa for control of gas and liquid jets and flows in electropneumohydraulic systems are considered. St. Petersburg State Technical University, St. Petersburg 195251. Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 41, No. 2, pp. 25–31, March–April, 2000.     

Fatigue and static strength of notched and unnotched aluminum-alloy and steel specimens

This paper describes a method of presentation of fatigue data on three commonly used aircraft materials, 2024-T3 and 7075-T6 aluminum alloys and normalized SAE 4130 steel, such that variations in fatigue strength with stress-concentration factor can be shown. Comparisons of the fatigue strengths of 2024-T3 and 7075-T6 aluminum are made for the most useful range of stress-concentration factors. Static-strength results of notched and unnotched specimens of the three materials are presented to show how the strength varies with some parameters of the stress concentration. Comparison of the data with one theory for the strength of cracked specimens was made.     

STICTION AND ANTI—STICTION IN MEMS AND NEMS

Stiction in microelectromechanical systems (MEMS) has been a major failure mode ever since the advent of surface micromachining in the 80s of the last century due to large surfacearea-to-volume ratio. Even now when solutions to this problem are emerging, such as self-assembled monolayer (SAM) and other measures, stiction remains one of the most catastrophic failure modes in MEMS. A review is presented in this paper on stiction and anti-stiction in MEMS and nanoelectromechanical systems (NEMS). First, some new experimental observations of stiction in radio frequency (RF) MEMS switch and micromachined accelerometers are presented. Second, some criteria for stiction of microstructures in MEMS and NEMS due to surface forces (such as capillary, electrostatic, van der Waals, Casimir forces, etc.) are reviewed. The influence of surface roughness and environmental conditions (relative humidity and temperature) on stiction are also discussed. As hydrophobic films, the self-assembled monolayers (SAMs) turn out able to prevent release-related stiction effectively. The anti-stiction of SAMs in MEMS is reviewed in the last part. The project supported by the Distinguished Young Scholar Fund of NSFC (10225209), key project from the Chinese Academy of Sciences (KJCX2-SW-L2) and National “973” Project (G1999033103)     

水和水蒸汽热力学物性参数及导数的计算与应用

本文针对现代换热设备设计、两相流动与传热研究的需要,介绍了可供科研使用的水和水蒸汽物性计算方法,完善了计算程序。根据超临界锅炉设计中的超临界水的物性计算,两相流研究和换热设备动态特性研究中对物性导数计算的需要,提供了两个算例,并进行了定性分析。     

Fracture and stability of materials and structural members with cracks: approaches and results

A new alternative approach to fracture problems for materials and structural elements with cracks is set out. It is based on the mechanism of local instability near defects. The approach is used to study the fracture of materials compressed along interacting cracks and the fracture of thin structural members with cracks under tension with allowance for local buckling.__________Translated from Prikladnaya Mekhanika, Vol. 40, No. 12, pp. 18–64, December 2004.     

Fundamental properties of elasto-plastic matrix and existence and uniqueness of elasto-plastic stress and displacement

Based on the assumption that the yield criterionF(,)=0 is a differentiable surface in stress space and by starting from a specially defined real Euclidean space, the fundamental properties of the elasto-plastic matrix in the incremental theory of plasticity is discussed in detail. By using these results, a convex analysis is made to prove the existence and uniqueness of 1) the distribution of incremental elasto-plastic stress for work-hardening materrials; 2) the displacement distribution for work-hardening materials. Material isotropy is assumed in all discussions of relevant problems.     

Drawing and extruding: Theoretical and approximate formulas

Summary The problem of drawing of wires and of strips has been treated in several studies; among these the studies of Sachs seem essential. However, the results deduced according to similar theories are not always in accordance with the experimental results: reduction of area or of thickness are in fact usually smaller than those resulting from the theory. This is in dependance of the fact that Sachs has adopted the Limiting Condition of Yielding by v. Mises, according to which the limit values of stress in traction and compression are equal. More recently other AA. (Alberti, Noto La Diega, Bugini), admitting the Limiting Condition of Yielding by A. (or of the Paraboloid of Revolution) of which we have treated in one of our previous works, attain results tallying with the experience. In the present study the above said subjects are treated as to evidence their unitarian signifiance and clarify their several aspects. The approximate formulas proposed by A. result of easy and quick application. In the same manner are treated other problems, among which the problem of the extrusion (Bagarello, Ammendola).

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Sommario Il problema della trafilatura dei fili metallici e delle strisce di lamiera è stato trattato in diverse Memorie, fra le quali fondamentali sono quelle del Sachs. I risultati dedotti in base a tali studi non sempre però concordano con le risultanze sperimentali: i rapporti di riduzione delle aree o degli spessori sono infatti di norma inferiori a quelli che risultano da tali teorie. Ciò dipende dal fatto che il Sachs ha posto a base dei suoi studi la Condizione di Plastificazione del v. Mises secondo la quale i limiti di resistenza del materiale che si considera alla trazione e alla compressione semplice sono uguali. Più recentemente altri AA. (Alberti, Noto La Diega, Bugini), adottando la Condizione di Plastificazione dell' A. (o del Paraboloide di Rivoluzione), del quale abbiamo trattato in un precedente lavoro, pervengono a risultati più attinenti alla practica. Col presente studio gli argomenti vengono trattati mettendone in evidenza il significato unitario e chiarendone i vari aspetti. Le formule approssimate proposte dall' A. risultano di facile e immediata applicazione. In maniera analoga vengono trattati altri problemi, fra i quali quello dell'estrusione (Bagarello, Ammendola).