低温沉积Ag-Cu薄膜的耐原子氧和摩擦学性能

采用多弧离子镀在低温(173 K)沉积了Ag-Cu薄膜,通过地面原子氧模拟试验机构考察了薄膜的耐原子氧性能,通过X射线衍射(XRD)、原子力显微镜(AFM)和球-盘摩擦试验机对薄膜结构、耐原子氧性能和摩擦学性能进行了表征,并与室温(300 K)及低温(173 K)沉积Ag薄膜进行了比较研究.结果表明:低温沉积Ag-Cu薄膜由面心立方结构的AgCu合金相和少量Ag或Cu组成,Cu元素合金和低温沉积可细化Ag薄膜的晶畴尺寸、提高其致密性,细密的薄膜结构有利于抑制原子氧对薄膜的攻击,因此低温沉积的Ag-Cu薄膜表现出较好的耐原子氧性能;磨损试验结果表明低温沉积的Ag-Cu薄膜表现出较好的耐磨性,这主要归因于其细密的薄膜结构和较高的膜-基结合强度,此外由于其耐原子氧性能的改善,低温沉积Ag-Cu薄膜在原子氧辐照前后磨损率的增加明显低于低温和室温沉积Ag薄膜.     

油溶性纳米Cu在微动磨损条件下的自修复行为与机理研究

将质量分数为1%的油溶性纳米铜分散于SJ 15W/40汽油机油中并以SJ 15W/40汽油机油为参比油、采用SRV型微动摩擦磨损试验机考察了油溶性纳米铜添加剂的摩擦磨损自修复行为.用表面轮廓仪、显微硬度计、扫描电子显微镜以及X射线光电子能谱仪等对摩擦副磨损表面进行了分析.结果表明,在本试验条件下,与参比油相比,添加油溶性纳米铜的SJ 15W/40汽油机油的摩擦系数和磨损体积损失均有大幅降低,且在达到一定试验时间和载荷后出现磨损负增长,表现出了明显的磨损自修复效应.油溶性纳米Cu能够改善摩擦副的表面磨损状况,使其得到整平和修复,其机理主要为软金属纳米颗粒(纳米Cu颗粒)在摩擦过程中由于物理、化学和电化学等作用而沉积于摩擦表面,形成含有单质铜的自修复沉积膜,从而起到了磨损自修复作用.     

多弧镀及磁过滤阴极弧沉积TiN薄膜的摩擦学性能对比

分别采用多弧离子镀(MAIP)和带有平面"S"形过滤管的磁过滤阴极弧设备(FCAP)在不锈钢基底上制备了2种TiN薄膜;采用往复式球-盘摩擦磨损试验机评价了2种薄膜的摩擦学性能;采用扫描电子显微镜观察和分析了薄膜磨斑表面形貌及其元素面分布.结果表明:采用FCAP技术制备的薄膜表面光滑、缺陷少、普遍具有明显的(111)面择优取向;而采用MAIP技术制备的薄膜表面存在较多大小不一的颗粒和孔洞,且无明显取向.在较低载荷下,采用FCAP薄膜表现出较好的抗磨性能,其磨斑表面存在沉积的TiN磨屑;而采用MAIP制备的薄膜磨斑表面无转移沉积磨屑,摩擦系数较高.     

固-液复合润滑对轴承钢摩擦学性能的影响

为了提高GCr15钢的耐磨性和承载能力,采用低温离子渗硫技术在GCr15钢的表面制备了FeS固体润滑薄膜,在球-盘摩擦磨损试验机上对比研究了在基础油及2种含硫极压抗磨添加剂(ZDDP和SO)润滑条件下GCr15钢渗硫前后的摩擦学性能.利用SEM观察了磨损表面的形貌,利用XPS分析了磨损表面边界润滑膜化合物的价态及元素随深度的变化.研究表明:在摩擦过程中,表面的硫化层会阻碍润滑油中的添加剂与基体之间的作用,当添加剂与基体直接接触时其作用才能发挥.只有当硫化层破坏程度较小时,与添加剂的复合作用效果才较为明显.含硫添加剂与基体之间的反应可以补充硫化层因磨损失去的FeS,体现了显著的复合润滑效果.其中,高活性的硫烯比需要温度催化的ZDDP对硫化层的补充作用更明显.     

四面体无定型无氢非晶碳膜的制备及其摩擦学性能研究

采用磁过滤阴极真空弧系统分别在硅片[Si(100)]、W18Cr4V高速钢和Cr18Ni9不锈钢基体上沉积了一系列sp3键含量较高的四面体无定型无氢非晶碳膜(ta-C),研究了所合成薄膜的结构、硬度、附着强度和摩擦磨损性能,考察了基体和薄膜厚度对薄膜摩擦系数的影响,简要分析了相应ta-C膜的失效机理.结果表明,在高速钢基体上沉积的ta-C膜的显微硬度为76 GPa,结合力Lc值达42 N,具有优良的摩擦学性能,其摩擦系数为0.12,且摩擦系数可以在16 000 r范围内保持稳定.     

干摩擦条件下基体粗糙度对Cr-DLC薄膜摩擦磨损性能的影响

采用磁控溅射/等离子辅助气相沉积方法在不同粗糙度样品表面制备Cr掺杂类金刚石(Cr-DLC)薄膜,研究了干摩擦条件下,基体粗糙度对Cr掺杂类金刚石薄膜摩擦磨损性能的影响.结果表明:在低表面粗糙度样品上体现了Cr掺杂类金刚石薄膜良好的自润滑特性,平均摩擦系数在0.1以下,达到了油润滑条件的摩擦水平,磨损较小,磨损表面薄膜结构完整,未出现明显石墨化转变.在高表面粗糙度样品上,样品的平均摩擦系数提高了3~4倍,磨损剧烈,基体表面磨出了明显的沟槽,与其对摩的Si_3N_4球磨损严重.     

炭纤维和氧化铜增强尼龙1010复合材料的摩擦学性能及磨损机理

以注塑成型法制备了无机填料 Cu O和炭纤维增强尼龙 10 10 (PA10 10 )复合材料 ,采用 MM- 2 0 0型摩擦磨损试验机考察了复合材料的摩擦磨损性能 ,分析了磨损表面和转移膜形貌 .研究结果表明 :Cu O和炭纤维可以显著改善尼龙复合材料的摩擦学性能 ,以 2 0 % CF- 10 % Cu O- PA10 10的耐磨性能和拉伸强度最高 ;在摩擦过程中炭纤维促进 Cu O还原生成单质铜微粒 ,形成具有良好自润滑性能的含铜转移膜 ,对减少摩擦副之间的磨粒磨损和粘着磨损及提高转移膜的结合强度起重要作用     

Mo基固溶体增韧Mo2Ni3Si金属硅化物合金高温滑动磨损性能

以Mo、Ni和Si金属粉末为原料,利用激光熔化沉积技术制备Mo基固溶体(Moss)增韧Mo2Ni3Si金属硅化物耐磨材料,在销-盘式摩擦磨损试验机上评价合金在400～550 ℃范围内的磨损性能,借助扫描电子显微镜观察合金磨损表面及其亚表面形貌.结果表明,Moss增韧Mo2Ni3Si金属硅化物合金在高温滑动条件下表现出反常的磨损率-温度关系,即磨损率随温度的升高而降低,其磨损表面光滑平整,没有显微切削和犁沟等特征,Moss树枝晶在试验温度下发生了轻微氧化.金属硅化物Mo2Ni3Si在磨损过程中起到了抗磨作用,韧性良好的Moss树枝晶有效地抑制了Mo2Ni3Si基体的裂纹扩展和显微剥落.合金在高温滑动条件下的主要磨损机理为软磨粒磨损和Moss相的轻微氧化.     

纳米弹性复合DLC薄膜的制备及其摩擦性能研究

利用磁过滤阴极真空弧沉积系统在硅片及以硅片为基底的2种弹性体材料表面沉积厚度为2.7 nm的DLC膜,采用原子力显微镜和拉曼光谱仪对薄膜的形貌及成分进行分析,用纳米力学测试系统测量薄膜的弹性模量和硬度,用UMT-2型多功能微摩擦磨损试验机考察其摩擦性能.结果表明,以γ-缩水甘油醚氧丙基三甲氧基硅烷(187)为偶联剂的薄膜试样表面比以γ-氨丙基三乙氧基硅烷(APS)为偶联剂的薄膜试样表面更致密且粗糙度更低,薄膜的最上层为DLC膜.在硅表面沉积DLC薄膜可以显著降低其表面的摩擦系数(0.117～0.137),在低载荷条件下,含偶联剂及弹性体的DLC薄膜的摩擦系数低于硅表面沉积DLC的薄膜,且以187为偶联剂的薄膜试样的摩擦性能更佳;在高载荷条件下,硅表面沉积DLC的薄膜具有更优异的摩擦性能.     

碳纤维毡增强铝基复合材料的摩擦磨损性能研究

采用压挤渗透工艺制备了新型碳纤维毡增强铝基复合材料,在MG－2000型高速高温摩擦磨损试验机上考察了其摩擦磨损性质,结果表明：碳纤维毡增强铝基复合材料的摩擦磨损特性明显估于基体合金;复合材料经历由稳定磨损向严重磨损的转化;在稳定磨损阶段,复合材料的磨损表面存在由金属氧化物和碳膜共同构成的复合固体润滑膜,从而有效地改善复合材料的摩擦磨损性能。     

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)     

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.     

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。     

Sound and vorticity interactions: transmission and scattering

We review several aspects of the propagation of sound in vortical flows. We restrict ourselves to isothermal, humidity-free flows at low Mach number M. Since vorticity plays a major role in vortex-flow interactions we focus on vortical flows. We consider two main canonical situations. The first concerns the transmission of sound. We analyze the evolution of acoustic wavefronts as they propagate across a single vortex. The second situation addresses the scattering of sound waves by nonstationary vortices. We study the evolution of the acoustic pressure emitted in the far field, at an angle with the initial direction of propagation. In this geometry one performs direct spectroscopy of the flow vorticity field. In each case, we review theoretical results and compare with experimental measurements and numerical simulations when available. We also briefly report how the following new acoustic techniques have recently been used to study complex or turbulent flows: time-resolved acoustic spectroscopy, speckle interferometry and Lagrangian particle tracking. PACS 43.25, 43.28, 47.32, 67.40     

Flows around two airfoils performing fling and subsequent translation and translation and subsequent clap

The aerodynamic forces and flow structures of two airfoils performing “fling and subsequent translation“ and “translation and subsequent clap“ are studied by numerically solving the Navier-Stokes equations in moving overset grids. These motions are relevant to the flight of very small insects. The Reynolds number, based on the airfoil chord length c and the translation velocity U, is 17. It is shown that: (1) For two airfoils performing fling and subsequent translation, a large lift is generated both in the fling phase and in the early part of the translation phase. During the fling phase,a pair of leading edge vortices of large strength is generated; the generation of the vortex pair in a short period results in a large time rate of change of fluid impulse, which explains the large lift in this period. During the early part of the translation, the two leading edge vortices move with the airfoils;the relative movement of the vortices also results in a large time rate of change of fluid impulse, which explains the large lift in this part of motion. (In the later part of the translation, the vorticity in the vortices is diffused and convected into the wake.) The time averaged lift coefficient is approximately 2.4 times as large as that of a single airfoil performing a similar motion. (2) For two airfoils performing translation and subsequent clap, a large lift is generated in the clap phase. During the clap, a pair of trailing edge vortices of large strength are generated; again, the generation of the vortex pair in a short period (which results in a large time rate of change of fluid impulse) is responsible for the large lift in this period. The time averaged lift coefficient is approximately 1.6 times as large as that of a single airfoil performing a similar motion. (3) When the initial distance between the airfoils (in the case of clap, the final distance between the airfoils) varies from 0.1 to 0.2c, the lift on an airfoil decreases only slightly but the torque decreases greatly. When the distance is about lc， the interference effects between the two airfoils become very small.     

Data-driven modeling and learning in science and engineering

In the past, data in which science and engineering is based, was scarce and frequently obtained by experiments proposed to verify a given hypothesis. Each experiment was able to yield only very limited data. Today, data is abundant and abundantly collected in each single experiment at a very small cost. Data-driven modeling and scientific discovery is a change of paradigm on how many problems, both in science and engineering, are addressed. Some scientific fields have been using artificial intelligence for some time due to the inherent difficulty in obtaining laws and equations to describe some phenomena. However, today data-driven approaches are also flooding fields like mechanics and materials science, where the traditional approach seemed to be highly satisfactory. In this paper we review the application of data-driven modeling and model learning procedures to different fields in science and engineering.     

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.     

Reordering and incomplete preconditioning in serial and parallel adaptive mesh refinement and coarsening flow solutions

The effects of reordering the unknowns on the convergence of incomplete factorization preconditioned Krylov subspace methods are investigated. Of particular interest is the resulting preconditioned iterative solver behavior when adaptive mesh refinement and coarsening (AMR/C) are utilized for serial or distributed parallel simulations. As representative schemes, we consider the familiar reverse Cuthill–McKee and quotient minimum degree algorithms applied with incomplete factorization preconditioners to CG and GMRES solvers. In the parallel distributed case, reordering is applied to local subdomains for block ILU preconditioning, and subdomains are repartitioned dynamically as mesh adaptation proceeds. Numerical studies for representative applications are conducted using the object‐oriented AMR/C software system libMesh linked to the PETSc solver library. Serial tests demonstrate that global unknown reordering and incomplete factorization preconditioning can reduce the number of iterations and improve serial CPU time in AMR/C computations. Parallel experiments indicate that local reordering for subdomain block preconditioning associated with dynamic repartitioning because of AMR/C leads to an overall reduction in processing time. Copyright © 2011 John Wiley & Sons, Ltd.     

Phase transitions and hysteresis in nonlocal and order-parameter models

The paper describes two types of regularization to the basic quasistatic double-well potential problem in one space dimension. One model features a spatially nonlocal term while the other incorporates the use of an order parameter. Some basic existence and regularity results for these modified models are derived and some numerical calculations that show hysteresis and motion of phase boundaries are presented.

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Sommario Il lavoro descrive due tipi di regolarizzazione del problema quasistatico per un potenziale con due minimi in una dimensione. Un modello evidenzia caratteri di non località spaziale, mentre l'altro conduce ad una teoria con parametro d'ordine. Si derivano alcuni risultati di esistenza e regolarità e si presentano alcuni studi numerici che mostrano l'isteresi e il moto delle frontiere tra le fasi.