滚压诱导梯度超细晶铜的润滑微动磨损特性研究

通过滚柱对纯铜表面进行大载荷的多次滚压,使其表层累积不同应变水平的塑性变形,对所形成的约150μm的塑性变形层沿深度方向的晶粒形态和分布进行分析,并对其显微硬度进行测试,表明该工艺在纯铜表层诱导形成了一种梯度超细晶结构;最表层平均晶粒尺寸约为662 nm,并随深度逐渐增至基体晶粒尺寸94μm;梯度超细晶铜(简称梯度铜)最表层硬度较基体硬度提高约45%,并随深度逐渐下降至基体硬度.在SRV IV试验机上对梯度铜和粗晶铜在润滑条件下的微动磨损特性进行对比研究.结果表明:梯度铜摩擦系数先减小后增大,并在大载荷下与粗晶铜趋于一致;梯度铜的主要磨损形式为磨粒磨损,而粗晶铜为磨粒磨损和疲劳剥落,部分区域出现氧化磨损;梯度铜抗微动磨损能力比粗晶铜提高10倍以上.     

YL12铝合金铁离子注入层的摩擦学特性研究

对 YL12铝合金进行了铁离子注入 ,用俄歇电子能谱 (AES)分析了注入层剖面元素分布 ,同时考察了注入层的表面显微硬度、脆性和在干摩擦条件下的摩擦磨损特性 .采用扫描电子显微镜 (SEM)对磨痕表面形貌进行了观察分析 .研究结果表明 :铁离子在注入层中沿剖面呈高斯分布 ;注入层表面显微硬度有所增加 ,摩擦系数显著降低 ;当注入剂量为 7× 10 1 6 Fe / cm2 时 ,注入试样的耐磨性为未注入试样的 3 80 0倍 ;随着铁离子注入剂量的增大试样的表面脆性增加 ,耐磨性降低 ;注入前材料的磨损机制以粘着磨损和磨粒磨损为主 ,注入后磨损机制则以氧化磨损为主     

不同管径氧化钛纳米管层的微动磨损性能

利用阳极氧化法在纯钛表面制备了3组平均内径不同的TiO2纳米管层试样,用扫描电子显微镜、硬度仪和轮廓仪对试样表面形貌、显微硬度、纳米硬度和粗糙度进行测试.在大气环境里,以球/平面接触方式,对摩偶件为超高分子聚乙烯球,采用PLINT高精度液压伺服式微动磨损试验机,分别在4种法向载荷下,对试样进行微动磨损试验.结果表明:随法向载荷的增加,同一摩擦副的摩擦系数降低;TiO2纳米管层的存在降低了钛与UHMWPE之间的摩擦系数,在不同载荷下纳米管层表面的摩擦系数均随管径的增大而增大,但低于无纳米管层的对照组;与UHMWPE对摩,TiO2纳米管层有很好的承载、抗剥离和耐磨性能;摩擦副的主要磨损机理为磨粒磨损、UHMWPE塑变导致的表层材料损失.     

电沉积纳米晶Ni-Co-Fe-P合金镀层的组织结构与摩擦磨损性能

用脉冲电沉积方法制备了纳米晶N i-Co-Fe-P合金镀层.采用X射线衍射（XRD）,透射电镜（TEM）,扫描电镜（SEM）,能谱分析（EDS）等方法研究了合金镀层的微观组织结构和成份.采用显微硬度计和摩擦磨损试验机测试合金镀层的显微硬度和摩擦磨损性能.结果表明：纳米晶N i-40.41%Co-6.16%Fe-1.63%P合金镀层的晶粒尺寸为8.3 nm,显微硬度和耐磨性明显高于不含P的N i-Co-Fe镀层;适当温度退火可以提高镀层的硬度及耐磨性;镀层的耐磨性与其硬度成正相关,且随着硬度的提高,镀层的磨损机理由磨粒磨损和黏着磨损共同作用转变为磨粒磨损主导.     

电沉积方式对纳米晶钴镀层的结构和摩擦学性能影响研究

采用不同电沉积方式制备了不同结构和晶粒尺寸的纳米晶钴(Co)镀层.采用扫描电镜和X-射线衍射仪分别分析了镀层表面形貌、晶相结构与晶粒尺寸.采用MV-2T显微硬度计测试镀层的硬度.最后采用UMT-3M多功能摩擦磨损试验机对镀层的摩擦和磨损性能进行了评价,并用扫描电镜对其磨损表面进行了观察分析.结果表明:电沉积方式对制备的纳米Co镀层的晶相结构、晶粒尺寸、镀层形貌和摩擦磨损性能影响显著;采用双脉冲制备的纳米Co镀层具有最小的晶粒尺寸、最高的硬度及较好的耐磨性能;采用单双脉冲混合电镀制备的纳米Co镀层表面针孔孔洞直径最小,结构最致密,耐磨性能最好.这些研究结果说明可通过优化电沉积方式来提高镀层的结构致密性,改善其硬度和耐磨性能.     

等离子堆焊Stellite合金高温摩擦磨损特性研究

采用等离子堆焊技术在气门用钢基体上制备了Stellite 1和Stellite F合金堆焊层,对堆焊层的金相组织、物相组成和硬度等进行了研究,在MMU-10G高温端面摩擦磨损试验机上考察了不同温度条件对2种堆焊层摩擦磨损性能的影响,并分析了堆焊层的磨损机理.结果表明:高温条件下,随着温度的上升,2种合金堆焊层的摩擦系数增大,磨损体积减小;温度为400℃时,Stellite 1和Stellite F合金堆焊层分别产生了大量的疲劳裂纹和宽大的犁沟,磨损较为剧烈;温度为500和600℃时,2种合金堆焊层磨损机制相似,主要磨损机制分别为疲劳剥落和磨粒磨损;氧化膜的快速形成以及上试样硬度的下降减小了磨损,磨痕中心区域变窄,磨痕边缘的磨屑不断堆积并被碾压产生了严重的黏着磨损,导致摩擦系数增加.     

高性能渗氮钢微动磨损性能研究

采用等离子渗氮技术在1种高性能钢材表面进行了等离子渗氮.对处理后的试样进行了金相组织分析,测试了渗氮层的显微硬度,然后在SRV IV试验机上在常温条件下考察了渗氮钢微动摩擦磨损性能.结果表明:经等离子渗氮后试样表面形成了硬度较高的渗氮层,渗层硬度最大值是基体硬度的2.8倍;与未渗氮样相比,干摩擦时表面摩擦系数、磨损体积降低最大幅度分别约为28%、80%,渗氮样的主要磨损机理为氧化磨损和疲劳剥落;油润滑时表面摩擦系数、磨损体积降低最大幅度分别约为37%、97%,渗氮样主要磨损机理为磨粒磨损和裂纹扩展引起的细块状剥落;渗氮处理后的试样表面抗微动磨损性能更加优异.     

纳米碳管/铝基复合材料的制备及摩擦磨损性能研究

利用粉末冶金法制备纳米碳管/铝基复合材料,研究不同纳米碳管含量对复合材料硬度和稳态摩擦磨损行为的影响,采用扫描电子显微镜观察复合材料的磨损表面形貌,并对其磨损机制进行探讨.结果表明:随着纳米碳管质量分数的增加,复合材料的硬度呈现先增大而后减小的趋势,含质量分数为2%的纳米碳管复合材料硬度比铝增加约80%;复合材料的摩擦系数逐渐降低,磨损率先减小而后增大;含质量分数为1%的纳米碳管复合材料磨损机制为磨粒磨损和粘着磨损,而含质量分数为2%的纳米碳管复合材料以剥层磨损和疲劳磨损为主.     

氮合金化堆焊合金往复式摩擦磨损行为的研究

在马氏体不锈钢中引入氮，通过铌、钛固氮制备氮合金化堆焊合金. 利用往复式摩擦磨损试验机测试加氮和未加氮两种堆焊合金在不同载荷(5、10和15 N)下的摩擦磨损性能，研究了其摩擦磨损行为. 结果表明:在摩擦磨损过程中，堆焊合金表面承受周期性载荷，摩擦表面出现明显的切削痕和塑性变形，其磨损机制以磨粒磨损和表面疲劳磨损为主. 氮合金化堆焊合金中，碳氮化物沿马氏体基体、晶界弥散析出，起到了明显的细晶强化和弥散强化作用，增强了基体的塑性变形抗力以及抵御磨粒磨损的能力，使磨损表面切削痕数量更少、深度更浅，抗疲劳剥落现象得到明显改善.      

含内生硬质碳化物颗粒的金属堆焊层的抗磨性能及磨损机理

利用钛铁(Fe-Ti)、钒铁(Fe-V)、石墨和金红石等组分的电弧冶金反应合成了含TiC和VC硬质碳化物颗粒的金属堆焊层；采用MLD-10型动载荷摩擦磨损试验机考察了金属堆焊层的抗磨性能，探讨了其磨损机理．采用X射线衍射仪和扫描电子显微镜分析了堆焊层的相组成＼微结构及磨损表面形貌．结果表明：含硬质碳化物颗粒的金属堆焊层具有良好的耐磨粒磨损性能，其单位面积磨损质量损失仅为EDZCr-C-15焊条相应金属堆焊层的约1／9；所制备的金属堆焊层基体组织为低碳马氏体，内生硬质碳化物颗粒弥散分布于基体组织中；硬质碳化物颗粒同低碳马氏体基体表现出良好的韧性和硬度复合效果，从而有利于显著提高金属堆焊层的抗磨性能．     

Combustion of a Powder Layer of Methane Hydrate: The Influence of Layer Height and Air Velocity Above the Layer

The paper studies the dissociation and combustion of a layer of methane hydrate powder at a forced air flow over the upper surface of the layer (the air velocity is directed parallel to the upper surface of the layer). The influence of the layer thickness and air velocity on the combustion of gas hydrate is investigated. The calculated curves for the effect of the heat transfer coefficient, external convection and vapor concentration on the combustion temperature are obtained. The layer thickness and the air velocity significantly affect the dissociation rate of methane hydrate.

     

Marangoni Mixed Convection Boundary Layer Flow

The paper deals with a steady coupled dissipative layer, called Marangoni mixed convection boundary layer, which can be formed along the interface of two immiscible fluids, in surface driven flows. The mixed convection boundary layer is generated when besides the Marangoni effects there are also buoyancy effects due to gravity and external pressure gradient effects. We shall use a model proposed by Golia and Viviani (L’ Aerotecnica missili e Spazio 64 (1985) 29–35, Meccanica 21 (1986) 200–204) wherein the Marangoni coupling condition has been included into the boundary conditions at the interface. The similarity equations are first determined, and the pertinent equations are solved numerically for some values of the governing parameters and the features of the flow and temperature fields as well as the interface velocity and heat transfer at the interface are analysed and discussed.     

Equations of an Elastic Anisotropic Layer

Differential equations of an elastic orthotropic layer are constructed on the basis of expansion of the solutions of the elasticity theory in terms of the Legendre polynomials. The order of the system of differential equations is independent of the form of the boundary conditions on the layer surfaces, which allows a correct formulation of conditions on contact surfaces.     

Boundary Layer Solutions in Elastic Solids

Circumferential shear deformation in an annular domain is studied for a large class of incompressible isotropic elastic materials. It is demonstrated that large strains are confined in a region adjacent to a boundary, in analogy to the boundary layer phenomenon in fluid mechanics. The size of this region is quantified. An approximate solution technique for the deformation of nonlinear elastic solids, proposed by Rajagopal [7], is further studied. In this solution, akin to the boundary layer approximation in classical fluid mechanics, the full nonlinear problem is solved in a relatively small region of large strain, while the linearized problem is solved in the remaining region. Error estimates for the approximate solution are obtained.     

Exchange of Chemical Species between the Atmospheric Boundary Layer and the Reservoir Layer: An Analytical Interpretation

The exchange of chemical species between the atmospheric boundary layer and the reservoir layer is investigated by means of an analytical solution of the conservation equation of a decaying chemical species. The exchange mechanism is governed by two parameters: the Damköhler number (the ratio of the turbulence time scale to the chemical time scale) and the ratio of a concentration scale in the atmospheric boundary layer to the concentration in the reservoir layer. Depending on the value of these two parameters, the exchange flux between the two layers can vary in sign and by several orders of magnitude. The study demonstrates to what extent chemical transformation determines the transfer of chemical species between the atmospheric boundary layer and the reservoir layer.     

A Circular Indenter on a Piezoelectric Layer

This paper investigates a piezoelectric layer with a rigid indenter on its surface. Exact solution is given for a piezoelectric medium whose thickness is considerably larger than the diameter of the indenter. Different electrical boundary conditions that employ conducting or insulating indenters are presented. Effect of the permittivity of air (which surrounds the piezoelectric medium) is considered and is found to be negligible. Expressions for the singular mechanical and electric fields near the indenter front are established. Those expressions are useful for investigating the possible failure behavior of piezoelectric material near the indenter front. In addition, a numerical solution technique for an indentured piezoelectric layer of finite thickness is also given.     

壁湍流边界层奇异标度律的实验研究

采用热线风速仪对平板湍流边界层的流向速度进行测量,用速度结构函数研究不同尺度结构标度律的变化规律,结果显示小尺度区的概率密度曲线尾部明显偏离高斯型,说明高幅值间歇性事件占的份额较多;惯性子区的曲线向高斯型靠近,间歇性事件所占份额减少;大尺度结构的曲线趋于高斯型,间歇性事件所占份额最小。在耗散区、惯性子区和较大的尺度结构区存在大小不同的绝对标度指数,越靠近壁面这些区域的标度指数均越偏离p/3而逐渐变小。绝对标度指数与边界层位置有关,在缓冲层各阶标度指数与线性标度律偏差很大,显示较强的奇异性,当过渡到对数层及外区,标度指数逐渐增大,接近均匀各向同性湍流的状态。缓冲层、对数层及外区具有各异的绝对标度指数增长率,与各层的不同湍流结构特征和运动形式有关。     

大气边界层的风洞模拟

本文通过比较大气边界层与不同比尺的模型实验，研究了风洞模型实验中的比尺效应。结果表明，大气边界层粗糙高度的比尺应当和边界层厚度比尺相等。边界层厚度的比尺在２００～４００之间时可以得到最好的速度分布的相似性，表面压强分布主要依赖于边界层比尺而与建筑物几何比尺关系不大。如果正确选择了粗糙高度比尺，扩散系数比尺和边界层厚度比尺相同。