脉冲频率对纯钛微弧氧化膜生长特性的影响

在Na₂CO₃-Na₂SiO₃电解液中, 利用微弧氧化技术在纯钛试样表面制备了氧化膜, 并研究了脉冲频率(500～8000Hz)对膜层生长、相组成及表面形貌的影响. 结果表明: 当脉冲频率<2000Hz时, 膜层的生长速率随频率增加迅速减小, 当>4000Hz时, 其生长速率几乎和频率无关. 微弧氧化膜主要由锐钛矿和金红石相TiO₂及少量不饱和氧化物TiO_2-x(0.022的相对含量与频率无关, 而TiO_2-x随频率的增加而逐渐减少. 氧化膜表面多孔, 随着频率的增加, 膜表面的粗糙度和微孔尺寸逐渐减小, 而微孔的密度逐渐增加.     

电参数对Ti6Al4V合金微弧氧化陶瓷膜结构特性的影响

采用交流微弧氧化法于Na₂SiO₃-KOH-(NaPO₃)₆。溶液中在Ti6A14V表面形成了氧化物陶瓷膜.研究了微弧氧化电压与频率对陶瓷膜的生长速率、组织形貌和相组成的影响.结果表明:随电压的升高或频率的减小,膜层的生长速率增加,膜层的表面质量变得粗糙.相对致密均匀的膜层主要由TiO₂(锐钛矿相及金红石相)相组成,电压与频率电参数影响膜层的相组成,随电压的升高和频率的减小,膜层中锐钛矿相TiO₂的相对含量减小,金红石相TiO₂的相对含量增加,并成为主晶相.     

镁合金微弧阳极氧化膜的特性

采用扫描电镜(SEM)、X射线衍射(XRD)等方法初步研究了镁合金微弧氧化膜的成分、相组成及其形貌特征.结果表明,在微弧氧化处理过程中,镁合金基体中的合金元素Al向表面扩散进入氧化膜层,微弧氧化处理液组分中的元素也进入了氧化膜层.氧化膜主要由MgO、Mg2SiO4、MgAl2O4和不定形相组成.在微孤氧化过程中,氧化膜中首先产生的物相为立方结构的MgO,随着氧化时间的延长,氧化膜中出现晶态的MgAl2O4及Mg2SiO4.     

镁合金无铬微弧氧化新工艺

利用正交试验对MB2镁合金无铬、磷、镁微弧氧化成膜工艺进行了研究,同时利用表面分析技术,分析了氧化膜层的显微硬度、截面形貌和相结构,采用动电位扫描法考察了氧化膜的耐腐蚀性能.研究的最佳工艺条件为:30 g/L KOH,45g/L Al(OH)3,2 g/L K2SiO3,2g/L添加剂M,电流密度65 mA/cm2,温度45℃.该微弧氧化新工艺能在镁合金上形成银灰色的氧化膜层,其显微硬度值及耐腐蚀性远优于传统含铬工艺DOW17所形成的膜层;微弧氧化膜主要由MgO,MgAl2O4,Al2O3组成,具有多孔结构,孔径较为均匀,分为内外两层,外层为疏松层,内层为与基体结合牢固的致密层;在成膜过程中,电解液的铝盐浓度和微弧氧化电流密度是影响性能的主要因素.     

镁合金表面微弧氧化-SiO2复合膜层的微观结构和耐蚀性

采用有机醇盐水解法制备SiO2溶胶,用浸溃-提拉制膜技术在AZ31B镁合金微弧氧化陶瓷层表面制备SiO2膜层,研究了镁合金表面微弧氧化-SiO2复合膜层的微观结构和耐蚀性.结果表明:SiO2溶胶进入微弧氧化陶瓷层表面的微孔并形成了SiO2膜层;由微弧氧化陶瓷层和SiO2膜层组成的复合膜层的腐蚀电位比单一陶瓷层明显提高,...     

钛合金微弧氧化陶瓷膜微观特性的分析

微弧氧化膜存在微米量级宏孔,这些宏孔对氧化膜特征的研究非常重要.研究了微弧氧化中电流密度对微弧氧化膜的生长速率、结构形貌及相组成的影响,并对氧化膜进行了离子束抛光处理,分析了氧化膜和微孔的组织结构.研究表明:电源频率固定为1 500 Hz/5 μs和氧化膜厚为10 μm时,随着氧化电流密度的增大,氧化膜的生成速度和孔径都随之增大,但同一膜厚的氧化层组成成分金红石型TiO2和锐钛矿型TiO2的相对含量无明显变化;离子束抛光后的氧化膜膜层外疏内密,放电通道内表面更是淀积了电解液溶质、氧化膜颗粒及基材等多种物质的纳米微颗粒.     

电流密度对铝合金微弧氧化膜的生长及结合力的影响

为了进一步探讨微弧氧化主要参数电流密度对铝合金微弧氧化膜的影响机理,先用微弧氧化技术在LY12硬铝合金上获得陶瓷层,然后考察电流密度对陶瓷膜厚度及其与基体结合强度的影响,再利用扫描电镜(SEM)、X射线衍射(XRD)、光电子能谱(XPS)分析了氧化膜的形貌和组织结构,通过划痕试验和冲击试验研究了氧化膜与基体的结合力.结果表明,随着电流密度的增大,陶瓷氧化膜及其致密层的增长速度均加快,但有一个极限值,氧化膜的临界载荷降低,致密层所占比例也逐渐降低.XPS谱图证明,微弧氧化膜表面疏松层主要由γ-Al2O3,α-Al2O3和Al-Si-O相组成,致密层由α-Al2O3和γ-Al2O3组成.铝合金表面生成氧化膜后,随着膜厚度的增加,冲击韧性逐渐减低,基体断裂后,氧化膜没有发生剥落,表面出现大量微裂纹.     

6061铝合金微弧氧化陶瓷膜的生长动力学及性能分析

研究了6061铝合金微弧氧化陶瓷膜的生长规律,分析不同膜厚度下膜层截面组织、成分和相组成,并测量了氧化膜显微硬度分布和电化学腐蚀特性.氧化膜生长分为3个阶段,随着氧化时间的延长,膜层由向外生长逐渐过渡到向内生长,其表面粗糙度线形增加.氧化膜由α-Al2O3、γ-Al2O3和SiO2非晶相构成,SiO2相主要分布在外部疏松层里.显微硬度极大值随膜厚增加而增大,硬度值同α-Al2O3的相对含量密切相关.6061铝合金经过微弧氧化处理后抗腐蚀能力得到很大提高.     

电流密度对镁合金微弧氧化膜结构和性能的影响

电流密度是影响微弧氧化膜层结构和性能的主要因素之一.采用测厚仪、扫描电镜(SEM)、电化学测试等手段研究了AM60B镁合金在不同电流密度下硅酸盐溶液中微弧氧化膜层的结构和耐蚀性能.结果表明,随电流密度的增大,氧化膜厚度呈线性增加;氧化膜的表面微孔数目减少,微裂纹扩展程度增大.电化学腐蚀测试结果显示,电流密度9.0 A/dm2下生成的氧化膜耐蚀性最好,主要与膜层较致密的微观结构有关.     

镁合金微弧氧化膜相组成及结构分析

为了解镁合金微弧氧化膜的耐蚀性能,研究了其截面不同位置的组织结构及元素分布.通过扫描电镜(SEM)、X射线衍射(XRD)、能谱(EDS)等测试手段,对镁合金微弧氧化膜层的形貌、结构、相组成及元素分布的特点进行了系统分析.结果表明:膜层表面分布着大量均匀的放电微孔;截面致密层厚度占膜层总厚度的60%以上;XRD图谱显示陶瓷层主要由Mg2SiO4和MgO组成;由电能谱面分析可知过渡层n(Mgo):n(Mg2SiO4)=5:1,致密层n(Mgo):n(Mg2SiO4)=1:1;线性扫描测试结果显示从基体到膜层外表面,Mg元素的含量逐渐降低,O与Si元素的分布相似,均呈先增大后减小的趋势,P含量则基本保持不变.     

Estimation of Parameters of Universal Distribution of Moments of Failure of Products

A method is proposed for estimating the parameters of a mixture of exponential and Weibull distributions for which the accuracy of preliminary estimates obtained by graphical analysis is refined in accordance with the criterion of maximum likelihood. The efficiency of the proposed method is supported by the results of statistical modeling.     

Evaluation of optical properties of highly scattering media by moments of distributions of times of flight of photons

A novel method for the determination of the optical properties of tissue from time-domain measurements is presented. The data analysis is based on the evaluation of the first moment and the second centralized moment, i.e., the mean time of flight and the variance of the measured distribution of times of flight (DTOF) of photons injected by short (picosecond) laser pulses. Analytical expressions are derived for calculation of absorption and of reduced scattering coefficients from these moments by application of diffusion theory for infinite and semi-infinite homogeneous media. The proposed method was tested on experimental data obtained with phantoms, and results for absorption and reduced scattering coefficients obtained by the proposed method are compared with those obtained by fitting of the same data with analytical solutions of the diffusion equation. Furthermore, the accuracy of the moment analysis was investigated for a range of integration limits of the DTOF. The moment analysis may serve as a comparatively fast method for evaluating optical properties with sufficient accuracy and can be used, e.g., for on-line monitoring of optical properties of biological tissue.     

Estimation of potentialities of methods of summation of direct measurement errors

Conventional methods for summation of direct measurement errors are considered. Conditions under which these methods provide consistent results are stated. It is proposed to utilize for characteristic of the total error, its interval estimator or the half-sum of the value obtained by adding up its arithmetic and geometric random errors.Translated from Izmeritel'naya Tekhnika, No. 4, pp. 10–12, April, 1995.     

空压机轴承箱蜗壳温度探头油封改造

由于空压机进气侧轴承箱蜗壳温度探头密封效果不好,使空压机及其后续管道受到油污染。后将温度探头的O形圈密封改为骨架油封,杜绝了轴承箱漏油问题。文章简介空压机的结构和技术参数,详细介绍了骨架油封的制作和优点。     

Characteristics of mechanical properties of materials in studies of conditions of attainment of marginal states

It is shown that conditions of attainment of marginal states in the material of structural components are formulated on the basis of analysis of force and deformation criteria of formation and development of destruction. The parameters of these criteria are data on types of structural materials, standard and special characteristics of their mechanical properties, structural forms of considered elements of the equipment, and their operating stress loading. In this case, the construction of a system of state equations for describing interrelation of current damage, external actions, and responses to them is based on the concept of calculating variations in properties of materials at all stages of the design life cycle.     

Determination of parameters of microstructural inhomogeneity of deformation of metals by the method of modeling

The article suggests a method of evaluating the microstructural inhomogeneity of deformation of metals by modeling. The method includes the measurement of deformations of metal according to meshes of a dividing grid with small base and the calculation of the distribution parameters of microdeformations in model representation. It is shown that the modeling method makes it possible objectively to evaluate the microinhomogeneity of deformation of metals independently of the chosen mesh size of the dividing grid. New structural characteristics are introduced: the base and wave of variation expressing the degree of crumbling or amalgamation of metal grains by inhomogeneity of deformation.Translated from Problemy Prochnosti, No. 7, pp. 40–44, July, 1991.     

Analysis of the rate of propagation of the wave of change of boiling modes

An approximate analytical expression is derived for the velocity of the front of the wave of change of boiling modes on a rod and on a plate. The impact of the Thomson effect and of the heater orientation in the gravity field is included. Adequate agreement is demonstrated between the derived relations and experimental data.