Cu-Al2O3纳米弥散强化铜合金的短流程制备工艺及性能

研究了一种简化的短流程工艺,成功地制备出几种不同成分的Cu-Al2O3弥散强化铜合金.对Cu-0.3wt%Al合金粉末内氧化的研究表明,在700℃～900℃内氧化时,早期进行得非常迅速,硬度的提高主要发生在1 h以内;不同温度下内氧化达到硬度峰值的时间也各不相同,且900℃内氧化时硬度的峰值为最高(HV=141).随Al2O3体积分数的增加,挤压态合金σb和σ02均逐渐升高,但其增速随Al2O3的增加有逐渐减缓之势.经不同变形量的冷拉拔后,σb和σ0.2基本呈相对均匀的速度增加,且随Al2O3含量的增加,加工硬化的速率逐渐变慢,延伸率则相应降低,电导率的下降幅度不大.所有Cu-Al2O3合金在退火后均能保持其大部分强度(≥72%).     

时效工艺对Cu-Te-Cr合金性能的影响

研究了在不同时效温度下,时效时间对Cu-Te-Cr合金力学性能和电学性能的影响.利用扫描电镜和能谱仪分析了析出相的形貌、组成及其分布.研究表明,随着时效时间的延长,合金硬度和导电率都先快速上升,然后缓慢下降,出现一个类似峰值点.且温度越高,达到峰值所需的时间越短;随着Te含量的增加,合金硬度减小,而导电率则相对提高.这是由于随时效时间的延长和时效温度的提高,合金发生晶粒长大和第二相析出、从而提高合金硬度和导电率;随时效的进一步进行,部分第二相发生重溶,晶粒进一步长大,合金硬度和导电率缓慢下降.     

Cu-3.0Ni-0.75Si合金时效析出动力学分析

为研究Cu-3.0Ni-0.75Si合金时效过程中沉淀相的析出与长大规律,及其对合金硬度的影响,采用涡流电导仪和布氏硬度计分别测量合金的电导率和硬度,根据导电率与新相析出量之间的关系分析合金的时效析出动力学过程.结果表明,在350℃下时效,合金硬度随时效时间的延长,先升高后趋于平缓;在450℃、550℃下时效,合金硬度随时效时间的增加快速上升,到达峰值后缓慢下降;时效温度越高,合金硬度峰值越低,但硬度达到峰值所需的时间越短.温度一定,随时效时间的增加,合金电导率在时效初期快速升高,至峰值后趋于平缓.根据Cu-3.0Ni-0.75Si合金在450℃时效过程中电导率的变化,通过Avrami方程推导出相应的相变动力学方程及电导率方程分别为f=1-exp(-0.052 2t0.717 61)和σ=15.2+16.3[1-exp(-0.052 2t0.717 61)],采用相关系数检验法及F检验法对电导率方程的可信性进行检验,结果说明时效析出动力学方程和电导率方程具有一定的可靠性.对比由电导率经验方程得出的电导率理论值与测量得出的实验值,该理论值与实验值有良好的吻合度.     

内氧化-高速压制法制备Al_2O_3弥散强化铜合金的性能研究

以Cu-0.18%(质量分数)Al合金粉末为原料、Cu2O为氧化剂,采用内氧化法制备Al2O3弥散铜合金粉末,采用高速压制(HVC)对粉末进行成形,经氢气中960~1 080℃烧结制备弥散强化铜合金,研究合金粉末的HVC成形效果和烧结温度对合金致密度、硬度、导电率和压缩强度等性能的影响。结果表明,HVC成形Al2O3弥散铜合金粉能获得良好的成形效果,压坯密度达到8.71 g/cm3(98.4%致密度)。与压坯相比,烧结后合金的致密度并无明显变化,但其导电率显著提升,硬度有所降低,压缩强度升高。随烧结温度的升高,合金的导电率有所升高,硬度略有降低,压缩强度基本保持恒定。经1 040~1 080℃烧结制备合金的导电率、硬度分别达到80%IACS和77 HRB以上,压缩强度达到450 MPa,能基本满足点焊电极的实际应用需求。     

FeCrAl-ODS合金的高温水蒸气氧化行为

目前有关FeCrAl-ODS钢在高温水蒸汽下的氧化过程中氧化膜结构的演变少有分析研究.以FeCrAl-ODS合金为研究对象,采用XRD、SEM、EPMA、EDS等分析手段,在700～1100℃条件下开展了高温水蒸气氧化试验,从氧化动力学和氧化层结构形貌、物相、成分等方面研究了其高温水蒸气氧化行为.研究结果表明:在700～1100℃,FeCrAl-ODS合金高温水蒸气氧化动力学满足抛物线增重规律,抛物线速率常数Kp随温度增加而增大.高温水蒸气氧化96 h后,700℃时FeCrAl-ODS合金表面氧化层以Fe2O3为主;900℃时FeCrAl-ODS合金表面氧化层的外层以Fe2O3为主,内层以A12O3为主,氧化层比较疏松,不能很好地对基体起到保护作用;1100℃氧化过程中,在不同氧化时间段氧化层均为单层致密的Al2O3氧化层结构.     

内氧化制备Cu-5％Al2O3复合粉末的研究

采用内氧化法制备Cu-5％Al2O3(质量分数)复合粉末,通过XRD、SEM-EDX、TEM等检测手段对粉末结构性能进行分析.结果表明,通过合理控制气氛和内氧化参数,Cu-Al中Al能够脱溶并被氧化.在内氧化温度为900℃条件下,0.5h时内氧化程度不理想;延长到1h时,内氧化能够基本完成.能谱分析表明,Al元素分布出现局部偏聚,主要是由内氧化过程中Al反向扩散引起的.电子衍射花样标定表明,晶内生成了近球形的γ-Al2O3,尺寸为10～40 nm;晶界形成粗大的α-Al2O3,形貌呈近球形(约200 nm)和条枝状,条状粒子长约200 nm,宽约100 nm.粉末的显微硬度最高达到105.05HV.     

固溶+时效处理对粉末冶金Ti-22Al-25Nb合金显微硬度的影响

采用放电等离子烧结技术(SPS)在950℃/80 MPa/10 min条件下制备粉末冶金Ti-22Al-25Nb(原子分数,%)合金作为初始材料,将其分别在940~1100℃、10~120 min和800℃/8 h条件下进行固溶处理和时效处理,研究了固溶+时效处理对粉末冶金Ti-22Al-25Nb (原子分数,%) 合金的微观组织和显微硬度的影响,并建立了显微硬度的演变模型。结果表明,随着固溶温度的提高和保温时间的延长B2相的晶粒尺寸增大、均匀度提高,在940~1010℃晶粒长大的速率最低,在1100℃晶粒尺寸的均匀度达到最大值0.84。板条O相的尺寸和数量对合金的性能有显著影响。在(B2+O)两相区时效后,其尺寸和数量显著影响合金性能的次生板条O相的体积分数提高、尺寸减小,尤其是相互交叉、缠结的O/O相数量的增多,使合金的显微硬度提高;在1060℃/60 min/Water cooling(WC)+ 800℃/8 h/Furnace cooling(FC)条件下处理的合金,其显微硬度达到最大值434.92 HV。     

热处理对Ni-P-A12O3化学复合镀层摩擦磨损性能的影响

热处理可显著提高镀层的硬度和耐磨性能。采用化学镀的方法在45钢表面制备了Ni-P-纳米A12O3复合镀层,并以不同温度对其热处理,研究了镀层热处理前后的物相、硬度和耐磨性能。结果表明：400℃热处理后,Ni-P-A12O3复合镀层达到稳态,稳定相是Ni＋Ni3P＋NiO＋A12O3;镀层的显微硬度随热处理温度的升高而先...     

Ni-α-Al2O3纳米复合电镀工艺的优选及镀层的硬度和耐蚀性

为了提高Ni-Al2O3纳米复合电镀层的硬度和耐蚀性,以正交试验对镀液温度、电流密度、α-Al2O3纳米粒子质量浓度等因素进行了优选,采用扫描电镜、能谱仪、硬度仪及电化学工作站分别研究了镀层的微观形貌、能谱、硬度和耐蚀性。获得了最优工艺条件:镀液温度65℃,阴极电流密度2 A/dm2,Al2O3加入量为10g/L;在此工艺条件下所得Ni-α-Al2O3纳米复合镀层晶粒细小、表面平整、光滑,显微组织致密、均匀,镀层的硬度及耐蚀性比纯镍镀层均有显著提高。     

Ni—a-Al2O3纳米复合电镀工艺的优选及镀层的硬度和耐蚀性

为了提高Ni-Al2O3纳米复合电镀层的硬度和耐蚀性,以正交试验对镀液温度、电流密度、a-Al2O3纳米粒子质量浓度等因素进行了优选,采用扫描电镜、能谱仪、硬度仪及电化学工作站分别研究了镀层的微观形貌、能谱、硬度和耐蚀性。获得了最优工艺条件：镀液温度65℃,阴极电流密度2A／dm2,Al2O3加入量为10g／L;在此工艺条件下所得Ni-a-Al2O3纳米复合镀层晶粒细小、表面平整、光滑,显微组织致密、均匀,镀层的硬度及耐蚀性比纯镍镀层均有显著提高。     

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.     

Assessment of intakes of mixtures of radionuclides

Australia has several uranium mines and a large number of mineral sand mines, with associated processing facilities. Exposures resulting from these mining and processing operations usually involve intakes of mixtures of radionuclides. This work describes the development of a suite of first order, linear compartment models, based on the ICRP Publication 66 respiratory tract model, and an analytical solution to the decay equations, for assessing the consequences of such intakes. The computer programs based on these models directly compute excretion, organ retention and organ and whole-body doses for intakes of either single radionuclides or any mixture of radionuclides belonging to the same radioactive decay chain. The intake can be via inhalation, ingestion or injection, and can be acute, chronic or of limited duration. The starting concentration and degree of secular (dis)equilibrium can be specified for each radionuclide. No assumptions need to be made about the relative magnitudes of the radioactive half-lives of the different nuclides.     

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.     

卧式金属罐容量的测量结果不确定度

本文根据多年的实践检定经验 ,参照JJF1 0 59- 1 999《测量不确定度评定与表示》以及《测量不确定度表达 1 0讲》 ,对卧式金属罐容量的测量结果不确定度进行了评定。     

盐酸浓度不确定度的评估

通过对盐酸浓度标定的过程分析，找出影响结果的各个分量，进行不确定度的评定，按照计量技术规范给出标准的表示法。     

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.