弥散相对3003铝合金再结晶晶粒尺寸的影响

针对3003铝合金冷轧板再结晶退火时出现的晶粒粗大问题,通过光学显微镜、扫描电镜(SEM)、能谱分析(EDS)、X射线衍射(XRD)、透射电镜(TEM)等方法,研究均匀化退火和中间退火过程中形成的弥散相的种类、尺寸和分布情况对3003铝合金再结晶晶粒尺寸的影响机理。结果表明:3003铝合金铸轧板的再结晶开始温度约为540℃;均匀化退火过程中形成的预析出的粗大弥散相对再结晶有促进作用,而细小弥散相对再结晶有抑制作用;中间退火过程中析出的弥散相对再结晶的抑制作用微弱;500℃中间退火200s后,板材基体内没有弥散相析出,此时再结晶优于弥散相析出率先发生;500℃中间退火2h后,板材基体内会析出大量细小的AlMnSi相;3003铝合金的最佳均匀化退火温度区间为560~580℃。     

铝镁异种金属复合挤压成形及界面微观组织

基于Deform 2D有限元模拟优化挤压工艺参数,在挤压速率2mm/s,挤压温度470℃下对铝镁双金属进行复合挤压实验,并采用扫描电镜(SEM)、显微硬度测试以及电子背散射衍射(EBSD)对复合挤压件界面结合层进行微观组织观察与分析。结果表明:在铝镁合金接触区反应生成了界面层,层内新的物相为靠近AZ31镁基体一侧的Al_(12)Mg_(17)以及靠近铝基体一侧的Al_3Mg_2。Al_3Mg_2相显微硬度值最高,平均值约为210HV,Al_(12)Mg_(17)相平均硬度约为170HV,因而界面区硬度高于两侧基体母材,形成典型的脆硬结合层,电子背散射衍射(EBSD)结果显示,Al_(12)Mg_(17)相的平均晶粒尺寸为30μm,Al_3Mg_2相的平均晶粒尺寸约为20μm,复合界面结合层区域晶粒取向各异,晶粒尺寸大小也不均匀,而复合外层纯铝基体取向区域均匀,新生成相在晶界上有部分再结晶发生。     

用强冷摩擦搅拌工艺制备超细晶紫铜板材

提出了一种制备整块、全板厚超细晶板材的强冷摩擦搅拌工艺，利用搅拌头与基材之间摩擦搅拌过程的剧烈塑性变形条件细化金属晶粒，通过搅拌位置的机械移动制备整块的超细晶板材．同时，采用强制冷却方式抑制动态回复和再结晶晶粒的长大，提高晶粒细化效果．建立了该工艺过程中应变速率、应变量及加热功率的数学模型，优化了紫铜板材细晶制备工艺参数，对所制得的细晶材料进行了硬度试验和显徽组织分析．结果表明，增强冷却能减小晶粒尺寸和提高细晶材料的硬度．制备出的超细晶紫铜板材布氏硬度可达HBS100，比退火紫铜的硬度约高一倍．     

Zr对Ti微合金化低碳钢形变奥氏体再结晶和析出相的影响

通过多道次模拟压缩实验，研究不同Zr和Ti含量的三种Ti微合金化低碳钢在950℃~1050℃形变奥氏体再结晶和析出相的变化和最佳变形温度。结果表明，Ti含量的提高和Zr的加入使Ti微合金钢形变奥氏体的再结晶和晶粒长大延迟。Zr的加入还能增加Ti微合金钢中析出相的数量、改善析出相尺寸分布的均匀性进而得到相对均匀的奥氏体组织。变形温度为1000℃时的Ti-Zr微合金钢奥氏体组织最细小均匀。     

变形温度对镁合金等通道转角挤压晶粒尺寸演变影响的有限元模拟

目的研究变形温度对AZ31B镁合金等通道转角挤压(ECAP)过程中晶粒尺寸演变的影响。方法建立AZ31B镁合金动态再结晶和晶粒长大数学模型,采用Fortran语言编写晶粒演变子程序,并通过商用有限元软件MARC的二次开发接口,建立耦合微观组织演变的AZ31B镁合金等通道转角挤压有限元模型,研究变形温度对等通道转角挤压过程应变场、再结晶百分数和晶粒尺寸的影响规律,并与实验结果进行比较。结果随变形温度从200℃增至400℃,原子热激活效应增强,再结晶百分数从75.37%增加至99%,平均晶粒尺寸从6.67μm增加至25.7μm,且晶粒尺寸分布均匀性增大,但是200℃变形的ECAP试样出现开裂。结论在250~300℃温度区间内进行ECAP变形,有助于获得细小均匀的微观组织,同时避免出现变形开裂。     

Mn-Cr齿轮钢动态再结晶行为及组织演变

采用Gleeble 1500热模拟试验机研究了一Mn-Cr齿轮钢在变形速率为0.1～1 s-1、变形温度为900～1150℃、原始奥氏体晶粒尺寸为70～150 μm条件下的动态再结晶行为及再结晶奥氏体晶粒尺寸的变化规律.实验结果表明,Mn-Cr齿轮钢在温度较高,应变速率较低及原始奥氏体晶粒较细的情况下变形时,表现出典型的动态再结晶行为.再结晶发生的条件为Zener-Hollomon参数小于某一临界值(Zc).再结晶晶粒按晶界突出机制形核.通过回归分析,确定该齿轮钢的再结晶激活能为378.6 kJ/mol,应力指数为5.8.Z参数控制形变储存能,因而唯一地决定动态再结晶晶粒尺寸Ds,二者符合关系式Ds=1.3×105Z-0.25.     

镍基合金完全再结晶后的晶粒长大行为研究

目的 研究镍基合金完全再结晶后的晶粒长大行为.方法 首先通过两道次热压缩实验获得镍合金完全再结晶组织,然后对完全再结晶的组织进行退火热处理使晶粒长大.采用电子背散射衍射实验研究发生长大的晶粒组织形貌与尺寸变化规律.结果 完全再结晶后的退火工艺参数对平均晶粒尺寸有显著影响.完全再结晶后的晶粒能够在较高的退火温度和较长的退火时间下快速长大.基于实验结果,建立了能够准确描述镍基合金完全再结晶后晶粒长大行为的动力学模型.结论 为了有效抑制完全再结晶后的晶粒长大行为,退火温度不宜升高,退火时间不宜过长.晶粒尺寸的调控工艺参数可以参考所建立的晶粒长大模型来选择.     

C194合金连续挤压全过程的组织与性能演变

采用光学显微镜、透射电子显微镜(TEM)、维氏硬度仪和万能材料试验机等手段对C194合金连续挤压全过程的组织演变与性能特征进行研究。结果表明,C194合金连续挤压过程没有出现明显的动态再结晶组织,仅在直角弯曲后变形区观察到少量沿晶界择优析出的不完全动态再结晶细小晶粒;各变形区硬度随变形量的增加由88.7HV提升至136.1HV,并在直角弯曲后变形区增长减缓;挤压前后材料抗拉强度由263 MPa提高到476 MPa,延展性则由26.5%降至18.7%;挤压过程中发生第二相析出,析出物呈现尺寸为60~80nm的椭球形和尺寸为10~20nm且弥散分布的微小颗粒两种形貌。     

挤压Zn-Cu-Ti合金的组织及其力学性能

采用Zn-Ti中间合金等制备了不同铜含量的锌合金,370℃/4h均匀化后在300℃对合金进行了热挤压加工。通过X射线衍射分析、扫描电镜分析和能谱分析以及力学性能测试,研究了合金的微观组织和力学性能之间的关系。结果表明,Zn-Cu-Ti合金主要由锌的固溶体η相,TiZn15相和CuZn4相组成,Ti元素的加入细化了合金的显微组织,提高了合金的力学性能;热挤压过程中,合金发生动态再结晶和局部再结晶晶粒长大现象,TiZn15相和CuZn4相被破碎后沿挤压方向分布于晶界处,有助于阻碍再结晶晶粒的长大;Cu含量在0.5%~3.0%范围内,随着含铜量的增加,Zn-Cu-Ti合金的强度和硬度增大,当Cu含量超过2.0%时伸长率有下降趋势;由于挤压过程中发生了动态再结晶在一定程度上抵消了加工引起的硬化,合金挤压态硬度较铸态硬度提高不大。     

初始宽度对AZ31轧制板材组织与性能的影响

在相同条件下轧制了不同初始宽度的AZ31板坯,通过对轧后板材的组织观察、硬度测试、XRD和SEM实验,研究了初始宽度对AZ31板材轧制组织和性能的影响.结果表明:初始宽度对AZ31镁合金轧制板材有一定影响;随着板坯宽度增加,轧后板材边部的硬度有所增加,再结晶晶粒比例增大,(0002)基面取向有所增加;板材中间部分的动态再结晶进行得更加完全,硬度比边部低,(0002)基面取向显著增加.     

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.     

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。     

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.     

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.     

Analysis of anisotropy of properties on the basis of studies of texture of coarse-grained ingots of thermoelectric materials

An analysis of anisotropy of the properties of a Bi₂Se_0.3Te_2.7 solid solution was carried out using construction of demonstrative surfaces for thermoelectric effectiveness and thermal expansion coefficients. It is shown that the texture is an important factor forming anisotropy of properties and technological fitness of ingots for manufacturing modules. Anisotropy of properties based on the studies of the ingot textures obtained using the float-zone method and Bridgman method (growing thermoelectric plates in a flat cavity) was studied.