5A90铝锂合金超塑性变形机理的定量研究

通过聚焦离子束在5A90铝锂合金试样表面蚀刻微米尺寸高分辨网格,在温度480℃、初始变形速率1×10~(-3)s~(-1)的变形条件下,定量研究其超塑性变形过程中晶界滑移和晶内位错滑移对总变形的贡献量,并采用扫描电镜、电子背散射衍射观察合金超塑性变形的组织演变作为佐证。结果表明:位错运动在超塑性变形初期(ε0.65)的贡献量约为60%～80%,为主要变形机制,在该阶段条带状晶粒逐渐细化和等轴化,平均晶粒尺寸减小约40%,晶粒转动作为协调机制;随着应变量的增大,发生明显的动态再结晶,晶粒尺寸开始增大,晶内位错滑移的作用逐渐减小,晶界滑移成为变形的主要机制。     

搅拌铸造SiCp/2024复合材料热挤压-轧制变形组织及性能

利用搅拌铸造-热挤压-轧制工艺制备SiCp/2024复合材料薄板。通过金相观察(OM)、扫描电镜(SEM)及力学测试等手段研究了该复合材料在铸态、热挤压态及轧制态下的显微组织及力学性能,分析了材料在塑性变形过程中显微组织及力学性能的演变。结果表明,该复合材料铸坯主要由80～100μm的等轴晶组成,粗大的晶界第二相呈非连续状分布,SiC颗粒较均匀地分布于合金基体中;热挤压变形后,晶粒沿挤压方向被拉长,SiC颗粒及破碎的第二相呈流线分布特征;轧制变形后,基体合金组织进一步细化,晶粒尺寸为30～40μm,SiC颗粒破碎明显,颗粒分布趋于均匀,轧制变形对挤压过程中形成的SiC颗粒层带状不均匀组织有显著的改善作用。数学概率统计指出,塑性变形有利于提高颗粒分布的均匀性。力学测试表明,塑性变形后,复合材料的抗拉强度、屈服强度和延伸率显著提高。SiCp/2024铝基复合材料主要的断裂方式为:合金基体的延性断裂、SiC颗粒断裂及SiC/Al界面脱粘。     

CeO2掺杂对AlCoCrCuFe高熵合金的组织结构与摩擦磨损性能的影响

采用熔铸法制备等摩尔比的AlCoCrCuFe高熵合金。利用X射线衍射仪、扫描电镜、能谱分析仪、显微硬度计和摩擦磨损试验机分别测试CeO2掺杂前后对其物相结构、显微组织和摩擦磨损性能的影响。结果表明:AlCoCrCuFe由BCC和FCC双相组成,合金中掺杂1%(质量分数)CeO2后引起衍射峰强度的显著提高。两种合金显微组织均为典型树枝晶,Cu与Ce元素在晶间富集,枝晶内为调幅分解组织。CeO2的加入使合金显微硬度从441.5HV增加到475.3HV,摩擦因数与质量损失率分别从0.55,1.44%降低到0.4,1.28%。     

行星轧制变形程度对TP2铜管材组织及性能的影响

目的研究行星轧制变形程度对TP2铜管材在轧制和联拉时的组织和性能的影响。方法采用金相显微分析和拉伸实验,研究行星轧制变形程度对TP2铜管铸坯轧拉态以及拉拔态组织及性能的影响规律。结果经连续铸造的TP2铸坯为柱状晶,且由外向内成长。经行星轧制、联拉后的管材晶粒纤维流线,其晶粒显著拉长,随着轧制变形程度的增加,流线减弱,晶粒更加细化。轧制变形程度为93%与90%的轧管屈服强度、抗拉强度分别降低了22.83%和7.59%,伸长率提升了4.44%,塑性变形能力增加。结论随着轧制变形程度的增加,联拉管抗拉强度略有提高,而伸长率得到了保持。     

拉拔和轧制变形铝导线的结构演化及力学与导电性能

对工业用A4纯铝进行拉拔和轧制两种塑性变形,研究了纯铝导线材料的微观结构演化、强度和导电率。结果表明:在变形量较小时拉拔变形和轧制变形后纯铝铝导线主要由拉长晶粒组成,这些拉长晶粒由位错亚结构组成的小角晶界组成;在相近的等效应变变形情况下,轧制样品中高角晶界的比例更高。拉拔变形后样品的强度和塑性均优于轧制变形后的样品。拉拔变形使材料具有更高强度和导电率。探讨了材料的导电性与形变强化间的关系。     

热轧变形对5052铝合金组织与力学性能的影响

通过光学显微镜、扫描电镜、能谱和X射线衍射分析和拉伸实验等试验分析方法,研究不同热轧变形量(54％、75％)对5052铝合金微观组织和力学性能的影响.结果显示,变形量可显著影响5052铝合金的热变形组织及其力学性能.随着轧制变形量的增加,晶粒被显著拉长,晶界处粗大第二相沿晶界被拉长,甚至被破碎.但是其第二相的组成并没有随着轧制变形量的增加而变化,铸态和轧制态的5052铝合金均由α-Al、Al82Fe18和Mg2Si三相组成.同时随着轧制变形量的增加,其综合力学性能提高,即沿轧制方向且轧制量为75％时的5052铝合金呈现出最优的综合力学性能.     

合金成分对镍基合金激光熔覆涂层组织与性能的影响

为了研究激光熔覆镍基合金涂层显微组织与性能之间的关系,本文选用Ni25、Ni45、Ni60镍基自熔性合金粉末作为熔覆材料,在同一工艺参数下在45#钢基体上制得Ni25、Ni45、Ni60合金激光熔覆涂层。利用扫描电子显微镜(SEM)、能谱仪(EDS)、X射线衍射仪(XRD)、显微硬度计等方法对涂层的显微组织、物相组成、显微硬度等进行了研究。结果表明从Ni25到Ni60合金涂层,随着合金元素含量的提高,涂层微观组织逐渐由亚共晶转变为过共晶,γ-Ni奥氏体枝晶所占体积分数减少,尺寸细化,枝晶间的共晶组织和硬质相所占的体积分数增大,涂层和基体之间结合带的宽度越来越窄,熔覆层的显微硬度越来越高。Ni25、Ni45合金涂层的平均显微硬度分别为250HV和550HV左右,而Ni60合金涂层的平均硬度却高达750HV左右,为Ni25合金涂层的3倍。     

TiCu_(0.5)Al_(0.5)Cr_(0.2)Ni_(0.1)高熵合金微观组织及性能研究

采用X射线衍射仪、光学显微镜、扫描电镜和透射电镜对TiCu_(0.5)Al_(0.5)Cr_(0.2)Ni_(0.1)高熵合金的相组成、相形貌、元素分布进行了系统研究,利用显微维氏硬度计测量了合金在室温下的硬度,通过电子万能试验机对合金进行了室温压缩试验,并在实验室模拟环境下进行合金防腐防污性能研究。结果表明:TiCu_(0.5)Al_(0.5)Cr_(0.2)Ni_(0.1)高熵合金主要由六方晶系Ti(CuAl)_2组成,大块状Ti(CuAl)_2相间存在条状组织,条状为AlCu_2Ti相,条间为CuTi_2相。树枝晶(DR)内Al元素和Cr元素含量较高,枝晶间(ID)Ti元素含量高于枝晶区域,而Ni元素和Cu元素整体分布较均匀。枝晶间(ID)显微硬度平均值为772HV,树枝晶DR显微硬度为690HV,枝晶间(ID)显微硬度高于树枝晶(DR)的;室温压缩强度为1 091 MPa。合金耐腐蚀性能良好,60℃人造海水中合金腐蚀失重量仅为-0.000 05 g,并具备一定的防污功能。     

AZ31镁合金轧制工艺的研究

对AZ31镁合金在400℃条件下的轧制工艺进行了研究,在不同压下量、不同道次条件下分别进行了轧制实验,并对轧制后AZ31板材的组织和力学性能进行了研究。实验结果表明:在400℃条件下,以小变形量轧制,每道次压下量为1mm时,较好的加工工艺条件为轧制到第8道次,累积变形量50%;每道次轧制压下量为2mm时,较好的加工工艺条件为轧制到第2道次,累积变形量为25%;AZ31镁合金在大变形量下轧制易产生裂纹,裂纹的产生可能是由于随着累积变形量增加,内应力激增,在难变形的硬取向晶粒区或第二相处产生应力集中,萌生裂纹。裂纹尖端扩展经过的区域变形量较大,因而裂纹两侧存在再结晶细晶区域。     

冷轧对Al_(10)Cu_(25)Co_(20)Fe_(20)Ni_(25)高熵合金组织结构及力学性能的影响

对铸态Al10Cu25Co20Fe20Ni25高熵合金进行冷轧处理后进行室温拉伸测试,并利用X射线衍射仪(XRD)和扫描电镜(SEM)分别对其相结构、微观组织形貌及拉伸断口进行分析。结果表明:经冷轧工艺处理后,Al10Cu25Co20Fe20Ni25高熵合金硬度最大为285HV,较轧制前提高了51.6%;在变形量为40%时,抗拉强度达到最大值,为638MPa,是铸态合金的2.7倍。拉伸断口分析表明,铸态合金的断裂模式为树枝晶沿晶断裂和韧窝型延性断裂,而冷轧态合金主要为韧窝型延性断裂模式。     

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.     

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.     

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.     

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.     

Numerical study of methods of linearization of the output characteristics of radio-frequency sensors of the level of dielectric media

Different constructions of the sensing elements of radio-frequency level sensors based on sections of long lines are numerically investigated by means of the Matlab program for the purpose of minimizing the measurement error caused by the nonlinearity of the output characteristic. It is shown that the nonlinearity is lowest for U-shaped designs. The nonlinearity factor KN may be regulated by varying the capacitance of a correcting capacitor connected to the input of the sensing element and (or) the length of one of the sections of the long line. In selecting an optimal capacitance of the correcting capacitor KN ≤ 0.15% for control media with dielectric permittivity in the range 2.2–30.     

Possibilities of Decreasing the Errors of Determination of the Height of the Pole of a Sessile Drop of Melt

We analyze the possibilities of decreasing the errors of measuring the height of the pole of a sessile drop of melt above its equator by determining the position of the equator according to the midpoints of vertical chords of the image of the drop. The optimal distance between these chords and the edge of the image of the drop is chosen within 10–20% of the radius of the equator. The proposed method guarantees the same level of errors of evaluation of the height of the pole and the radius of the equator, which enables one to substantially increase the accuracy of evaluation of the capillary constant and the surface energy of the melt according to the geometric parameters of the sessile drop.     

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.     

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.