热处理对Ag—Cu—Zn（-Sn）系925银合金力学性能和显微组织的影响

采用氩气保护水冷铜坩埚非自耗电极电弧熔炼制备了5种Ag-Cu-Zn（-Sn）系925银合金，并系统研究了热处理工艺对其力学性能和显微组织的影响。结果表明：含适量Zn、或Zn和Sn的925银合金，经700℃固溶0．5h后，硬度显著高于925Ag75Cu合金，且显微组织中出现大量退火孪晶；在200～250℃温度区间时效，硬度明显提高，且显微组织中出现浮凸状组织。     

时效对Cu-3.2Ni-0.75Si-0.30Zn合金组织和性能的影响

研究了时效温度和时效时间对Cu-3.2Ni-0.75Si-0.30Zn合金组织和性能的影响.结果表明,合金经900℃固溶,不同时间时效处理后,第二相呈弥散分布.合金经不同冷变形后时效,能获得较高的显微硬度与导电率,当时效温度达到500℃时,其显微硬度达到253.7Hv,导电率达到40%IACS.同时建立了该合金在500℃下,关于时效时间的一元导电率方程.时效前的预冷变形能够有力的促进合金在时效过程中第二相的析出,从而提高合金的显微硬度和导电率.     

固溶时效对热轧态QAl10.9-5-5合金组织及性能的影响

采用OM、XRD等分别研究了850~980℃固溶、350~650℃时效工艺对热轧态QAl10.9-5-5合金的显微组织及力学性能的影响。结果表明:随着固溶温度的升高,热轧态QAl10.9-5-5合金中未溶的α、κ相逐步固溶到高温组织中,并在室温组织中以β′相出现,当固溶温度升至925℃时,合金基本为单一均匀的β′相组织,此时硬度达到最大值;在随后的时效过程中,随着时效温度的升高,原子扩散速率加快,细小的κ相不断从β′相中析出,并产生明显的沉淀强化作用;当时效温度为450℃,保温2h时,合金硬度值可达326HB;继续升高时效温度,合金中开始出现大量的α相,从而导致其硬度随之下降。综合比较,热轧态QAl10.9-5-5合金的较佳热处理工艺为925℃×1h固溶、450℃×2h时效。     

快速凝固Mg-Zn-Y-Zr合金条带的组织和性能研究

采用普通凝固和快速凝固技术制备Mg-5Zn-1Y-0.6Zr合金,用XRD,SEM,显微硬度测量等分析方法研究其凝固组织和性能特征.结果表明,普通凝固合金由α-Mg固溶体和在晶界处呈不连续网状分布的三元相I-(Mg3Zn6Y)准晶相和W-(Mg3Zn3Y2)相组成.快速凝固合金晶粒细化并产生非晶相,晶间化合物全部转化为准晶I相.非晶相的出现及显微组织细化是造成快速凝固合金条带显微硬度提高的主要原因.快速凝固合金条带的显微硬度随冷速提高显著增大,最大值HV167.23是普通凝固合金的2.2倍.     

时效温度对含准晶相Mg93Zn6Y1合金的组织及性能影响

采用光学显微镜、扫描电子显微镜和X射线衍射及能谱分析,研究了铸态、固溶处理及在不同温度下时效处理的Mg93Zn6Y1合金的显微组织。发现铸态Mg93Zn6Y1合金显微组织主要由α-Mg和I相组成。经过固溶处理后,晶界处准晶相发生熔断,由铸态下的连续网状结构变为颗粒状。在不同的时效温度下,晶界处颗粒状准晶相长大且α-Mg晶内出现颗粒状准晶相。随着时效温度的升高,颗粒状准晶相发生长大,逐渐变为多边形状或鱼骨状。时效温度为300℃时,合金中准晶相大部分以颗粒状均匀分布在基体上。通过硬度及耐腐蚀性能测试,发现时效处理可大幅提高合金的硬度及耐腐蚀性能。其中,时效温度为300℃时效果最佳。     

Mg-Zn-xCu-Ce镁合金铸态组织与力学性能

利用光学显微镜(OM)、扫描电子显微镜(SEM)、X射线衍射(XRD)分析了Cu元素对Mg-Zn-xCu-Ce合金铸态组织的影响,并用显微硬度仪测试合金的显微硬度。结果表明:Cu含量的增加可以显著细化晶粒。当Zn,Cu质量比小于1时,合金枝晶间共晶组织由薄层状α-Mg+CuMgZn组成;当Zn,Cu质量比等于1时,合金中出现Mg2Cu相,同时共晶组织开始粗化;随着Cu含量的升高(Cu质量分数大于Zn),合金枝晶间共晶组织由α-Mg+CuMgZn+Mg2Cu组成,在形态上由薄层状转变为蜂窝状。合金的显微硬度随着Cu含量升高而增加。     

烧结温度对大电流电场烧结制备W-Mo-Cu合金的影响

利用大电流电场烧结工艺在875～1000℃的烧结温度下快速制备W-Mo-Cu合金,研究烧结温度对W-Mo-Cu合金微观组织、硬度及导电性的影响。基于合金烧结过程中的尺寸变化,通过拟合计算得到烧结特征指数,从而推断W-Mo-Cu合金烧结过程中的主要迁移机制。结果表明:烧结温度为875～975℃时,随着烧结温度升高,W-Mo-Cu合金中的孔隙减少,相对密度、显微硬度及电导率提高。当烧结温度为875～925℃时,W-Mo-Cu合金的致密化主要由塑性变形而非烧结引起。当烧结温度高于925℃时,W-Mo-Cu合金致密化过程中经历的主要迁移机制依次为塑性流动、体积扩散、晶界扩散和表面扩散。     

Nb含量对发动机用激光增材成形Inconel925镍基高温合金组织和硬度的影响

为拓展激光增材工艺(LAM)在Inconel925镍基高温合金加工与修复方面的应用,采用球磨合金化方法制备了Inconel925合金粉末,以LAM工艺加工不同Nb含量的Inconel925试样,分析了Nb含量对发动机用LAM成形Inconel925镍基高温合金组织和硬度的影响。研究结果表明:当Nb含量上升后,形成了更加明显的二次枝晶臂,随着Nb含量增大,开始形成清晰的二次枝晶臂;当Nb加入量提高后,沉积态试样中枝晶干γ相含有的Nb比例升高。经过固溶处理试样在显微组织方面存在显著差异性。当固溶温度上升后,在基体内溶入了更多的枝晶间Laves相,得到了更加均匀的组织。固溶态试样在显微硬度方面都表现为随Nb含量的升高而增大,在Nb含量11%时沉积态试样达到最高显微硬度。当固溶温度上升后,试样硬度降低趋势也变得更加平缓。     

ECAP对铜银合金组织和耐磨性能的影响

利用等径角挤压(ECAP)技术挤压铜银合金,对挤压后的铜银合金的组织和耐磨性能进行了研究.结果表明,ECAP实现了铜银合金晶粒的细化,由最初的5～6μm细化到2.5μm左右;并且硬度和耐磨性能都有提高,显微硬度提高70%,磨损失重降低19%左右.     

Y对Zn-25Al-5Mg-2.5Si合金铸态组织及力学性能的影响

以Zn-25Al-5Mg-2.5Si合金为基体材料,通过常规铸造方法制备了加入不同含量稀土Y的锌铝合金.采用扫描电镜、拉伸试验机、硬度计等分析研究了稀土Y对合金显微组织和力学性能的影响.实验结果表明,添加稀土Y后,在锌铝合金中,其与Al、Zn等元素形成硬度高、热硬性好的复杂成分化合物,分散于晶界和枝晶中,细化了组织,有效地阻碍了高温时基体的变形和晶界移动.随着Y含量的增加,在室温、100℃和180℃时合金的抗拉强度基本呈先升后降的趋势.当Y含量为0.4%(质量分数)时合金的综合性能最好,高温强度和硬度显著提高.180℃时合金的抗拉强度比不加Y时提高了26.4%,硬度提高了47.8%.     

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.     

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.