TC6钛合金的超塑变形机制研究

提出了一种全新的超塑性研究方法：基于m值的高效超塑变形机制。采用该方法对TC6钛合金进行高温拉伸实验,研究其超塑性能,并与最大m值法超塑性进行比较分析。实验结果表明,细晶组织的该合金具有优良的超塑性,最佳变形温度在900℃,最大m值超塑变形可以获得20倍的最大延伸率;基于m值的高效超塑变形可以显著提高超塑成形效率,在获...     

Al-6Mg-0.2Sc铝合金高温力学行为研究

研究了Al-Mg-Sc超塑合金在200～500℃的高温力学性能,并对实验残样进行了微观组织分析.结果表明,Al-Mg-Sc合金在250～500℃区间内均具有一定的超塑性;在300～400℃超塑成形时强度较低,成形后制件使用性能较好,工程化条件下可选择使用;合金高温断裂机制由穿晶断裂向沿晶断裂转变的温度点在300℃附近,在此温度以下晶粒强度低于晶界强度,在此温度以上晶粒强度高于晶界强度.     

钛合金的氢处理技术及其对超塑性的影响

氢处理技术是通过氢的可逆合金化作用,对钛合金的微观组织、力学性能和加工性能进行调整的一种新兴热加工技术.钛合金中氢的加入可以增加钛合金中塑性相的体积分数,降低流动应力,提高超塑性性能,从而降低钛合金的超塑性变形对变形速率和变形温度的苛刻要求.利用氢处理与塑性变形相配合制备晶粒尺寸小于1μm的超细晶,使钛合金在更低的变形温度和更高变形速率下呈现出超塑性,是攻克钛合金扩大应用瓶颈的一条新途径.     

高强度超细晶金属材料塑性行为及增塑研究进展

强度和塑性是金属结构材料最重要的力学性能指标,金属高性能化的关键是在高强度水平下保证良好的塑性,然而两者往往不能兼顾。在众多强化方法中,晶粒细化长期以来被认为是强化金属最理想的手段,在传统晶粒尺寸范围,细化晶粒既可以显著提高材料的强度,又能改善材料的塑韧性。因此,近几十年来超细晶/纳米晶金属得到了广泛研究和发展,出现了以大塑性变形(SPD)、先进形变热处理(ATMP)技术为代表的超细晶制备方法,所得晶粒可以细化到亚微米或纳米尺度,金属性能大大提高。然而,大量研究证实当晶粒细化到亚微米或纳米尺度时金属强度提高但塑性显著下降,与传统的细晶强化规律不符。对此,国内外学者进行了很多研究,试图阐明其机理、揭示晶粒超细化导致塑性降低的物理本质。此外,由于细化晶粒方法受到塑性的限制,新的高强度水平下增强塑性的方法成为钢铁材料高性能化的研究热点。针对塑性下降的事实,为了进一步提高超细晶金属材料性能,研究者开展了许多增强塑性的工作,获得了较好的效果,但仍存在一些不足。关于金属晶粒超细化导致塑性降低的普遍共性现象,目前广泛认可的理论主要有晶界捕获(吸收)位错的动态回复理论、位错运动湮灭理论、高初始位错密度以及位错源缺失机制等。前三者都主要关注超细晶金属材料低(无)加工硬化能力,并将其归结为延伸率降低所致。主要是因为低(无)加工硬化使材料在变形早期发生塑性失稳或局部变形从而表现出低塑性。超细晶金属增塑研究主要体现在增塑方法和机理方面,目前,增塑方法主要有(1)形成纳米孪晶;(2)获得粗晶-细晶双峰组织;(3)利用相变诱发塑性/孪生诱发塑性(TRIP/TWIP)效应;(4)引入铁素体软相;(5)利用纳米第二相粒子等。这些增塑方法的主要机理是利用组织结构的改变提高超细晶金属的加工硬化能力以维持良好的均匀塑性变形以及利用组织相变提高塑性。本文归纳了常用的超细晶金属制备方法,综述了超细晶金属材料塑性降低的研究进展,总结了超细晶金属增塑的研究结果,分析了目前研究中存在的不足,探讨了超细晶金属增强增塑的发展趋势,以期为超细晶金属塑性降低理论及增强增塑研究提供参考。     

GH4169集合器超塑成形有限元分析及预成形研究

为了成功超塑成形GH4169高温合金集合器并降低研制成本,采用有限元分析对GH4169合金集合器超塑成形过程进行了数值模拟,并采用拉深成形工艺对集合器超塑成形所需的预成形进行了研究.结果表明:超塑成形需筒形预成形件,且聚料工步是超塑成形出满足设计要求的零件所必需的一道工序;成功地拉深出集合器超塑成形预成形件;合金经预拉深成形后,在超塑成形温度(950℃)下保温30 min后仍是ASTM 10级以上的细晶组织,能够满足超塑成形所需的细晶组织的要求.     

钛合金的应用现状及加工技术发展概况

钛合金具有密度小、强度高、耐高温和抗腐蚀性好等优点,在航空航天、船舶、汽车、医疗、化工和能源等领域获得了广泛的应用.首先从航空航天和非航空航天领域综述了钛合金的应用现状;然后从热处理、焊接性能和表面处理技术三个方面综述了钛合金加工工艺及性能;最后叙述了钛合金的最新成形技术,即超塑性成形技术、近净成形技术、激光成形制造技术及计算机模拟技术,并展望了钛合金的应用前景及发展方向.     

钛合金室温超塑探索研究

对钛合金室温超塑性行为进行了一些探索研究,其中包括在室温条件下在0.5～1s内进行快速压缩超塑试验,并且要求达到80%左右的大变形量,以及开展相关性能、组织等方面的研究,为今后钛合金室温超塑方面的进一步研究提供一些参考.     

大塑性变形制备细晶材料的研究、开发与展望

系统介绍了大塑性变形(SPD)细化晶粒的条件和目的,综述了4种主要的大塑性变形工艺的基本原理、特点和应用,剖析了细晶材料的强度和超塑性特征,展示了大塑性变形制备细晶材料的诱人前景和发展方向.     

超塑处理对喷射成形GCr15钢超塑性的影响

研究了超塑处理对喷射成形GCr15钢超塑性的影响，超塑性拉实验结果表明，未经超塑处理的铸态试样，延伸率为119％，经过二次油淬和二次油淬＋高温回火超塑处理的两种试样，延伸率分别为328％和671％，变形温度和应变速率对GCr15钢的超塑性有一定的影响，但材料的微观组织对其超塑性具有决定性作用，超塑处理改变了材料试样的微观组织，导致其超塑性发生变化，经过二次油淬＋高温回火超塑处理后试样具有球化组织，其超塑性最好，未经超塑处理的铸态试样具有珠光体组织，超塑性最差，经过二次油淬超塑处理后试样的组织是马氏体和少量碳体物的混合，其超塑性介于上述两种试样之间，喷射成形工艺使GCr15钢获得均匀细化的稳定组织，这对于细晶超塑性是必要的，超塑处理材料的超塑性得到更大的提高。     

应用等通道转角挤压(ECAP)技术制备超细晶钛合金

等通道转角挤压(equal channel angular pressing,ECAP)是一种强塑性变形技术,能有效细化材料的微观组织,提高材料性能,改善难变形材料的成形性.简述了ECAP技术制备超细晶钛合金的原理和技术现状,分析了不同工艺参数对钛合金ECAP变形过程和材料性能的影响以及晶粒细化的微观机制.     

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.     

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 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.     

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.