Al、Ti含量对Inconel 718合金铸造组织和凝固行为的影响

采用差热分析(DSC)、光学显微镜、扫描电镜(SEM)、电子能谱(EDS)和X射线衍射分析(XRD)测试手段,结合JMatPro模拟计算分析研究了Al、Ti含量对Inconel 718铸锭组织和凝固行为的影响。结果表明,不同Al、Ti含量Inconel 718合金的铸态组织均呈典型树枝状结构,枝晶间析出相主要由(γ+Laves)共晶相和少量M(C,N)构成。随着Al/Ti原子比的升高,铸态组织中黑色枝晶间区域数量明显增加,Laves相形态由块状向共晶筛网状转变,同时Laves相周围析出的针状一次δ相和枝晶间γ″相数量减少;Inconel 718合金的凝固次序没有改变,合金的液相线由1363.5℃(合金Ⅰ)降低至1358.7℃(合金Ⅲ),而Laves相初熔温度和MC相固溶温度变化不大(不超过1.4℃);Nb,Mo,Ti元素在枝晶间的偏析程度随着Al/Ti原子比的升高而减轻。热力学计算结果显示,增加Al/Ti原子比可以提高γ′相数量,降低γ″相的数量。改型合金的硬度值随着Al/Ti原子比的提高而增加,当Al/Ti=4.32且(Al+Ti)=3.1at.%时,硬度值达到了345HV,比Inconel 718母合金硬度提高了23.7%。     

TiAl合金全片层组织的热稳定性研究

研究了Al含量、冷却速率和添加硼元素对TiAl合金全片层组织在1150℃的热稳定性的影响。研究表明:Al含量在46%～48%(原子分数,下同)范围的二元TiAl合金的Al含量越高,γ偏析程度越严重,铸造片层组织的热稳定性越差;Ti-48Al合金α单相区固溶处理后炉冷的粗片层组织的稳定性远远优于空冷的细片层组织,空冷细片层组织容易在晶界处发生不连续粗化转变,并且空冷片层晶粒内的魏氏片层(Lw)与基体的界面往往与晶界一同成为片层组织发生分解的起始部位;Ti-48Al合金中添加0.8%B因晶界TiB2相的存在能有效抑制细片层组织的晶界不连续粗化,但γ相从TiB2/基体界面和晶界重新形核生长可使片层组织转变为均匀的细晶近γ组织。     

定向凝固Ti-(43-48)Al-2Cr-2Nb合金的显微组织和性能

研究了Al含量对冷坩埚定向凝固Ti-(43-48)Al-2Cr-2Nb合金的显微组织和力学性能的影响。结果表明,Ti-(43-48)Al-2Cr-2Nb合金的定向凝固组织主要由α₂相和γ相组成,随着Al含量的提高α₂相逐渐减少而γ相含量提高,且其显微组织片层由以平行片层和45°片层为主的混合片层向垂直混合片层转变;Al含量(48%,原子分数)较高的Ti-(43-48)Al-2Cr-2Nb合金其片层取向与应力方向垂直,具有较高的抗压强度和较低的塑性;Al含量(45%,原子分数)适中的合金其片层取向与应力方向平行,具有较高的强度、室温延伸率和综合性能。     

Al含量对等值锌当量耐磨黄铜组织及性能的影响

为研究Al含量对耐磨黄铜组织、力学性能及摩擦磨损性能的影响,制备了三种不同Al含量(1.3％Al、2.4％Al、3.6％Al,均为质量分数)等值锌当量的耐磨黄铜合金;利用光学显微镜(OM)、扫描电子显微镜(SEM)、X射线衍射仪(XRD)、拉伸试验机及摩擦磨损试验机对三种耐磨黄铜的组织、力学性能和摩擦磨损性能进行了观察与研究.结果表明,合金的组织为α相、β相、共晶组织强化相及初生强化相,当锌当量不变时,随着Al含量增加,α相区、β相区面积基本相同,共晶组织强化相数量增加,初生强化相数量减少,导致强化相晶粒平均尺寸减小.随着Al含量的增加,合金的硬度、抗拉强度、屈服强度分别提高了31.6％、22.4％、67.3％,延伸率及磨损率分别下降了64.2％及40.8％.     

钽元素对Co-8.8Al-9.8W合金微观组织和力学性能的影响规律

为了研究合金化Ta(钽)元素对Co-8.8Al-9.8W高温合金微观组织和力学性能的影响,通过对Co-8.8Al-9.8W-xTa(x=0,1,2,4,6,原子分数,％,下同)合金微观组织和室温压缩性能的研究发现:铸态合金组织由γ基体相和衬度较亮的晶间相组成,枝晶间析出的白色衬度晶间相随着Ta含量的增加逐渐增多,并与γ基体相呈现出典型的共晶组织.经过1300℃/4 h的固溶处理和900℃/50 h的时效热处理,γ基体上析出均匀细小的γ'强化相,并且随Ta元素含量的增加,团簇状二次相(μ相、x相和β相)逐渐增多.Co-8.8Al-9.8W-xTa(x=0,1,2,4,6)合金在铸态和热处理状态下的显微硬度均随着Ta含量的增加而增加,其中,6Ta合金在铸态和热处理状态下均表现出最大的显微硬度,分别为567 HV和625 HV.室温压缩下,除1Ta合金外,其他合金的屈服强度σ0.2随着Ta元素含量的增加而逐渐增大,6Ta合金表现出1259 MPa的最大屈服强度;合金的极限抗压强度随着Ta元素含量的增加而先增大后减小,且在4Ta合金中表现出2522 MPa的最大抗压强度;所有合金中2Ta合金表现出22.95％的最大塑性变形能力.     

高Nb-TiAl合金的凝固组织与力学性能研究

研究了Al含量变化对高Nb-TiAl合金的凝固组织与力学性能的影响.结果表明:随着Al含量的增加,TiAl合金晶粒尺寸呈增加趋势;当Al含量为45.7%时,凝固过程中局部区域发生包晶转变,使晶粒尺寸显著增大;室温及700℃高温拉伸强度随着Al含量的增加而呈增加的趋势,但发生包晶转变致使室温及700℃高温拉伸强度下降约200MPa;Al含量对延伸率不敏感,持久性能随Al含量的增加呈增加趋势.为控制铸锭凝固后的组织与力学性能,尽量避开包晶转变区,合金中Al含量应低于45.7%.     

大尺寸(CrCoNi)94Al3Ti3中熵合金凝固行为

目的 制备大尺寸(CrCoNi)94Al3Ti3中熵合金(MEAs),并研究其凝固行为。方法 利用水冷铜坩埚悬浮熔炼技术制备大尺寸铸锭,通过金相(OM)、扫描电子显微镜(SEM)、能谱(EDS)等手段表征合金不同半径处的凝固组织和偏析行为,并采用Jmpro数值模拟软件预测合金可能存在的相,揭示大尺寸(CrCoNi)94Al3Ti3 MEA的凝固特点。结果 大尺寸(CrCoNi)94Al3Ti3 MEA的凝固组织为典型柱状树枝晶,随着冷却速率的变化,柱状晶形态和尺寸发生了明显变化。在凝固过程中,Ni、Al、Ti元素表现为枝晶间偏析,随着冷却速率的降低,偏析程度逐渐增大。(CrCoNi)94Al3Ti3基体为面心立方结构(FCC),在枝晶间(ID)存在少量块状的η相金属间化合物(Ni,Co)3(Al,Ti),同时在ID区域形成了大量不同纳米尺寸的L12相。结合相图可知,大尺寸(CrCoNi)94Al3Ti3 MEA的凝固路径为L→L+γ→L+γ+η→γ+η→γ+γ¢+η。结论 水冷铜坩埚悬浮熔炼技术制备的大尺寸(CrCoNi)94Al3Ti3 MEA无宏观偏析,该技术可以作为工程应用手段。     

脉冲电流参数对内燃机用Ti-44.5Al-3Nb-0.8Si合金凝固组织演变的影响北大核心CSCD

采用脉冲电流方法处理Ti-44.5Al-3Nb-0.8Si合金熔体的凝固过程,并测试不同脉冲电流条件下合金凝固组织性能,对组织结构的变化过程进行了深入分析。实验结果表明:当电流密度与频率都升高后,生成了互相垂直的枝晶结构,以及具有bcc晶体结构的β组织。随着电流密度增加,合金一次枝晶距离发生先降低后升高,最小值发生在电流密度为64 mA/mm^2时;当脉冲电流频率上升后,形成了距离更小的一次枝晶。脉冲电流下合金中形成了许多片层组织。当电流密度升高后,α2/γ相的片层间距发生了先降低后升高;提高脉冲电流频率会引起α2/γ组织的片层间距降低的现象,脉冲电流可以使TiAl合金形成更加细化的片层并提升均匀性。     

Mg-xLi-Al变形镁合金微观组织与拉伸性能

利用光学显微镜(OM)、扫描电子显微镜(SEM)、X射线衍射仪(XRD)分析了Li元素对MgxLi-3Al合金组织的影响,并用电子万能试验机测试合金的拉伸性能。结果表明,Li含量的变化可以明显改变合金的相组成。当m(Li)5.7%(质量分数)时合金由单一α-Mg相组成;Li含量在5.7%~10.3%(质量分数)之间时,合金为α-Mg+β-Li双相;m(Li)10.3%(质量分数)时合金为单一β-Li相。合金的塑性随Li含量的升高而增加,铸态LA113合金的延伸率高达37.36%,但挤压态下合金强度随Li含量升高而降低,挤压态LA53合金具有最佳抗拉强度,达到263.28MPa。当Li含量升高,合金中的第二相粒子会出现Al12Mg17转变为LiMgAl2。     

激光立体成形Rene88DT镍基高温合金沉积态组织研究

目的基于激光立体成形(Laser Solid Forming, LSF)过程中所存在的近快速凝固特性,以Rene88DT合金为研究对象,考察激光立体成形Rene88DT沉积态微观组织特征和相形成规律。方法通过LSF技术制备Rene88DT镍基高温合金单道沉积试样,采用光学显微镜(OM)和扫描电子显微镜(SEM)对组织进行观察,并用能谱仪(EDS)对试样中的析出相及微区成分进行分析。结果激光立体成形Rene88DT合金沉积态组织主要由沿趋于平行沉积方向生长的γ柱状晶组成,由于枝晶偏析的存在,以富Nb为主的块状MC碳化物以及板条状η(Ni_3Ti)相于枝晶间区域析出。随着沉积高度的增加,一次枝晶臂间距有所增大,二次枝晶臂逐渐发达,同时,γ'相体积分数和尺寸逐渐减小,沉积层的硬度相应降低。结论尽管激光立体成形熔池凝固已属于近快速凝固范围,熔池凝固过程中,溶质原子同样易于在晶界处形成偏聚,导致晶界弱化,在成形热应力作用下易形成沿晶裂纹。     

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.