镍基单晶高温合金固溶处理制度的研究进展

单晶涡轮叶片是航空发动机的关键热端部件,需要在高温和高腐蚀的环境下长时服役,这就需要单晶涡轮叶片具有优异的高温力学性能、较高的抗氧化和抗腐蚀性能,而镍基单晶高温合金作为航空发动机涡轮叶片的首选材料,近几十年来一直受到研究者的关注。为进一步提高先进镍基高温合金的承温能力,需不断提高先进镍基单晶高温合金中难熔元素(例如Re和W)的含量。同时,铸态镍基单晶高温合金中存在成分不均匀(严重的显微偏析)和组织不均匀(大量的枝晶间析出物)的缺陷,这种成分和组织的不均匀性如果不能被高温固溶处理消除,则将显著恶化单晶高温合金的力学性能与长时服役性能。因此,有必要探索适用于先进镍基单晶高温合金的固溶处理工艺。固溶处理工艺的发展可以分为两个阶段。第一阶段:第一代单晶高温合金,由于合金中不含Re元素,合金只需要在γ'回溶温度和初熔温度之间保温较短的时间即可实现合金组织和成分的均匀化。第二阶段:从第二代单晶高温合金开始,合金中难熔元素(尤其是Re元素)的含量不断增加,合金的成分均匀化难度显著增大,即固溶温度显著升高、固溶时间显著延长。因此,先进镍基单晶高温合金固溶处理工艺的研究重点从关注合金中各相的溶解温度和合金的初熔温度转变为合金中各元素的均匀化程度。大量的研究结果表明,低温段固溶的目的是通过固态相变的方式消除枝晶间析出物,而高温段固溶的目的是通过固相扩散的方式消除或降低合金元素的显微偏析。随着单晶高温合金的发展,先进单晶高温合金中难熔元素(例如Re和W)的含量显著提高,一方面,难熔合金元素在Ni中具有较低的互扩散系数;另一方面,难熔元素在铸态单晶高温合金中的显微偏析程度较高。因此对于先进镍基单晶高温合金,实现元素均匀化和制定合理的固溶处理工艺的难度显著提高。同时,单晶高温合金的相变温度也受到固溶处理工艺的影响。本文归纳总结了单晶高温合金固溶处理制度的研究进展,详细介绍了第二代和第三代镍基单晶高温合金的固溶处理制度,阐述了固溶处理对显微组织和成分分布的影响规律,对比了单晶高温合金传统的台阶式升温固溶处理工艺和新型的连续升温固溶处理工艺,并对重熔固溶处理工艺进行了介绍。     

浇注温度对DD6单晶高温合金凝固组织的影响

研究了浇注温度对第二代单晶高温合金DD6凝固组织的影响.结果表明,随着浇注温度的降低,DD6合金的一次枝晶间距稍有增加,枝晶干与枝晶间γ′相尺寸略有增大,γ-γ′共晶相尺寸增加,共晶含量略有减少,合金中主要元素偏析明显减轻.     

复杂镍基单晶铸件显微孔洞的形成机理EI北大核心CSCD

采用高分辨透射X射线三维成像技术研究高速凝固法(high rate solidification,HRS)制备的3种成分复杂单晶铸件叶身和缘板部位的铸态显微孔洞分布情况。结果表明:凝固温度范围和枝晶排列曲折程度对孔洞的影响很大。铸件叶身部位,不同成分单晶的枝晶排列方式相同。其中,一代单晶的凝固温度范围最大,其孔洞体积分数也最大。二代单晶和三代单晶的凝固范围差异不大,孔洞体积分数主要受共晶体积分数的影响。随着单晶代次的增加,合金中难熔元素的含量将会增加,继而引起叶身部位共晶体积分数的增加。因此,合金最后凝固阶段枝晶间的空隙尺寸增加,液相压降降低,导致形成孔洞的体积分数减小。相比于叶身部位,缘板部位的孔洞主要由枝晶曲折程度决定。一代单晶缘板部位的枝晶曲折程度变化不明显,其孔洞体积分数与叶身部位的孔洞体积分数差异不大。二代单晶和三代单晶缘板部位的枝晶曲折程度逐渐增加,其孔洞体积分数增加。     

钌和铼对先进单晶高温合金组织稳定性的协同影响

为研究高代单晶高温合金组织稳定性影响机制,制备含6%(质量分数,下同)Ru和4.5%Ru的两种单晶高温合金D1和D2,经完全热处理后在980℃下长期时效1000 h。观察不同尺度上的显微组织及合金元素分布,并结合热力学计算进行分析。结果表明:两种合金经完全热处理后仍有较高含量的高熔点合金元素偏析于枝晶干中,使枝晶干区域长期时效后均有较多TCP相析出;两种合金中,Ru和Re均为TCP相主要形成元素,Ru含量较高的D1合金中TCP相析出量多于Ru含量较低的D2合金;Ru和Re含量增加会使合金平均d轨道电子能级增大,增加合金TCP相析出倾向,但由于Ru可以降低Re在γ相中偏析程度,因此Ru含量增加又可以减少Re对合金组织稳定性的不良影响;在本研究中,Ru对TCP相析出的促进更为显著,因此,在980℃下长期时效1000 h后D1合金较D2合金析出更多TCP相。     

强制对流作用下多枝晶生长的相场法研究

采用耦合溶质场、温度场和流场的相场模型,对Ni-Cu合金凝固过程中多枝晶生长进行模拟,研究了多枝晶生长形貌及温度场和溶质场分布.结果表明:熔体流动显著改变凝固前沿的传热和传质,从而影响枝晶生长.受过冷熔体冲刷,枝晶逆流侧前沿溶质浓度和温度低,枝晶臂尖端生长迅速;枝晶顺流侧前沿溶质浓度和温度高,枝晶臂尖端生长缓慢.在熔体...     

单晶高温合金激光表面快速凝固组织的研究

本文研究一种抗热腐蚀单晶镍基高温合金的激光表面快速凝固组织。结果表明:快速凝固组织为沿<001>方向择优生长、整齐排列的极细小的胞、枝晶组织;胞、枝晶间距随激光束移动速度的增加而显著减小;快速凝固完全消除了枝晶间γ/γ’共晶与显微疏松;在胞、枝晶间区域发现MC碳化物(TiC)呈各种形态极为特殊的花状。     

重力对镍基单晶高温合金枝晶生长和微观偏析的影响

使用长50 m的落管研究Ni-Cr-Al-W-Ta镍基单晶高温合金在重力(1g)和微重力(μg)条件下的凝固行为。用金相显微镜(OM)观察合金的凝固组织并用图像分析软件测量和统计一次和二次枝晶间距,使用扫描电镜能谱(SEM-EDS)测定不同位置枝晶干与枝晶间的化学成分并计算微观偏析系数。结果表明,在重力和微重力条件下这种合金的枝晶特征和合金元素的微观偏析明显不同。重力样品一次和二次枝晶间距比微重力样品的大,随着凝固距离的增大一次枝晶间距的差异变大,而二次枝晶间距的差距变化不大。随着凝固的进行,微重力样品枝晶间Ta、Cr和Al元素的含量呈现先明显升高后略微降低的趋势,W元素含量呈现逐渐下降的趋势,枝晶间液相的密度呈现略微降低的趋势。重力样品枝晶间Ta、Cr和Al元素含量的分布趋势与微重力样品基本相似,W元素含量的分布则与微重力样品明显不同,大部分凝固阶段呈上升趋势,使枝晶间液相的密度沿逆重力方向提高。上述结果表明,在重力条件下凝固前沿溶质密度差导致的对流作用微弱,不是造成枝晶间距增加的主要原因,主要原因应该与凝固前沿热对流造成的温度梯度的降低有关。     

镍基单晶高温合金DD403显微偏析

采用选晶法在改进型Bridgman定向凝固炉中制备镍基单晶高温合金DD403,利用电子探针(EPMA)技术研究了DD403合金在枝晶生长条件下的显微偏析。结果表明,随着抽拉速率增加DD403的偏析程度逐渐加剧。偏析于枝晶间元素Al、Ti和枝晶干元素Co、W的偏析程度随着抽拉速率的增加而增大,而合金元素Mo和Cr的偏析比接近于1,基本不存在偏析,且偏析比随抽拉速率增加没有明显变化。研究结果同时表明,随着抽拉速率增加DD403的共晶含量逐渐增加。     

抽拉速率对DD6单晶高温合金组织的影响

采用不同的抽拉工艺制备DD6单晶合金,分析了DD6单晶合金的显微组织,研究了不同抽拉工艺对DD6合金组织的影响.结果表明,随着抽拉速率的降低,DD6合金一次枝晶间距增加,枝晶干和枝晶间γ′相尺寸变大,共晶组织呈粗化趋势,γ-γ′共晶组织含量减少,合金中主要元素偏析程度减轻.     

单晶高温合金的研究进展

本文介绍了单晶高温合金的成分设计、制取工艺以及显微组织与性能间关系的最新研究进展。指出在设计单晶高温合金成分时,应充分考虑合金的工艺性能,综合考虑合金元素的作用,发展专项用途的单晶高温合金。籽晶法比选晶法能更准确地控制铸件的晶体取向,应大力发展高梯度定向凝固炉,同时发展高效高纯的熔化方式。初始γ′粒子为立方体状并定向排列时,往往具有优异的蠕变性能;负的晶格错配度越大,蠕变性能越好;单晶高温合金是高度各向异性的;显微疏松、夹杂显著影响单晶高温合金的性能。     

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.     

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.     

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.