定向凝固和单晶高温合金及涡轮叶片的发展

北京航空材料研究所对定向凝固及单晶高温合金及工艺进行了多年卓有成效的研究,建立了先进的定向凝固设备,发展了定向凝固工艺,研制了一系列高性能定向和单晶高温合金;对合金设计、热处理、合金元素的作用进行了分析研究,为确定合适的化学成分及选定最佳工艺参数提供了可靠的基础;进行了精密铸造工艺的研究,发展了无余量铸造技术和用于定向及单晶的陶瓷型壳和型芯,并用此发展了多种航空定向和单晶叶片,特别是研制和批生产了用于先进航空发动机的DZ22无余量具有复杂内冷通道的空心涡轮叶片。现在,其主要目标是研制无余量的单晶空心叶片及其他单晶课题。     

单晶高温合金定向凝固过程数值模拟

实测了不同抽拉速度单晶高温定向凝固过程的初始条件,边界条件及温度场,建立了数值模拟系统的实体模型,采用ＰｒｏＣＡＳＴ有限元模拟软件包计算了不同抽拉速度单晶合金试板的定向凝固过程温度场。     

DD6单晶高温合金导向叶片定向凝固过程数值模拟

建立涡轮导向叶片三维实体模型,采用有限元软件ProCAST对DD6单晶高温合金导向叶片凝固过程温度场进行数值模拟;测试DD6单晶高温合金导向叶片不同位置凝固过程的温度变化.结果表明:数值模拟结果与实测结果偏差小于5％,吻合良好;导向叶片叶身的温度梯度大部分保持在25～45℃/cm范围内,缘板处温度梯度约为35℃/cm,...     

镍基单晶高温合金涡轮叶片缘板杂晶的研究进展

镍基单晶高温合金涡轮叶片缘板杂晶的出现严重影响叶片的力学性能,导致叶片报废。综述了关于缘板杂晶的形成本质的研究,总结了不同影响因素对缘板杂晶形成的影响及原因并概况了几种不同杂晶的控制方法,指出了以往研究中存在的问题,展望了未来研究的方向。     

镍基单晶高温合金定向凝固的数值模拟

概述了目前国内外镍基单晶高温合金定向凝固数值模拟的研究进展,定向凝固过程的数值模拟由宏观向微观转变,详细介绍了微观组织数值模拟的几种主要方法：决定论方法、随机论方法和相场方法,评述了这几种方法的特点以及局限性,指出宏观和微观现象的完整耦合可以对镍基单晶高温合金凝固过程做出更加准确的模拟预测。     

非定向熔模铸造过程中高温合金叶片晶粒组织的计算机模拟

论述了近年来发展起来的非定向凝固高温合金叶片熔模铸造过程中晶粒组织形成的计算机模拟方法，包括凝固过程中晶粒组织形成的物理模型，模拟中所采用的二维和三维胞状自动机（CA）技术。     

数值模拟在单晶高温合金熔模铸造中的应用

由于单晶高温合金消除了晶界这一高温薄弱结构,已成为航空发动机首选的热端部件材料。为了满足航空发动机对推重比和涡轮燃气温度的更高需求,新型单晶高温合金中添加了越来越多的Re、Ru等难熔元素,致使单晶制备过程中缺陷形成倾向显著提高,研制周期和研制成本明显增加,严重限制了单晶高温合金的产业化应用。近年来,随着计算方法和熔模铸造技术的发展,数值模拟在单晶高温合金制备领域中得到了越来越广泛的应用,已成为减少单晶铸造缺陷,获得高质量单晶铸件的重要手段。以商用铸造模拟软件Procast为例,对单晶高温合金定向凝固过程的温度场分布和组织演化进行了分析,综述了数值模拟在单晶熔模铸造研究中的应用现状。首先,介绍了数值模拟中的前处理过程,即几何建模、网格划分等,强调了前处理过程的注意事项。随后,根据已有文献,分析了数值模拟技术在研究温度场和晶粒组织演化过程的作用。最后,指出数值模拟技术在单晶高温合金熔模铸造领域进一步发展需要解决的问题。     

镍基单晶高温合金定向凝固的数值模拟

概述了目前国内外镍基单晶高温合金定向凝固数值模拟的研究进展,定向凝固过程的数值模拟由宏观向微观转变,详细介绍了微观组织数值模拟的几种主要方法:决定论方法、随机论方法和相场方法,评述了这几种方法的特点以及局限性,指出宏观和微观现象的完整耦合可以对镍基单晶高温合金凝固过程做出更加准确的模拟预测。     

DD3单晶合金的评估

叙述了北京航空材料研究院和美国普拉特惠特尼公司对ＤＤ３单晶合金的成本，主要力学性能指标和单晶铸性能进行的评估。评估认为：ＤＤ３合金有优良的力学性能和良好的铸造性能性能，     

镍基单晶高温合金涡轮叶片缘板杂晶的研究进展

镍基单晶高温合金涡轮叶片缘板杂晶的出现严重影响叶片的力学性能,导致叶片报废.综述了关于缘板杂晶的形成本质的研究,总结了不同影响因素对缘板杂晶形成的影响及原因并概况了几种不同杂晶的控制方法,指出了以往研究中存在的问题,展望了未来研究的方向.     

两种型壳温度对DD9单晶涡轮叶片凝固组织的影响EI北大核心CSCD

为了研究1500℃和1540℃两种型壳温度对第三代单晶高温合金DD9叶片截面凝固组织的影响,采用光学显微镜、扫描电子显微镜对叶片典型截面凝固组织进行分析。结果表明:随着型壳温度的增加,DD9单晶涡轮叶片凝固组织的枝晶花样呈细小趋势,二次枝晶呈发达趋势。相同型壳温度下,叶片叶身部位的枝晶比榫头部位的枝晶更细小。随着型壳温度的增加,枝晶干和枝晶间的γ′析出相尺寸和分散度均减小,并且γ′析出相尺寸分布遵循正态分布规律。相较枝晶间区域,枝晶干区域的γ′析出相的平均尺寸减小了61%。相同型壳温度下,叶片叶身部位的γ′析出相尺寸比榫头部位的γ′析出相尺寸更细小。与截面积变小相比,提高型壳温度会使γ′析出相变小更显著。随着型壳温度的增加,γ-γ′共晶尺寸和含量减小,γ-γ′共晶组织呈葵花状和光板状两种形貌特征。     

基于不同原始组织预设变形第四代单晶高温合金的再结晶行为

第四代单晶高温合金标准热处理试样和铸态试样压痕后分别在1100,1150,1200,1250,1300℃和1340℃退火处理,采用光学显微镜、扫描电镜、电子背散射仪研究不同条件的再结晶组织。结果表明:1100,1150,1200℃退火处理后,标准热处理试样和铸态试样都出现胞状再结晶。1250℃退火处理后,标准热处理试样和铸态试样都为混合再结晶。1300℃退火处理后,标准热处理试样再结晶组织全部为等轴再结晶,而铸态试样仍为混合再结晶。1340℃退火处理后,标准热处理试样和铸态试样都形成了等轴再结晶。随着退火温度升高,标准热处理试样和铸态试样的再结晶层深度明显增加,标准热处理试样再结晶深度明显大于铸态试样,相同条件下标准热处理试样的再结晶晶粒更容易长大。再结晶与基体的界面为小角度晶界、大角度晶界,而再结晶晶粒之间为小角度晶界、大角度晶界和孪晶界。孪晶在单晶高温合金再结晶的过程中发挥了重要作用。     

Study on the preparation and microstructure of a single-crystal hollow turbine blade

This paper studied the structural design of a ceramic core and a blade, ceramic core localization, shell preparation, casting process, core leaching technology, and the heat treatment process of a single-crystal hollow turbine blade. The results show that the single-crystal structure solidification sequence of the blade platform is consistent with the cooling sequence and the pulling-out direction of the blade. The primary dendrites were obviously enlarged with the increase of the blade thickness owing to the change in the local cooling rate. Besides, the γ′ phase had a high uniform size distribution ranging from 0.40 to 0.60?µm after heat treatment, and the cubic degree was more homogeneous in comparison with the as-cast microstructure, which are favorable for the superalloy structure. Moreover, γ′ phase size gradually increased and its quantity gradually reduced owing to the increase of the wall thickness in the growth direction.     

Process modelling of grain selection during the solidification of single crystal superalloy castings

A process model is described for the grain selection occurring during the solidification of single crystal investment castings, which are now used widely for a number of critical applications in gas turbine engines. The basis of the model is a thermal analysis of the heat transfer in the vicinity of the chill region onto which the molten metal is poured. Subsequently the competitive growth of grains during directional solidification is simulated via a cellular-automaton technique. For the purpose of model validation, processing trials have been carried out on a commercial single crystal casting furnace. The thermal cycles set up in and around the vicinity of the grain selector have been measured, and these are used to choose a number of critical parameters in the thermal model. The evolution of grain structure during competitive growth has been characterised using a number of analytical techniques, including orientation imaging microscopy. The results are compared critically with the predictions from the model. It is shown that the model is able to reproduce the statistical distribution describing the final casting orientation, measured with respect to the 001 crystallographic pole. The model is used to study the geometrical factors influencing competitive growth and the efficacy of two designs of grain selector, and in particular the conferral of any control of the secondary 001 orientation.     

The influence of crystal orientations on fatigue life of single crystal cooled turbine blade

A method based on the orthotropic elastic finite element analysis (FEA) has been presented to analyze the fatigue life of cooled turbine blades made of nickel-based single crystal superalloy (SC). Special attention was put on the influence of the crystallographic orientations on the strength and fatigue life of SC cooled turbine blades. It is shown that, due to the influence of the temperature distribution and complexity of cooling tunnel, the place of the maximum resolved shear stress in the blade is not corresponding to the most dangerous place, where results in the minimum fatigue life. For the SC cooled turbine blades studied in the paper, as the same of the most commercial SC blades in the world market, the axial direction is cast to [0 0 1] crystallographic orientation within 15° deviation, and the other two directions are in random. It is found that the randomness of the two directions has only limited influence on the distributions of Mises stress and the maximum resolved shear stress in the blade. But the deviation of the axial direction of the blade has obvious influence on the stress distribution, and the influence of the deviation and randomness orientations on the fatigue life is also obvious. Finally, the benefit of the optimization of the crystallographic orientations of SC cooled turbine blades on the fatigue life is highlighted.     

镍基单晶合金CMSX-6的再结晶行为及热裂倾向

在不同热处理温度和载荷下,研究了CMSX-6单晶的再结晶现象。结果表明:在低于1 150℃×4 h热处理后,没发现再结晶现象,但在载荷的作用下,单晶退火时γ'相形成元素自发偏析,造成大量的大颗粒γ'相在共晶周围析出;随着热处理温度升高,载荷影响区再结晶经历由压痕周围胞状再结晶、枝晶干再结晶、多个等轴再结晶三个阶段;在高于1 150℃×4 h热处理时,单晶随着载荷的增加,再结晶的范围和深度明显增大;以及随冷却速率的增加,再结晶晶粒之间的热裂倾向增大,致使大量热裂沿晶界分布。     

检验腐蚀对镍基单晶高温合金高周疲劳性能的影响EI北大核心CSCD

为了研究检验腐蚀对一种镍基单晶高温合金高周疲劳性能的影响,将经过标准热处理的试样置于FeCl 3+HCl+H 2O腐蚀剂中分别腐蚀2次和4次,采用莱卡DCM8共聚焦显微镜和扫描电镜对未腐蚀、2次与4次腐蚀试样的表面形貌进行观察,然后分别测试未腐蚀和4次腐蚀试样760℃与980℃的旋转弯曲疲劳性能。结果表明:未腐蚀试样表面存在纵向且相互平行的由抛光带来的细小抛痕,表面粗糙度低;2次腐蚀后,表面抛痕有所减少,枝晶间区域出现腐蚀坑,表面粗糙度增加;4次腐蚀后,表面抛痕被完全腐蚀掉,腐蚀坑深度和表面粗糙度进一步增加。4次腐蚀会略微降低合金760℃的疲劳性能,但对高应力幅条件下的疲劳寿命影响较大,对低应力幅条件下的疲劳寿命影响较小。4次腐蚀对合金980℃疲劳性能影响很小。     

Low cycle fatigue modeling for nickel-based single crystal superalloy

The low cycle fatigue (LCF) characteristics of nickel-based single crystal (SC) superalloy have been experimentally and numerically investigated. The effects of crystallographic orientation, load ratio and stress concentration are studied. In order to model the effect of crystallographic orientation, a new orientation factor, which is relevant to the yield strength, is constructed. On the other hand, a new asymmetrical loading factor is introduced to describe the effect of load ratio. The LCF model for SC superalloy smooth specimen is established with these new damage parameters. The effect of the strain gradient on the LCF life of SC superalloy is further studied, which is applied to the evaluation of the LCF life of SC superalloy notched specimen. The LCF model proposed is validated by the experimental data of SC superalloy DD3 and PWA1480.     

The effect of material behaviour on the analysis of single crystal turbine blades: Part II – Component analysis

This paper describes the analysis of a turbine blade component using a slip system model developed for modern single‐crystal superalloys. Structural elasto‐viscoplastic calculations are carried out for the component. The emphasis throughout is on the effect of micromechanisms of deformation, accounted for in the material model, on the predicted overall behaviour of the component. With the recent proliferation in detailed material models that are available, it is prudent to take a step back and investigate the implications of such models for component analysis and design. This effect is manifested through the determination of a stabilised and redistributed stress state throughout the component. While some components are creep‐limited in design, many are fatigue‐limited and it is stabilised stresses which control the cyclic life of these components. The accuracy of the material model, incorporating various micromechanisms as a function of stress and temperature, can significantly effect these stabilised stresses. The effect of the crystallographic orientation on blade behaviour is illustrated and the implications of shakedown simulations for fatigue lifing of turbine blades are discussed.     

喷丸对DD6单晶高温合金拉伸性能的影响

采用扫描电子显微镜(SEM)、X射线(X-ray)和透射电子显微镜(TEM)等手段研究铸钢丸喷丸对第二代单晶高温合金DD6在500,600,650℃拉伸性能的影响。结果表明:500,600,650℃时,喷丸对DD6合金抗拉强度影响不大,略微提高屈服强度,显著降低伸长率和断面收缩率。喷丸DD6合金在流变应力上升到最高点后断裂,试样拉伸断裂后的横截面为圆形;未喷丸DD6合金拉伸曲线呈现双重阶段特征,试样拉伸断裂后的横截面为椭圆形。