The ternary Ni–Al–Co embedded-atom-method potential for γ/γ Ni-based single-crystal superalloys: Construction and application

An Ni-AI-Co system embedded-atom-method potential is constructed for the γ（Ni）/γ＇（Ni3A1） superalloy based on experiments and first-principles calculations. The stacking fault energies （SFEs） of the Ni（Co, A1） random solid solutions are calculated as a function of the concentrations of Co and A1. The calculated SFEs decrease with increasing concentrations of Co and A1, which is consistent with the experimental results. The embedding energy term in the present potential has an important influence on the SFEs of the random solid solutions. The cross-slip processes of a screw dislocation in homogenous Ni（Co） solid solutions are simulated using the present potential and the nudged elastic band method. The cross-slip activation energies increase with increasing Co concentration, which implies that the creep resistance of γ（Ni） may be improved by the addition of Co.

Numerical simulation on directional solidification and heat treatment processes of turbine blades

Study on turbine blades is crucial due to their critical role in ensuring the efficient and reliable operation of aircraft engines.Nickel-based single crystal superalloys are extensively used in the hot manufacturing of turbine blades due to their exceptional high-temperature mechanical properties.The hot manufacturing of single crystal blades involves directional solidification and heat treatment.Experimental manufacturing of these blades is time-consuming,capital-intensive,and often insufficient to meet industrial demands.Numerical simulation techniques have gained widespread acceptance in blade manufacturing research due to their low energy consumption,high efficiency,and rapid turnaround time.This article introduces the modeling and simulation of hot manufacturing in single crystal blades.The discussion outlines the prevalent mathematical models employed in numerical simulations related to blade hot manufacturing.It encapsulates the advancements in research concerning macro to micro-level numerical simulation techniques for directional solidification and heat treatment processes.Furthermore,potential future trajectories for the numerical simulation of single crystal blade hot manufacturing are also discussed.

Influence of platform position on stray grain nucleation in Ni-based single-crystal dummy blade clusters

Stray grains are the most severe of the solidification defects that occur in the industrial single-crystal blade preparation process.In this study,a single-crystal dummy blade cluster with different crystal orientations controlled by the seeding method was prepared,and the influence of the position of the circular platform(relative to the sample and furnace body)on stray grain nucleation was investigated.Results show that the microstructure of the circular platforms could be divided into the center,expansion,and stray grain regions.The inside of the circular platform facing the center of the cluster is more prone to stray grain formation than the outside of the circular platform facing the furnace body.With an increase in the distance between the circular platform and the bottom of the dummy blade cluster,the stray grain region expands,whereas the expansion region narrows.The stray grain is slightly aggravated with increase of the misorientation.Finally,the mechanism underlying the influence of platform position on the formation of stray grains in single-crystal dummy blade clusters is discussed based on the temperature evolution during directional solidification.

Growth of Casting Microcrack and Micropore in Single-crystal Superalloys Analysed by Three-Dimensional Unit Cell

Finite element （FE） analysis was employed to investigate the casting microcrack and micropore growth in nickel-base single-crystal superalloys DD3. Based on the finite deformation rate-dependent crystallographic constitutive equation, the simulations of casting microcrack and micropore growth in three-dimensional unit cell model were carried out in a range of parameters including stress triaxiality, Lode parameter and type of activated slip systems. The FE results show that the stress triaxiality has profound effects on growth behavior, and the Lode parameter is also important for the casting microcrack and micropore growth. The type of operative slip systems has remarkable effect on casting microcrack and micropore growth, so the life of single- crystal component is associated with the type of activated slip systems, which is related to Schmid factor and the number of activated slip systems. The growth comparison between microcrack and micropore reveals that when the material is subjected to large deformation, the growth rate of microcrack is faster than that of micropore, i.e. microcrack is more dangerous than micropore; the microcrack is easier to result in brittle fracture than micropore. The stress triaxiality and Lode parameter have strong influence on the growth of microcrack and micropore.

Dynamic recrystallization of single-crystal nickel-based superalloy

The dynamic recrystallization behavior of single-crystal（SC） superalloy SR.R99 at low strain rate was investigated by high-temperature creep testing.The results show that dynamic recrystallization may take place after the uncoated samples have been creep-tested in air at high temperature and low stress for a long time.Both the threshold temperature and strain for the dynamic recrystallization of SC superalloy SRR99 at low strain rate are lower than those for the static recrystallization.Dynamically recrystallized grains with the depth less than 15 μm are only located in the surface γ＇-free layers,and the recrystallized grains are well-developed grains without columnar y＇precipitates within them.The dynamic recrystallization behavior of SC superalloy SRR99 at low strain rate is mainly related to high-temperature oxidation.Suitable protective coating can effectively prevent the dynamic recrystallization of SC superalloy components in service.In addition,the dynamic recrystallization behavior of SC superalloy SRR99 at high strain rate was also studied by high-temperature compression testing.At high strain rate,a higher temperature and larger strain are needed for the occurrence of dynamic recrystallization than at low strain rate,and the recrystallized grains have cellular structures with an amount of columnar γ＇ precipitates within them.

Evolution mechanism of crystallographic orientation in grain continuator bars of a Ni-based single-crystal superalloy prepared by Bridgman technology during directional solidification

Single-crystal rods with different diameters and deviation angles with respect to the solidification direction were produced by Bridgman rapid solidification method at withdrawal rates of 3 and 6 mm·min^(-1) and used as grain continuators.The crystallographic orientation of the rods,which cross-sections were perpendicular to the solidification direction at different solidification heights,was measured by electron backscattered diffraction,while the corresponding microstructures were observed by optical microscopy.The mushy zone morphology and the distribution of the temperature gradient were simulated by the finite element analysis software ProCAST.The experimental results indicate that the crystallographic orientation of the single-crystal rods corresponds to the statistical average value of all the dendrite orientations in cross-section.The crystallographic orientation of the primary and secondary dendrites of each single-crystal rod at different cross-sections fluctuates irregularly within a small range(less than 4°).The crystallographic orientation of the dendrite in each single-crystal rod is not exactly consistent with each other and is affected by their branching mode of dendrites in the solidification space.In addition,the simulation results show that the mushy zone shapes and the temperature gradient of single-crystal rods change with the increase of solidification height during the solidification process.Finally,the evolution mechanism of the crystallographic orientations and the corresponding influence factors were analyzed and discussed.

R & D OF CAST SUPERALLOYS AND PROCESSING FOR GAS TURBINE BLADES IN BIAM

Research and development of cast superalloys and processing for turbine blades in BIAM during the last 35 years have been reviewed briefly in this paper.

Molecular dynamics study of mosaic structure in the Ni-based single-crystal superalloy

The mosaic structure in a Ni-based single-crystal superalloy is simulated by molecular dynamics using a potential employed in a modified analytic embedded atom method. From the calculated results we find that a closed threedimensional misfit dislocation network, with index of （011）{100} and the side length of the mesh 89.6A, is formed around a cuboidal γ′ precipitate. Comparing the simulation results of the different mosaic models, we find that the side length of the mesh only depends on the lattice parameters of the γ and γ′ phases as well as the γ/γ′ interface direction, but is independent of the size and number of the cuboidal γ′ precipitate. The density of dislocations is inversely proportional to the size of the cuboidal γ′ precipitate, i.e. the amount of the dislocation is proportional to the total area of the γ/γ′ interface, which may be used to explain the relation between the amount of the fine γ′ particles and the creep rupture life of the superalloy. In addition, the closed three-dimensional networks assembled with the misfit dislocations can play a significant role in improving the mechanical properties of superalloys.

Solidification Microstructures of a Single-crystal Superalloy under Ultra-high Temperature Gradient Conditions

The solidification microstructures and solute segregation of a newly developed hot corrosion resistant single-crystal Ni-base superalloy were investigated with a zone-melting and ultra-high thermal gradient unidirectional solidification apparatus.Compared with the microstructures solidified at conventional low thermal gradient conditions,the dendrite arm spacings,the interdendritic microporosity and γ/γ' eutectic,and the severity of solute segregation of the single-crystal superalloy solidified at ultra-high thermal gradient conditions were considerably reduced.It was shown that the microstructure solidified under ultra-high thermal gradient condition is ideal for the full exploitation of the excellent property potentials of single-crystal superalloys.

Discontinuous Precipitation Reaction Front of Cellular Recrystallization for a Single-Crystal Superalloy Studied by Electron Microscopy

Combining analytical transmission electron microscopy systematic tilting, scanning transmission electron microscopy mapping and nano-beam electron diffraction operations, we obtain direct experimental proofs on the boundary type, elemental distribution and structure of the cellular reerystallization reaction front for a single- crystal superalloy. It is demonstrated that the cellular recrystallization reaction front usually corresponds to coincidence site lattice boundaries, and a thin layer of γ-forming elements such as Re, Cr, Mo and Co invariably exists in the direct reaction front. Furthermore, the thin layer with γ-forming elements is proved to be γ phase, with the same orientation as the neighboring original matrix.

氧化损伤对航空发动机涡轮叶片裂纹扩展影响

氧化损伤以及裂纹在涡轮叶片服役过程中不可避免,对裂纹行为的预测及其受氧化损伤的影响对于服役安全和寿命管理具有重要意义。针对航空发动机高压涡轮叶片长期处于高温环境下产生的氧化损伤以及裂纹问题,通过对紧凑拉伸(CT)试样在850℃条件下进行疲劳裂纹扩展试验,得到正常试样和氧化损伤后试样的疲劳裂纹扩展速率;运用Paris模型考虑了存在氧化损伤时裂纹扩展的情况,对比氧化损伤对疲劳裂纹扩展速率的影响。本文以某航空发动机高压涡轮叶片为例,聚焦于氧化损伤对裂纹扩展阶段的影响,利用ANSYS和Franc3D软件分析并对比涡轮叶片在有无氧化损伤条件下的裂纹扩展寿命。结果表明,叶片前缘裂纹受氧化损伤影响下,其循环寿命平均降低到无氧化损伤情况下的44.02%,叶片后缘裂纹循环寿命平均降低到无氧化损伤情况下的50.22%。对实际服役环境工作条件下的涡轮叶片寿命评估提供基础参考,以及在其他实际工程中正确评价材料、预测工程热端零部件的使用寿命和设计强度均有重要的现实意义。

叶片排列方式对一种第四代单晶高温合金叶片杂晶影响的数值模拟研究

针对组模生产第四代单晶高温合金叶片时由于温度场不均匀导致的缘板杂晶问题,采用有限元模拟软件ProCAST对叶片在组模中以不同方式排列时凝固过程的温度场和晶粒组织进行模拟计算,并且分析了添加引晶杆对杂晶的影响。结果表明,在组模生产时,由于中柱的保温作用小,导致横向温度场不均匀,叶片以0°排列时,缘板边角靠近中柱,其凝固过程中温度下降较快,会在边角形成大的过冷,同时凝固过程的温度梯度较小,枝晶生长慢,杂晶的形成倾向最大。随着排列角度的增加,横向温度场的不均匀性得到改善,但由于第四代合金形核过冷度小,在缘板位置都会有杂晶形成。添加引晶杆可以消除缘板杂晶,但对于叶片以0°排列时,由于叶片进气边靠近中柱,会在引晶杆内产生杂晶。叶片以90°排列时,横向温度场较为均匀,添加的引晶杆内不会产生杂晶,同时组模直径小,可以降低对炉体型腔的尺寸要求,有望成为生产高代次单晶叶片的最优排列方式。

钨极氩弧焊与激光熔覆修复的K403镍基高温合金导向器叶片组织与性能

K403镍基高温合金具有优异的室温和高温综合性能,广泛用于航空发动机涡轮叶片及导向器的制造。针对涡轮叶片长期服役于复杂工况产生的裂纹缺陷等问题,本工作先对钨极氩弧(tungsten inert gas,TIG)焊和激光熔覆两种工艺修复后的组织与拉伸性能展开对比分析,而后使用激光熔覆工艺修复叶片,并进行无损检测。利用OM、SEM观察微观组织、断口形貌,利用EDS进行相的成分分析。结果表明:TIG焊修复工艺在修复界面区附近易产生微裂纹缺陷,主要碳化物相和低熔点共晶组织引起;激光熔覆工艺修复区域的晶粒与组织更加均匀,微裂纹缺陷更易得到控制;激光熔覆工艺修复的试样综合力学性能明显高于TIG焊修复工艺的试样,且激光熔覆工艺具有较好的工艺稳定性,TIG焊修复工艺的室温拉伸强度为K403母材强度的69.22%,激光熔覆修复工艺室温抗拉强度达到了母材的87.44%,断口形貌显示修复区域的室温拉伸断口呈现出混合断裂特征,高温拉伸断口呈现出沿晶断裂的特征。修复区域的微裂纹、局部液相不足缺陷和碳化物是拉伸断裂的主要原因。激光熔覆修复工艺具有热源集中、热影响区小的优势,能够有效抑制修复区缺陷并细化微观组织,在叶片修复方面具有更大优势。使用激光熔覆修复工艺完成了叶片试车过程产生的边缘板裂纹损伤修复,经过荧光检测及煤油-白垩检测,满足相关使用要求。

Effect of Magnetic Field Configuration on Stray-Crystal Formation with Different Platform Sizes during Directional Solidification of Single-Crystal Superalloy

The magnetic field is an effective means to control the solidification structure and the defects of metal and semiconductor crystals.This work investigates the effects of Cusp magnetic field(CMF)and longitudinal magnetic field(LMF)on the stray-crystal formation in the platform regions during the directional solidification of single-crystal superalloy with the different cross section sizes.The application of CMF reduces the formation of platform stray-crystal,while LMF increases its generation.As the platform size increases,the stray-crystal ratio increases regardless of whether the magnetic fields are applied or not,the effectiveness of CMF increases,while that of LMF decreases.The reason that the effects of CMF and LMF on the platform stray-crystal formation could be attributed to the change of flow structure from the distribution characteristics of the thermoelectric magnetic force and the magnetic damping force near the liquid-solid interface.

面向单晶高温合金叶片的激光增材制造修复研究进展

镍基单晶高温合金因其卓越的高温性能,成为航空航天发动机及燃气轮机涡轮叶片的关键材料。复杂的服役环境常导致叶片损伤,但传统修复方法难以满足其对微观组织和力学性能的严格要求。激光增材制造技术作为一种先进的修复方法,能够在较小的热影响区内实现材料的高精度修复,展现出显著的技术优势。然而,激光增材制造技术修复单晶叶片仍面临如何保持单晶完整性、控制冶金缺陷、优化狭窄工艺窗口等问题。此外,激光增材制造修复后热处理制度仍不完善,热处理后产生的再结晶等缺陷会严重影响单晶高温合金叶片的持久、蠕变等力学性能。本文综述了激光增材制造修复镍基单晶高温合金叶片的研究进展,重点探讨了修复过程中裂纹、杂晶缺陷的控制,梳理了对修复后热处理制度的探索历程并总结了激光增材制造镍基单晶高温合金力学性能的相关研究。最后对未来研究方向和发展趋势进行了展望。

涡轮叶片材料CMSX-4超温状态组织演变研究

以涡轮叶片用材料CMSX-4合金为研究对象,采用体式显微镜、扫描电镜、维氏硬度计等研究了CMSX-4合金在超温状态下的组织演变以及硬度变化。结果表明:随温度升高,γ′相长大聚集的同时伴随着γ′相回溶,γ′相立方度下降,γ通道变宽。当超温处理温度到达1250℃时,γ/γ′相界面呈锯齿状;当温度达到1300℃后,γ′相全部回溶;当温度达到1350℃时,合金开始初熔,出现大量孔洞与γ+γ′共晶。当在1300℃以下一定温度保温时,随着保温时间的延长,γ′相百分含量逐渐减少并趋于稳定。当温度达到γ′相全部回溶温度时,因重新析出细小的二次γ′相,合金硬度显著升高,最高硬度达458 HV,比原始状态提高约12%。因此,对于过热等异常服役引起组织损伤与退化,可结合叶片宏观形貌、γ′相形态与百分含量、硬度退化情况进行材料损伤程度的评估。

Microstructure and creep properties of Ni-based single-crystal superalloys with Mo/Al addition at 760℃/850 MPa

The effect of Mo and Al addition on the microstructure as well as creep rupture properties at760.C/850 MPa was investigated by transmission electron microscopy(TEM)in a Ni-based single-crystal(SC)alloy with the composition of Ni-6.5Al-8.0Mo-2.4Cr-6.2Ta-4.9Co-1.5Re-(0.01-0.05)Y(wt%).The microstructure analysis shows that 0.5 wt%Al addition induces rapid decrease in creep rupture life,and this can be attributed to the formation of dense stacking faults cutting intoγ'precipitates,which can be explained by the increase in Orowan stress caused by the narrowerγchannel width and the decrease in stacking faults energy.Besides,1.5 wt%Mo addition increases the anti-phase boundary energy and decreases the stacking faults energy,resulting in fewer stacking faults and thus a slight decrease in the creep rupture life.

Study on Strength and Life of Anisotropic Single Crystal Blade - Part Ⅱ: Experimental Research

The single crystal blade is one of the key technologies for improving the performance, durability and reliability of aero-engines and ground gas-turbine engines. However, the anisotropic mechanical properties of the single crystal material makes a great deal of difficulties on the development and the application of the single crystal blade, which is a challenge for the engineering application of the single crystal superalloy and the theoretic bases of the application. Some researches on the strength analysis and the life prediction of the anisotropic single crystal blade were carried out by the authors' research team. They are as follows. The crystallographic constitutive models for the plastic and the creep behaviors and the method of the rupture life prediction were established and verified. The tensile or the creep experiments for DD3 single crystal alloy with different orientations under different temperatures and different tensile rates or under different temperatures and different stress levels were carried out. The experimental data and the anisotropic properties at intermediate and high temperatures revealed by the experiments are significant for the application of the single crystal alloy. In addition, the experimental research for a kind of single crystal blade was also made. As the application of the researches the strength analysis and the life prediction were carried out for the single crystal blade of a certain aeroengine. In this part, the experimental research work is describled, and the constitutive models and applications have been described in part I.

Multiscale modelling and simulation of single crystal superalloy turbine blade casting during directional solidification process

As the key parts of an aero-engine,single crystal(SX)superalloy turbine blades have been the focus of much attention.However,casting defects often occur during the manufacturing process of the SX turbine blades.Modeling and simulation technology can help to optimize the manufacturing process of SX blades.Multiscale coupled models were proposed and used to simulate the physical phenomena occurring during the directional solidification(DS)process.Coupled with heat transfer(macroscale)and grain growth(meso-scale),3D dendritic grain growth was calculated to show the competitive grain growth at micro-scale.SX grain selection behavior was studied by the simulation and experiments.The results show that the geometrical structure and technical parameters had strong influences on the grain selection effectiveness.Based on the coupled models,heat transfer,grain growth and microstructure evolution of a complex hollow SX blade were simulated.Both the simulated and experimental results show that the stray grain occurred at the platform of the SX blade when a constant withdrawal rate was used in manufacturing process.In order to avoid the formation of the stray crystal,the multi-scale coupled models and the withdrawal rate optimized technique were applied to the same SX turbine blade.The modeling results indicated that the optimized variable withdrawal rate can achieve SX blade castings with no stray grains,which was also proved by the experiments.

Numerical simulation on vacuum solution heat treatment and gas quenching process of a low rhenium-containing Ni-based single crystal turbine blade

Numerical heat-transfer and turbulent flow model for an industrial high-pressure gas quenching vacuum furnace was established to simulate the heating,holding and gas fan quenching of a low rhenium-bearing Ni-based single crystal turbine blade.The mesh of simplified furnace model was built using finite volume method and the boundary conditions were set up according to the practical process.Simulation results show that the turbine blade geometry and the mutual shielding among blades have significant influence on the uniformity of the temperature distribution.The temperature distribution at sharp corner,thin wall and corner part is higher than that at thick wall part of blade during heating,and the isotherms show a toroidal line to the center of thick wall.The temperature of sheltered units is lower than that of the remaining part of blade.When there is no shelteration among multiple blades,the temperature distribution for all blades is almost identical.The fluid velocity field,temperature field and cooling curves of the single and multiple turbine blades during gas fan quenching were also simulated.Modeling results indicate that the loading tray,free outlet and the location of turbine blades have important influences on the flow field.The high-speed gas flows out from the nozzle is divided by loading tray,and the free outlet enhanced the two vortex flow at the end of the furnace door.The closer the blade is to the exhaust outlet and the nozzle,the greater the flow velocity is and the more adequate the flow is.The blade geometry has an effect on the cooling for single blade and multiple blades during gas fan quenching,and the effects in double layers differs from that in single layer.For single blade,the cooing rate at thin-walled part is lower than that at thick-walled part,the cooling rate at sharp corner is greater than that at tenon and blade platform,and the temperature at regions close to the internal position is decreased more slowly than that close to the surface.For multiple blades in single layer,the temperature at sharp corner or thin wall in the blade that close to the nozzles is much lower,and the temperature distribution of blades is almost parallel.The cooling rate inside the air current channel is lower than that of at the position near blade platform and tenon,and the effect of blade location to the nozzles on the temperature field inside the blade is lower than that on the blade surface.For multiple blades in double layers,the flow velocity is low,and the flow is not uniform for blades in the second-layer due to the shielding of blades in the first-layer.the cooling rate of blades in the second-layer is lower than that in the first-layer.The cooling rate of blade close to the nozzles in the first-layer is the higher than that of blade away from the nozzles in the second-layer,and the temperature distribution on blades in the same layer is almost parallel.The cooling rate in thin wall position of blade away from the nozzles is larger than that in tenon of the blade closer to the nozzles in the same layer.The cooling rate for blades in the secondlayer is much lower both in thin wall and tenon for blades away from the nozzles.