Ni基高温合金真空感应熔炼脱硫

研究了使用CaO坩埚真空感应熔炼炼Ni基高温合金过程中的脱硫情况;分析了加Al的脱硫作用;结合坩埚壁的XRD分析和成分分析数据讨论了CaO坩埚脱硫机理;对CaO坩埚内壁表面发生的化学反应进行了初步热力学计算和讨论.     

夹杂物在P/M镍基高温合金中的变形行为及对低周疲劳性能的影响

通过在 5 0～ 10 0 μm粒度范围FGH95合金粉末中预先加入夹杂物的方法 ,系统研究了5 0～ 5 0 0 μm有机和无机不同类型的夹杂物 ,经过热等静压和热等静压加锻造后的形态变化 ,及其与合金基体的相互作用特点 ,以及对P/M盘件径向试样低周疲劳寿命的影响。     

The effect of random grain distributions on fatigue crack initiation in a notched coarse grained superalloy specimen

Coarse grained superalloys are of large interest in high temperature applications, and can be found in e.g. gas turbine components, where great care must be given with respect to high temperature fatigue. Due to the large grain size, the material behaviour at e.g. sharp notches cannot be considered homogeneous. As a consequence, the fatigue behaviour is likely to expose a large variation. In order to numerically investigate this variation, a Monte Carlo analysis has been carried out by 100 FE-simulations of notched specimens, where placements and orientations of the grains were randomised. Furthermore, each grain was modelled as a unique single-crystal, displaying both anisotropic elastic and plastic behaviour and tension/compression asymmetry. The effect of randomness was investigated by the obtained dispersion in fatigue crack initiation life. It was concluded that the fatigue life behaviour of coarse grained nickel-base superalloys may show a considerable variation, which cannot be captured by one single deterministic analysis based on data for a homogenised material. Furthermore, the dispersion is of such a magnitude that it needs to be taken into account in industrial applications where highly stressed coarse grained materials are used.     

Evolution of microstructure and properties of internal nitride dispersion strengthened alloy before nitriding

Internal nitride dispersion strengthened superalloy is a new type of high performance superalloy for combustion chamber. The background and development of this alloy were firstly introduced. And then the microstructure and properties of NS163 which is a typical internal nitride dispersion strengthened alloy were investigated. The results show that the microstructure of NS163 is simple in the temperature range of 900??1250??, which is composed of austenite matrix and MC carbide. The recrystallization behavior of the cold- rolled sheet under the test condition was studied systematically. It is found that the solid solution temperature of the finished product should be 1200??, and after solid solution at 1200??, the sheet has 5 grade average grain size, excellent cold workability and low tensile strength at high temperature. The above results can help to optimize the microstructure of NS163 alloy sheet before nitriding and provide a basis for the evaluation of the strengthening effect of the alloy after internal nitriding.     

Grain size effect on cyclic deformation behavior and springback prediction of Ni-based superalloy foil

In order to clarify the influence of grain size on cyclic deformation response of superalloy sheets and springback behavior, cyclic loading–unloading and shearing tests were performed on the superalloy foils with 0.2 mm in thickness and diverse grain sizes. The results show that, the decline ratio of elastic modulus is weakened with increasing grain size, and the Bauschinger effect becomes evident with decreasing grain size. Meanwhile, U-bending test results determine that the springback is diminished with increasing grain size. The Chaboche, Anisotropic Nonlinear Kinematic (ANK) and Yoshida-Uemori (Y-U) models were utilized to fit the shear stress–strain curves of specimens. It is found that Y-U model is sufficient of predicting the springback. However, the prediction accuracy is degraded with increasing grain size.     

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.     

Effect of long time service exposure on microstructure and mechanical properties of gas turbine vanes made of IN939 alloy

In the present study, the effects of long-term service exposure have been investigated on microstructure and mechanical properties of gas turbine vanes made of IN939 superalloy. The major microstructural changes for the investigated service-exposed vanes include the formation of continuous grain boundary carbides and the transformation (degeneration) of MC carbides located at the grain boundaries. The brittle σ phase, which is predicted to be stable on the basis of thermodynamic calculations, is not observed in the microstructure of service-exposed vanes. The microstructural changes during service lead to a loss in room temperature ductility as well as in creep properties of the alloy.     

铸造镍基高温合金增材修复技术的研究现状

铸造镍基高温合金广泛用于燃气轮机与航空发动机叶片等高温部件,长时间运行过程中经常发生叶片局部损伤失效,其维修或更换成本极高。通过增材修复来恢复局部损伤叶片的性能,将极大地降低制造成本、缩短制造周期、节约资源,具有极大的社会效益和市场价值。本文针对燃气轮机与航空发动机用铸造镍基高温合金部件的服役工况与失效形式,结合铸造镍基高温合金的成分、组织与性能特点,系统分析了增材修复时出现裂纹的类型、特点及形成机理,阐述了各类裂纹的主要影响因素,从增材工艺和材料两方面分类综述了减少或避免裂纹的增材修复工艺与技术现状,分析了不同增材修复方法的优缺点与未来可能的研究热点。     

Room temperature tensile deformation behavior of a Ni-based superalloy with high W content

K416B Ni-based superalloy with high W content has good high temperature properties and low cost, which has a great development potential. To investigate the room temperature tensile property and the deformation feature of K416B superalloy, tensile testing at room temperature was carried out, and optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to analyze the deformation and damage mechanisms. Results show that the main room temperature tensile deformation features of the K416B nickel-based superalloy are dislocations slipping in the matrix and shearing into γ′ phase. The <110> super-dislocations shearing into γ′ phase can form the anti-phase boundary two coupled (a/2)<110> partial-dislocations or decompose into the configuration of two (a/3)<112> partial dislocations plus stacking fault. In the later stage of tensile testing, the slip-lines with different orientations are activated in the grain, causing the stress concentration in the regions of block carbide or the porosity, and cracks initiate and propagate along these regions.