Gamma prime and TCP phases and mechanical properties of thermally exposed nickel-base superalloy

The effect of long-term thermal exposure and casting superheat on microstructure, topologically close-packed (TCP) phases, γ?′ precipitation and mechanical properties of an experimental Ni-base superalloy were studied. The investigated alloys were produced by investment casting process under two levels of superheat. After solution heat treatment, at 1180°C for 2?h followed by air cooling; the two alloys under investigation were isothermally exposed at 845°C for 24, 200, 1000, and 1500?h. The long-term thermal exposure conditions have a significant impact on the precipitation and morphology of TCP and γ?′ phases. The σ phase precipitated as needle and platelet shapes, whereas the μ phase formed in plate and agglomerated shapes. The μ phase has high concentration of Cr, Mo, W, and Co, while the σ phase has high percentages of Ni and Ti. The μ phase was precipitated after thermal exposure of 200?h in the case of high superheat specimen and after 1000?h in low superheat specimen. The η phase found was also a thick plate-like shape in the microstructure of both alloys in the interdendritic zones. The optimum size and volume fraction of γ?′ precipitates were obtained after being thermally exposed for 200 and 1000?h for high and low superheat alloys, respectively. Consequently, the highest hardness level was achieved at the optimum conditions of γ?′ precipitates in high and low superheat alloys.     

Ti对镍基高温自润滑复合材料力学和摩擦学性能的影响

本文中采用热压烧结技术制备了镍基高温自润滑复合材料,研究了镍基合金基体中添加少量Ti对复合材料力学与高温摩擦学性能的影响.研究结果显示:两者的摩擦系数整体较低,添加少量Ti后,复合材料的硬度提高,室温弯曲强度明显降低,室温压缩强度基本不变,摩擦系数总体上略有降低,抗磨性能提高.摩擦机理方面,两者基本相同.     

K4169合金在人工海水中的腐蚀磨损图

采用恒电位测试方法研究了当载荷范围为5~20 N、电位范围为–0.6~0.3 V时镍基合金K4169/氧化铝陶瓷球摩擦副在人工海水中的腐蚀磨损行为,并根据试验数据获得了K4169合金的腐蚀磨损图(总损失图、磨损机理图和交互作用图).结果表明:K4169合金在室温下的人工海水中有良好的耐腐蚀性能,腐蚀速率为0.004 2 mm/a;磨损量Wc为总损失量T值的87.1%~96.8%,表明腐蚀磨损中K4169合金的损失以机械磨损为主,腐蚀损失量Cw很小.以ΔCw/ΔWc为判据可知:协同作用、加和作用和对抗作用均存在于K4169合金在人工海水的腐蚀磨损中.     

First principles study of the diffusional phenomena across the clean and Re-doped γ-Ni/γ'-Ni_3Al interface of Ni-based single crystal superalloy

Density functional theory calculations in conjunction with the climbing images nudged elastic band method are conducted to study the diffusion phenomena of the Ni-based single crystal superalloys.We focus our attention on the diffusion processes of the Ni and Al atoms in the γ and γ ' phases along the direction perpendicular to the interface.The diffusion mechanisms and the expressions of the diffusion coefficients are presented.The vacancy formation energies,the migration energies,and the activation energies for the diffusing Ni and Al atoms are estimated,and these quantities display the expected and clear transition zones in the vicinity of the interface of about 3–7(002) layers.The local density-of-states profiles of atoms in each(002) layer in the γ and γ ' phases and the partial density-of-states curves of Re and some of its nearest-neighbor atoms are also presented to explore the electronic effect of the diffusion behavior.     

Hot corrosion behavior of the spray-formed nickel-based superalloy

An investigation of low temperature hot corrosion is carried out on a spray-formed nickel-based superalloy FGH100pre-coated with Na_2SO_4~- NaCl at 700℃ for 100 h. Mass gain measurement, x-ray diffraction, scanning electron microscopy, and energy dispersive x-ray spectroscopy are used to study the corrosion behavior. Results reveal that corrosion behavior follows a sequence, that is, first rapidly proceeding, then gradually slowing down, and finally forming an outer layer composed of different types of oxides and an inner layer mainly comprised of sulfides. In-depth analysis reveals that the hot corrosion of FGH100 is a combined effect of oxidation-sulfidation and transfer of oxides.     

Effect of secondary orientation on notch-tip plasticity in superalloy single crystals

Numerical and experimental evolutions of slip fields in notched Ni-Base Single Crystal superalloy tensile specimens are presented as a function of secondary crystallographic orientation. The numerical predictions based on three-dimensional anisotropic elasticity and crystal plasticity are compared with experimental observations. The results illustrate the strong dependence of the slip patterns and the plastic zone size and shape on the secondary orientation of notches, which can have important consequences on crack initiation. Specific orientations or non-symmetric notch geometries lead to non-symmetric patterns on both sides of the sample. The computations show that strongly different plastic zones are expected in the core of the sample and at free surfaces. The ability of the anisotropic elastic model to anticipate the plastic domains, based on identifying dominant slip systems, is confirmed by the crystal plasticity computations, at low load levels. An important observation is that kink shear banding is a real deformation mode operating at crack tips and notches in high strength nickel-based single crystal superalloys for specific orientations.     

数字散斑相关法研究镍钴基高温合金中的PLC效应

作为航空发动机涡轮盘用新型材料,镍钴基变形高温合金在300～600℃温度区间内拉伸时会产生Portevin-Le Chatelier (PLC)效应.本文采用数字散斑相关方法,研究了镍钴基变形高温合金在400℃下拉伸变形过程中伴随PLC效应出现的应变局域化现象,即PLC带.实验结果表明,PLC带内的应变比试件平均应变大一个数量级,而带外部分应变接近于零.同时还观察到了带外部分的弹性收缩现象,即出现应变为负的区域.在拉伸全程中,PLC带与拉伸轴方向成约60°的夹角.PLC带的宽度均为4～4.5 mm,远大于试件最小尺寸(厚度),这一点与铝合金中的带宽与试件最小尺寸相近这一现象截然不同.     

基于微结构动态演化机制的单晶镍基高温合金晶体塑性本构及其有限元模拟

因其优异的高温力学性能,镍基单晶高温合金在航空航天和能源等领域得到了广泛的应用.镍基单晶高温合金优异的高温性能来源于其特有的两相微结构.基于代表体胞模型及分块均匀化方法,以位错密度为主要内变量,发展了一个包含两相微结构和位错演化信息的单晶镍基高温合金塑性行为的本构模型.该本构模型充分考虑了镍基单晶合金中位错在基体相和沉淀增强相中的多种演化机制,例如,基体位错八面体滑移、立方滑移、位错攀移、交滑移、位错弓出、位错切过沉淀增强相以及位错Kear-Wilsdolf(K-W)锁形成与解锁等.在商用有限元软件ABAQUS的框架下,编制了UMAT用户材料子程序.利用该用户子程序,对单晶和多晶镍基高温合金在不同温度、不同加载方向下的单调塑性、循环塑性、蠕变等典型行为进行了计算模拟.结果表明:该晶体塑性本构模型能"统一地"刻画镍基高温合金在不同温度、不同方向下的多种变形行为,并与实验结果具有良好的一致性.     

Effects of alloying element on stabilities,electronic structures,and mechanical properties of Pd-based superalloys

The thermodynamic stabilities, electronic structures, and mechanical properties of the Pd-based superalloys are studied by first principles calculations. In this work, we discuss the effect of Pd-based superalloys made from Al, Si, Sc, Ti,V, Cr, Mn, Fe, Cu, Zn, Y, Zr, Nb, Mo, Tc, Hf, Ta, W, Re, Os, Ir and Pt, and we also calculate a face centered cubic(fcc)structure 2 × 2 × 2 superalloy including 31 Pd atoms and one alloying element T M(Pd_(31)TM). The mixing energies of these Pd-Based superalloys are negative, indicating that all Pd-based superalloys are thermodynamically stable. The Pd_(31)Mn has the lowest mixing energy with a value of-0.97 eV/atom. The electronic structures of the Pd-based superalloys are also studied, the densities of states, elastic constants and moduli of the mechanical properties of the Pd-based superalloys are determined by the stress-strain method and Voigt–Reuss–Hill approximation. It is found that Pd_(31)TM is mechanically stable, and Pd_(31)Tc has the largest C_(11), with a value 279.7 GPa. The Pd_(31)Cr has the highest bulk modulus with a value of299.8 GPa. The Pd_(31)Fe has the largest shear modulus and Young's modulus with the values of 73.8 GPa and 195.2 GPa,respectively. By using the anisotropic index, the anisotropic mechanical properties of the Pd_(31)T M are discussed, and threedimensional(3 D) surface contours and the planar projections on(001) and(110) planes are also investigated by the Young modulus.     

单晶高温合金中铸造微孔洞的扩长

基于有限变形晶体塑性本构关系及轴对称体胞模型,采用有限元的方法,分析了在不同取向偏角及不同滑移系开动,单晶高温合金中铸造微孔洞扩长的力学行为。分析结果表明:取向偏角对铸造微孔洞的扩长具有重要的意义,但对铸造微孔洞的形状改变影响不大,为改善单晶高温合金热端部件的疲劳、蠕变性能,控制晶体的取向偏角是很必要的;滑移系族开动的类型对铸造微孔洞的扩长有很大的影响,这种影响与Schmid因子、加载的取向相关,为更加准确地分析单晶高温热端部件的寿命,确定滑移系族开动类型至关重要。