Innovative, massive gas turbines have emerged as critical equipment for achieving the goals of energy conservation and the development of new clean energy sources. As the inlet temperature of industrial gas turbines continues to rise, the high-temperature capabilities of hot corrosion-resistant single-crystal turbine blades should be enhanced. This work investigates the effects of Ta on the microstructural stability and creep properties of hot corrosion-resistant Ni-based single-crystal superalloys with varying Ta contents (2Ta, 5Ta, and 8Ta) during long-term thermal exposure at 900oC. The findings revealed that after various thermal exposure times, the addition of Ta had no observable influence on the size of γ' precipitates, but it considerably increased the cubic degree of γ' precipitates and continuously decreased the number of tertiary γ' precipitates in γ matrix. With the increase of Ta content from 2% to 5%, the volume fraction of γ' precipitates of 5Ta alloy is higher than that of 2Ta alloy except that which is close to each other when thermal exposure at 4000 h. In addition, the volume fraction of γ' precipitates increased was higher than that of 2Ta and 5Ta alloys, as the Ta content increased from 5% to 8% after various thermal exposure times. The creep lives of the three alloys at 900oC and 275 MPa exhibited different trends as thermal exposure time increased; there was no obvious fluctuation in the 2Ta alloy after thermal exposure from 0 to 4000 h, but it significantly decreased after thermal exposure at 8000 h; the creep lives of the 5Ta and 8Ta alloys increased initially and then decreased, and the peak creep lives were 500 and 2000 h, respectively. With the addition of Ta, the steady-state creep rate continuously decreased, the creep life significantly increased, and the peak creep life shifted backward. Simultaneously, the degree and structural integrity of the rafted γ' precipitates after creep rupture increased steadily. Hence, the improvement of the creep life of the alloys was attributed to a combination of factors, such as the increase in the volume fraction of the γ' precipitates in the initial state of the creep, the increase in rafted structural integrity, and thickness of the rafted γ' precipitates during the creep process.

近年来，随着航空航天发动机的持续发展，对其关键热端部件的承温能力要求越来越高，而高温合金共格组织热稳定性是影响其力学性能的关键因素，本工作在团簇成分式[Al-Ni₁₂](Al₁(Ti, Nb, Ta)_0.5(Cr, Mo, W)_1.5)基础上，保持其他元素含量不变，改变Cr、Mo、W的含量设计了系列镍基高温合金(含Cr_1.0Mo_0.5的S1-CM、Cr_1.0W_0.5的S2-CW和含Cr_0.7Mo_0.4W_0.4的S3-CMW)，研究Cr、Mo、W含量变化对合金γ /γ′共格组织热稳定性的影响。采用非自耗真空电弧炉制备合金铸锭，并对其在1300℃固溶15 h后在900℃下进行长期时效处理，并对时效态样品进行微观组织表征和力学性能测试。结果表明，这3个合金的微观组织均表现为高体积分数(f > 70%)的γ′粒子均匀地分布在fcc-γ基体中。其中，S1-CM和S2-CW合金在900℃、50 h时效后γ′粒子形貌均呈椭球形，而S3-CMW合金则表现为方形，这是由于后者具有更负的γ /γ′点阵错配度(后者δ = -0.47%，前者δ = -0.25%~-0.33%)。500 h长期时效后，各合金中的γ′粒子形貌没有发生变化，且都具有较慢的粗化速率(K = 10~18 nm³/s)；尤其S3-CMW合金表现出最高的γ /γ′共格组织稳定性(γ′粒子的粗化速率K = 10.02 nm³/s)，且晶界处的第二相粒子析出明显低于其他合金。系列合金的硬度基本不随时效时间发生变化，也进一步表明了共格组织的稳定性；其中S3-CMW合金的显微硬度为397~418 HV，时效200 h后的室温压缩屈服强度为818 MPa。

The nickel base powder superalloy prepared by modern powder metallurgy (PM) technology is selected because it has the characteristics of compatibility with strength and damage tolerance. Moreover, it is the preferred material for the fabrication of a new generation of aero-engine turbine disks. In this study, experimental techniques, such as FESEM and TEM, are used to systematically evaluate the creep properties of powder metallurgy nickel base superalloys with different Ta contents under the conditions of 750°C and 600 MPa. Additionally, the characteristics of microstructure and defosrmation behavior during creep and the effect of stacking fault energy of the alloy on creep property are also investigated. The results show that with increase in Ta content, the energy associated with alloy stacking fault decreases, demonstrating a nonlinear relationship. The deformation behavior and dislocation configuration changes in each creep deformation stage are closely related to the stacking fault energy. The stacking fault energy of alloys with low Ta content is relatively high, the matrix dislocation a/2<110> is prevented at the γ/γ' interface, and the dislocation is not easy to decompose. Furthermore, it can directly enter the γ' phase to form antiphase boundary or to bypass the γ' phase through the Orowan ring bow bending mode. If the alloy contains a moderate amount of Ta, the stacking fault energy of the alloy is reduced, promoting the decomposition of matrix dislocations at the γ/γ' interface. This results in a/6<112> Shockley incomplete dislocations and starts to shear the γ' phase, forming superlattice stacking faults (superlattice intrinsic stacking faults (SISFs) or superlattice extrinsic stacking faults (SESFs)) and extended stacking faults (ESFs), which are then transformed into deformation twins. Therefore, presenting the co-strengthening effect of stacking faults and deformation twins, which improves the creep property. The stacking fault energy of alloys with high Ta content is very low, which is favorable to the simultaneous formation of wide-sized ESFs on different {111} slip planes. The occurrence of inter-crossing stacking faults inhibits the formation of deformation twins and accelerates the development of creep deformation cracks. These experimental results demonstrate that the addition of an appropriate amount of Ta to the alloy can effectively reduce the stacking fault energy, improve the ability to form both partial dislocation shear γ' phase and micro-twins, increase creep resistance, and effectively improve the alloy creep property.

采用FESEM、TEM等实验技术，系统研究了750℃、600 MPa条件下，不同Ta含量的镍基粉末高温合金的蠕变性能和蠕变过程中显微组织和变形行为特征以及合金层错能对蠕变行为的影响。结果表明，随着Ta含量的增加，合金层错能呈非线性关系降低。蠕变变形各阶段的变形行为和位错组态的变化与层错能密切相关。低Ta含量合金层错能相对较高，基体位错a/2&lt;110&gt;滑移被阻止在γ/γ'内界面处，不易发生位错分解，可直接进入γ'相中形成反相畴界(APB)或通过Orowan环弓弯模式绕过γ'相；当合金中Ta含量中等时，合金层错能降低，促进在γ/γ'内界面处基体位错发生分解，产生a/6&lt;112&gt; Shockley不全位错开始剪切γ'相，形成超点阵层错(超点阵内禀层错(SISF)或超点阵外禀层错(SESF))和扩展层错(ESF)进而转化形成形变孪晶，呈现层错和形变孪晶共同强化效应，提高蠕变性能；而高Ta含量合金层错能很低，有利于位错在不同{111}滑移面上同时形成尺寸较宽的扩展层错，并出现相互交结的交叉层错抑制形变孪晶的形成，加快蠕变形变裂纹发展。因此，合金中加入适量Ta能有效降低层错能，提高形成不全位错剪切γ'相能力和形成显微孪晶能力，增加蠕变抗力，有效改善合金蠕变性能。

GH4169 superalloys are used in gas turbine engines and power plants owing to their excellent mechanical properties and corrosion resistance at temperatures exceeding 600oC. Because of their service condition, involving high temperature and complex stress, much attention has been attracted to the effect of temperature and loading mode on the mechanical properties and deformation mechanism. The effect of the loading mode, especially the multiaxial or coupled loading, on the mechanism of plastic deformation is still an outstanding open question despite numerous investigations on the effect of temperature on mechanical properties. In this study, the effect of tension-torsion coupled loading on deformation behavior was investigated, where the microstructures and underlying mechanism were revealed using SEM, TEM, EBSD, and neutron diffraction. It is found that the mechanical properties are dependent on the tension-torsion loading. For the tension specimens, the yield and ultimate strengths increase with the pretorsion angle; for instance, at the pretorsion angle of 720°, the increase rate is approximately 150% and 13%, respectively. At the pretension strain of 20%, the yield strength and elongation increase by approximately 31% and 16%, respectively. The density of dislocations increases in those samples after tensile and torsional deformations compared to the undeformed samples. Moreover, the density of dislocations for specimens deformed under the coupled loading is lower than those deformed under axial loading, indicating the dislocation annihilation effect. The yield strength is enhanced due to the strengthening effect of the initial dislocations produced during the preloading. The ultimate strength for the torsional specimens after pretension decreases because of the dislocation annihilation effect during the subsequent coupled loading. However, for the tensile specimens after pretorsion, such dislocation annihilation effect can be counteracted to some extent by the strengthening effect of the formed gradient structure by pretorsion on mechanical strength. These findings provide some insight into the regulation of the microdeformation mechanism process of materials through designing the coupled or multiaxial loading modes and the coordinated improvement of strength and toughness based on the achievement of gradient or hierarchical microstructure.

研究镍基高温合金在近服役条件下的力学性能与内在变形机理具有重要意义，但现有研究主要集中于单轴加载下的力学行为，多轴加载相关研究报道较少。为此，本工作对比研究了单轴和复合加载下多晶镍基高温合金GH4169的力学性能变化规律及其微观变形机制差异。在25℃下对多晶镍基高温合金GH4169进行拉伸-扭转复合加载，结合SEM、TEM、EBSD和中子衍射研究了加载方式对其力学性能、微观组织以及变形机理的影响。结果表明，拉伸样品的屈服强度和极限强度均随预扭转角度增加而增大(增幅分别约为150%和13%)；在20%预拉应变下，扭转样品的屈服强度和延伸率均有所增加(增幅分别约为31%和16%)。拉伸和扭转变形后样品中的位错密度明显增大；同时复合加载下位错密度相较于单轴加载略小，表明存在位错湮灭效应。预加载产生的位错强化效应提高了屈服强度，而随后复合加载下位错湮灭效应使预拉伸扭转样品的极限强度有所降低。预扭转形成梯度结构的力学强化作用一定程度上抵消了位错湮灭效应的影响。研究表明，多轴加载方式可调控材料微观结构和变形机制，进而实现材料强度和韧性的协调提升。

Nickel-based powder metallurgy superalloys have the characteristics of uniform structure, fine grains and no macrosegregation. Due to their excellent mechanical properties, such as excellent fatigue resistance, creep resistance, excellent high-temperature strength and crack propagation resistance, they have become the preferred materials for critical hot-end components such as aero engine turbine disks. Selective laser melting (SLM) has a high ability to form complex shape of parts, reducing post-machining procedures and completing efficient productions with low component volumes, so it has become a new technical route for the preparation of superalloys. In this work, the FGH4096M alloy was prepared by SLM technique with pre-powders prepared by vacuum induction argon atomization method. The microstructure and mechanical properties of the as build and heat-treated (HTed) alloys were investigated by OM, SEM, EBSD and so on. The as build alloy with a small number of γ' and carbide, mainly composed of austenite matrix γ phase, has the highest elongation. After heat treatment, a large amount of γ' phase precipitated in the alloy, which is one of the main factors affecting the mechanical properties of the alloy. The uniform and dense distribution of γ' precipitates in the alloy can significantly improve the strength. A higher lattice distortion between the γ' phase with cubic or petaloid shape and matrix can increase the strength of the alloy to some extent. Fine dendritic and equiaxed structures in SLM FGH4096M can improve the property of the alloy as fine grain strengthening. The higher solution temperature promotes the recovery and recrystallization of the SLM alloy, and eliminates the intra-crystal dendritics and equiaxed structures. The average elongation of the as build alloy is 24.97%. The yield strength and ultimate strength of the SLM FGH4096M alloy after direct ageing treatment are the highest, and the average values are 1459.46 and 1595.56 MPa, respectively.

以Ar气雾化法制备镍基高温合金粉末，利用选区激光熔化(SLM)技术制备了FGH4096M合金。运用OM、SEM、EBSD等手段研究了SLM沉积态和热处理态合金的组织和性能。结果表明，沉积态合金以奥氏体γ相基体为主，具有最高的延伸率。热处理后合金内析出大量的γ'相，γ'相均匀致密分布于合金内，能够明显提高合金强度。立方状或花瓣状γ'相与基体存在较高的晶格畸变，也能增加合金强度。精细的树枝结构和等轴结构对合金起到细晶强化作用。较高的固溶温度会促进SLM合金内回复和再结晶的发生，同时消除晶内树枝结构和等轴结构。沉积态合金平均延伸率为24.97%。经直接时效处理后的合金屈服强度和极限强度最高，其平均值分别为1459.46和1595.56 MPa。

Here some critical issues existed during forging process of Inconel 718 disks involving recrystallization mechanisms, grain growth, δ-phase morphology control and residual stress are explained. Based on the potential application prospect of selective laser melting in additive manufacture of aerocraft engine components, the specialized anisotropic microstructure and mechanical performance resulted from the rapid solidification process in selective laser melting are analyzed. Furthermore, the importance and difficulty of heat treatment in eliminating Laves-phase as well as tailoring substructure and related mechanical behavior are also discussed. The deformation mechanisms of Inconel 718 alloy at high temperature are illustrated in detail, comprising of dislocation planar slip, twinning and dislocation-shearing γ″ precipitates in complex modes. At last, a newly developed wrought nickel superalloy (Allvac 718Plus, with a increase in service temperature of 55 ℃ as compared to that of Inconel 718) is introduced, and some recent progresses aimed at modifying chemical compositions and phase compositions to improve service temperature on the basis of Inconel 718 alloy are also reviewed. The results indicate that the more stable γ″-γ' composite structure is important for the further design of next-generation wrought nickel superalloys.

本文首先针对Inconel 718合金的锻造工艺过程,较为系统地阐述了合金高温变形时的再结晶机制、晶粒长大、δ相形态控制以及存在的残余应力问题。基于选区激光熔化技术在航空发动机材料增材制造领域的潜在优势和应用前景,分析了选区激光熔化技术制造Inconel 718合金凝固组织和性能的各向异性,探讨了热处理工艺在消除有害相、改变组织结构及力学行为等方面的重要作用和局限性。结合高温服役过程的组织演变,分析了Inconel 718合金变形时涉及位错滑移、孪生、γ″相剪切方式的变形机制。最后,介绍了通过调整Inconel 718合金成分来改变强化相结构,从而进一步提高变形高温合金服役温度的有效尝试(如Allvac 718Plus合金的服役温度提高了55 ℃),指出了通过成分调整来获得热稳定性优异的γ″-γ'复合析出结构是新型变形镍基高温合金的重要发展方向。

Inconel 718高温合金广泛应用于航空、航天、电力和国防等领域中复杂金属结构构件的制造, 其高温抗疲劳性能和蠕变持久强度与成形加工过程中微观组织的演变密切相关. 以往的研究侧重于镍基合金热加工(如定向凝固、热处理、锻造和焊接等)工艺参数的优化, 较少从析出相控制的角度来阐明冷轧、热变形、焊接等工艺与高温服役性能之间的内在联系. 本文介绍了该合金中不同类型的析出相, 包括: 主要强化相(&gamma;'' 相)、辅助强化相(&gamma;' 相)、&gamma;'' 相的平衡相(&delta;相), 以及MX型碳氮化物和Laves相; 论述了镍基合金制备过程中不同类型析出相的析出机制及其对合金高温性能的影响; 指出了镍基合金高能电子束焊接过程中, 焊接热影响区微裂纹形成的影响因素.

High temperature tensile creep behaviors of cast nickel—based superalloy K44 in the temperature range of 850---900℃ and under the applied stress range of 225---380 MPa have been studied. The results indicate that all of the creep curves of test alloys have similar shape: a short primary creep and a dominant accelerated creep stage, and the long accelerated stage is due to the interaction between rafting r’ particles and dislocations. As the creep strain is a softening stage, the accelerated creep can be approximately described by expression. The creep fracture data follow the Monkman--Grant relationship. Cracks originate from the cavities at grain boundary or interdendritic.

研究了铸造镍基高温合金K44在850---900℃, 225---380 MPa的高温拉伸蠕变行为.结果表明, 实验合金蠕变曲线具有较短的初始阶段和较长的加速阶段, 加速阶段较长是由于筏形化的r’粒子和位错相互作用促成的. 加速蠕变为应变软化阶段时, 可以由关系式来描述. 蠕变断裂数据遵守Monkman--Grant规律, 裂纹起源于晶界或枝晶界的空洞.

通过改变固溶热处理温度、保温时间和固溶后冷却方式, 研究了不同固溶热处理工艺对一种新型铸造高温合金组织和性能的影响. 结果表明, 将合金在不同温度固溶处理2 h后空冷, 合金在760 ℃, 660 MPa和 980 ℃, 180 MPa条件下的持久寿命随热处理温度的升高先升高而后降低; 固溶处理温度为 1220 ℃时, 760 ℃, 660 MPa条件下的持久寿命达到最高; 固溶处理温度为1180 ℃时, 980 ℃, 180 MPa条件下的持久寿命最高; 当热处理温度从1120 ℃升高到1220 ℃时, 拉伸强度随温度升高而增加, 继续升温到1240 ℃, 拉伸强度下降. 当固溶热处理温度为1120℃, 处理时间在2---8 h范围内变化时, 合金在760 ℃, 660 MPa条件下的持久寿命随时间延长而降低, 而在980 ℃, 180 MPa条件下的持久寿命随处理时间延长而升高; 当热处理时间为2和4 h时, 拉伸强度较高; 延长到6和8 h时, 拉伸强度下降. 当冷却方式不同时, 合金持久性能也发生变化. &gamma;'相和&gamma;/&gamma;'共晶组织在尺寸、形态、分布和数量上的变化是导致合金力学性能变化的关键因素.

The microstructure evolution and its effect on the impact toughness of a new Ni-Fe based alloy GH984G, used in 700 °C ultra-super critical coal-fired power plant, were investigated during thermal exposure at 650 °C-750 °C for up to 10,000 h. The results show that the impact toughness at room temperature drops rapidly at the early stage during thermal exposure at 700 °C and then has no significant change even if after exposure for 10,000 h. The significant decline of the impact toughness is attributed to the coarsening of M23C6 carbides at grain boundaries, which weakens the grain boundary strength and leads to the aging-induced grain boundary embrittlement. The M23C6 carbides have almost no change with further thermal exposure and the impact toughness also remains stable. Additionally, the impact toughness rises with the increase of thermal exposure temperature. The size of γ′ after thermal exposure at 750 °C for 10,000 h is much bigger than that at 650 °C and 700 °C for 10,000 h. Therefore, the intragranular strength decreases significantly due to the transformation of the interaction between γ′ and dislocation from strongly coupled dislocation shearing to Orowan bowing. More plastic deformation occurs within grains after thermal exposure at 750 °C for 10,000 h, which increases the impact toughness.