随着航空发动机涡轮前温度的不断提升，研发新一代航空发动机涡轮叶片用单晶高温合金及其热防护涂层迫在眉睫。为了满足航空发动机复杂的服役环境对高温结构材料综合性能提出的严苛要求，在材料集成计算工程与材料信息学的推动下，近年来国内外逐步开展了单晶高温合金与热防护涂层的智能设计研究，以提高研发效率、降低研发成本。本文重点综述多尺度计算模拟与机器学习方法在推动新型单晶高温合金与热防护涂层设计上的最新研究进展，确证了多尺度计算模拟为揭示单晶高温合金强韧化机理与热防护涂层抗氧化、阻扩散机制所提供的有效理论支撑，展现机器学习在构建高温结构材料“成分-组织-性能”内禀关系上的可靠性与巨大潜力，为新一代高承温单晶高温合金与热防护涂层提供了智能高效的快速研发新路径。

以具有空心气冷结构涡轮叶片用第二代镍基单晶高温合金DD6为研究对象，研究试样厚度对其超高周疲劳性能的影响。基于有限元方法结合实测设计了工作段厚度为0.5 mm的超高频振动疲劳薄壁试样，实测一弯共振频率达到1425 Hz左右，采用电磁振动台开展超高周疲劳实验，获取最高至10⁹周次的疲劳S-N曲线，并开展与标准旋转弯曲疲劳、标准振动疲劳实验数据的对比分析。结果表明：DD6单晶高温合金的疲劳强度在10⁷~10⁹周次范围内下降约25%，薄壁试样高周疲劳强度和同材料标准旋弯疲劳强度基本一致，略低于标准振动疲劳强度；薄壁试样的裂纹在危险截面的表面萌生，呈线源特征，疲劳扩展区存在两个扩展平面，呈现类解理特征。

The effect of heating history, such as those related with standard heat treatment, hot isostatic pressing (HIP), coating and brazing thermal processes, on the microstructure and creep properties (at 760 oC/790 MPa and 980 oC/248 MPa) of a first generation nickel-based single crystal superalloy DD413 was investigated. The results show that the microstructure and creep behavior of nickel-based single crystal superalloy DD413 are significantly affected by different thermal processes. Compared with the standard heat treatment, HIP reduces the size of γʹ and γ channel, but increases the volume fraction of γʹ phase. Meanwhile, micro-pores in the alloy are effectively eliminated by HIP, which improves the creep life. The coating thermal process preparation can coarsen the γʹ and γ channel, reduce the volume fraction of γʹ phase, and delay the rafting kinetics of γʹ phase at high temperature, therewith, reduce the creep property of the alloy. The brazing thermal process not only causes the coarsening of γ′ phase but also destroys the cubic degree of γ′ phase, leading to significant reduction in creep property of the alloy.

对第一代单晶高温合金DD413进行标准热处理、热等静压、涂层热以及钎焊热工艺处理，然后在760 ℃/790 MPa和980 ℃/248 MPa条件下测试其蠕变性能，研究了不同热工艺对合金蠕变性能的影响。结果表明:不同的热工艺都显著影响DD413合金的微观组织和蠕变性能。热等静压后这种合金中的γʹ相和基体通道的尺寸减小，γʹ相的体积分数有所提高并且消除了合金中的显微孔洞，使合金的蠕变性能大幅度提高。涂层热工艺使合金中的γʹ相和基体通道粗化，γʹ相的体积分数和其在高温低应力下的形筏速度降低，不利于合金的中高温蠕变性能。钎焊热工艺不仅使合金中的γ′相粗化还破坏了γ′相立方度，因此合金的蠕变性能显著降低。

The microstructure and deformation mechanism of two "replacement of Re by W" type low-cost second-generation nickel based single crystal superalloys after fracture at 982℃/248 MPa and 1070℃/137 MPa were investigated by SEM and TEM. The results show that the stress rupture properties of two alloys both reached the level of the second-generation single crystal superalloys; After fracture γ′ phases connected and combined to form "N-type" rafted structure, and the degree of γ′ phases distortion increased with the distance from the fracture. Under the same conditions, the raft degree of γ′ phases in 8.5W+1.0Re alloy was lower than that in 8.0W+1.5Re alloy; At 1070℃/137 MPa, the interfacial dislocation networks of the two alloys became denser; However, the dislocation networks of 8.0W+1.5Re alloy were denser than that of 8.5W+1.0Re alloy, a<010> superdislocations shearing into the γ′ phases were observed after fracture in 8.5W+1.0Re alloy under both conditions; The unstable fracture of the two alloys was mainly ascribed to a/2<110> dislocations in γ matrix shearing into the rafted γ′ phases, which intensify the deformation of rafted γ′ phases, and results in initiation and propagation of microcracks at the γ/γ′ interface, eventually leading to the fracture of the alloy; The interfacial dislocation networks and a<010> superdislocations could both improve the creep resistance of the two alloys.

用扫描电镜(SEM)和透射电镜(TEM)观察两种“W替Re”型低成本第二代镍基单晶高温合金分别在982℃/248 MPa和1070℃/137 MPa条件下持久变形断裂后的微观组织，研究了其变形的机制。结果表明，两种合金的持久性能均达到第二代单晶高温合金的水平；持久变形断裂后γ'相连接并合并成“N型筏”结构，随着与距离断口位置的接近γ'相的扭曲变形程度加剧。在相同条件下8.5W+1.0Re合金γ'相的筏形化程度比8.0W+1.5Re合金低；与982℃/248 MPa条件相比，在1070℃/137 MPa下两种合金持久变形断裂后的界面位错网更加致密。在相同条件下，8.0W+1.5Re合金比8.5W+1.0Re合金的位错网更致密，8.5W+1.0Re合金在两条件下持久变形断裂后都能观察到剪切进γ'相的a<010>超位错；两种合金失稳断裂的主要原因是，γ基体中的a/2<110>位错剪切进入γ'相使筏形γ'相变形加剧，裂纹在γ/γ'界面处萌生和扩展，最终使合金断裂；γ/γ'两相界面上的位错网和a<010>超位错可在一定程度上提高合金的持久变形抗力。

The microstructural evolution during long-term aging at 1000℃ and 1130℃ and the stress rupture property at 1100℃/140 MPa of a fourth-generation nickel-based single crystal superalloy with 6Re/3Ru were investigated. The microstructure and dislocation configuration of the alloy were observed by field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM) in terms of its microstructural stability and stress rupture property. The results showed that the alloy displayed excellent microstructural stability. During long-term aging at 1000℃, γ′ phase grew up gradually, but γ′ phase still remained high cubic degree, however, the TCP phases did not precipitate after aging for 1000 h. After aging at 1130℃ for 500 h, the γ′ phase connected each other and became rafting ed. The TCP phase started to precipitate after long-term aging at 1130℃ for 200 h, however, the content of TCP phase was only 0.04% after aging for 1000 h in the alloy. After aging at 1130℃ for 500 h, dislocation networks formed at γ/γ′ interfaces which became more regular and denser with the increase of aging time. The stress rupture life of the alloy at 1100℃/140 MPa was 676.5 h, which reached the level of the fourth-generation nickel-based single crystal superalloy. The γ′ phase underwent N-type rafting, the needle-like TCP phase (μ phase) precipitated, and dislocation pile-up was found near TCP phase after fracture. During stress rupture test, the formation of γ/γ′ interfacial dislocation networks and a<010> super-dislocations in the alloy was beneficial to the stress rupture property.

用场发射扫描电镜(FE-SEM)和透射电镜(TEM)观察一种第四代镍基单晶高温合金长期时效和持久断裂后的微观组织和位错组态，研究了这种合金在1000℃和1130℃长期时效过程中的组织演化和在1100℃/140 MPa条件下的持久性能。结果表明：这种合金具有较好的组织稳定性，在1000℃长期时效过程中γ'相逐渐长大，但是在1000 h后仍有较好的立方度且没有TCP相析出。在1130℃长期时效500 h后γ'相发生连接和筏化；时效200 h后开始析出TCP相，时效1000 h后合金中TCP相的面积分数只有0.04%。在1130℃长期时效500 h后，γ/γ'界面形成位错网并随着时效时间的延长变得更加规则致密。这种合金在1100℃/140 MPa条件下的持久寿命为676.5 h，达到第四代镍基单晶高温合金水平。持久断裂后γ'相发生N型筏化，合金中析出针状TCP相(μ相)并在TCP相附近出现位错塞积。在持久试验过程中，合金中生成的γ/γ'界面位错网和a<010>超位错有利于提高其持久性能。

<p>Industrial gas turbines (IGTs) are the key equipment to achieving energy strategy, such as energy conservation and clean power generation. When the large and complex IGT blades are fabricated by the conventional Bridgman directional solidification process, the thermal gradients at the solidification front are low and unstable, resulting in some disadvantages: the coarse dendrite structure with severe dendritic segregation, the increased occurrence of casting defects and the poor performance of mechanical properties. These disadvantages provide a good opportunity for rapid development of the directional solidification with high thermal gradient (HG), such as the liquid metal cooling (LMC). In the present work, the physical basis of HG process, the microstructure, mechanical properties, solution heat treatment, and casting defects of the superalloys processed by HG process, have been reviewed. The HG process increases the thermal gradient and the cooling rate, thus permitting microstructural improvements including a more homogeneous fine-dendrite structure with lower elemental segregation and shrinkage porosity, and refinement of carbide, <i>γ′</i> phase and eutectic, reducing the volume fraction of eutectic and shrinkage porosity. During the solution heat treatment, the HG process increases the incipient melting temperature and reduces the residual segregation as well as the content of solution pore. The HG process could effectively inhibit the formation of freckle chains, increase the critical withdrawal rate of the stray grain formation, and decrease the degree of the misorientation of the <001> grain orientation from the casting axis. Moreover, the HG process could improve the mechanical properties including the stress rupture life, low-cycle fatigue (LCF), high-cycle fatigue properties and short-term strength, but the improvement might be reduced at higher temperature or under the oxidation condition.</p>

Microporosity in a single crystal nickel-based superalloy DD33 solidified by high rate solidification (HRS) and liquid metal cooling (LMC) process was investigated by the X-ray tomography (XRT). It is found that the pressure drop was reduced because of the larger volume fraction of eutectic in the alloy solidified by LMC, which results in less solidification-pore (S-pore) formation. Homogenization-pore (H-pore) forms in interdendritic regions during solution heat treatment, which results in the increase of volume fraction of porosities during heat treatment. However, lower level of H-pore in the LMC samples can be attributed to the finer dendrite arm spacing and the lower segregation.

采用高分辨透射X射线三维成像技术研究了传统高速凝固法(HRS)和液态金属冷却法(LMC)两种工艺制备的镍基单晶高温合金DD33中显微孔洞的三维尺寸信息, 结果表明: 与HRS相比, LMC工艺降低一次枝晶间距, 增加共晶体积分数, 使最后凝固阶段枝晶间的空隙尺寸变大, 压降降低, 最终降低了铸态孔的尺寸及体积分数。固溶处理后用两种工艺制备的合金中显微孔洞的体积分数都有所增加, 但是用LMC工艺制备的合金中较细的枝晶和较低的偏析程度, 使合金中固溶孔的体积分数显著低于用HRS工艺制备的合金。

An overview of the development and current status of the directional solidification process assisted by liquid metal cooling (LMC) has been presented in this paper. The driving force of the rapid development of the LMC process has been analyzed by considering the demands of (1) newer technologies that can provide higher thermal gradients for alleviated segregation in advanced alloy systems, and (2) better production yield of the large directionally solidified superalloy components. The brief history of the industrialization of the LMC process has been reviewed, followed by the discussion on the LMC parameters including selection of the cooling media, using of the dynamic baffle, and the influence of withdrawal rates and so on. The microstructure and mechanical properties of the traditional superalloys processed by LMC, as well as the new alloys particularly developed for LMC process were then described. Finally, future aspects concerning the LMC process have been summarized.