The effects of temperature, strain rate and plastic strain on flowbehavior and microstructures of GH4586 wrought superalloy wereinvestigated by compressive deformation performed on MTS machine atdeformation temperatures of 950 to 1150℃ and strain ratesof 0.001 to 1 s-1. The results show that the flow stress increasesdrastically with the decrease of deformation temperature and the increaseof strain rate. Dynamic recrystallization process can be effectivelypromoted by increasing deformation temperature. When deformationtemperature is higher than 1100℃, completely recrystallizedmicrostructures can be obtained with engineering strain of 30%, whilewhen the temperature is lower than 1050℃, dynamic recrystallizationdoes not occur with engineering strain up to 40\%. Grain size of annealedmicrostructures increases with the increase of deformation temperature.Ideal plasticity and resultant microstructures can be achieved by effectivecontrol of deformation temperature.

在MTS热模拟实验机上采用热压缩实验的方法研究了在温度为950—1150℃、应变速率为0.001—1 s-1的实验条件范围内，GH4586合金高温塑性变形过程中变形温度、应变速率及变形量等工艺参数对流变应力和微观组织的影响。结果表明, 流变应力随着变形温度的降低和应变速率的提高而迅速增大。提高变形温度能够有效的促进动态再结晶过程, 在1100℃以上变形时, 在30%的工程应变量下即能够获得完全再结晶的锻态组织；当变形温度低于1050℃时, 工程应变超过60%仍未观察到动态再结晶。在变形量与热处理制度一定的条件下, 材料热处理后的晶粒度随变形温度的升高而增大。有效控制材料的变形温度是获得良好热加工塑性、降低变形抗力和获得均匀微观组织的关键措施。

etc. These products are widely used in aviation, aerospace, energy, petrochemical, nuclear power and other industrial fields. In this paper, domestic progress of wrought superalloys in recent ten years was reviewed, including advances in fabrication process, research in new alloys (GH4169G, GH4169D, GH4065 and GH4068 alloy et al.) and new techniques (deforming of FGH4096 alloy, nitriding of NGH5011 alloy and 3D printing of In718 alloy et al.).]]>

变形高温合金是指通过铸造-变形工艺生产的高温合金,包括盘、板、棒、丝、带、管等产品,该类产品广泛用于航空、航天、能源、石化、核电等工业领域。本文介绍了国内变形高温合金近10年的最新进展,分别从变形高温合金的制备工艺流程,GH4169G、GH4169D、GH4065、GH4068等新合金的研制,以及FGH4096的变形化、NGH5011的氮化、In718合金的3D打印等新技术3个方面展开论述。

et al. These alloys can provide a promising solution of high reliability combined with low life cycle cost for military and commercial gas turbines. Nonetheless, in order to maximize the advantageous of cast-wrought disc alloys on reliability and cost-effective ratio, the comprehensive understanding about the prevention and identification of metallurgical defects, increase in the yield rate of materials during conversion, processing of fine-grained billets and dual-property disc forgings, is still needed.]]>

近年来一系列新型的高性能变形高温合金盘材在航空发动机和燃气轮机上获得了重要应用,这些盘材合金在追求高承温能力的同时更加注重服役性能、工艺性能与全寿命成本之间的平衡。国内在三联熔铸直径508 mm自耗锭、多重循环热机械处理制备直径300 mm以上细晶棒材、盘件热模锻成型与组织性能控制等关键制备技术取得突破的基础上,成功研制了GH4065、GH4720、GH4175与GH4975等一系列高性能盘材合金及全尺寸锻件,为先进军用涡扇发动机、大涵道比商用发动机提供了高可靠性、低成本的盘件选材方案。为充分发扬变形盘材在可靠性与成本方面的特有优势,需要在高性能盘材的合金设计与成分优化、自耗锭冶金缺陷的预防与识别、自由锻开坯的效率与成材率提升、双组织双性能盘件制备等方面进一步开展深入的研究工作。

In order to control the grain size of forged turbine disk of wrought superalloy like GH4738 more effectively, constitutive equations and grain structure evolution models of GH4738 alloy are used in Deform 3D (TM) for achieving integrated simulation of whole forging process of GH4738 alloy turbine disk (from preheating billet for upsetting to die forging). By using of integrated simulation, the variation of temperature, average grain size, etc., during the whole forging process has been explored, making it possible to control these parameters quantitatively. Comparing with traditional simple stage simulation, results of integrated simulation are more consistent with corresponding experimental results of forged turbine disk (300 mm in diameter). Therefore, the reliability of the integrated simulation is verified. Finally, with the application of integrated simulation, GH4738 alloy turbine disk with a diameter of 1450 mm has been successfully forged by 8x10(4)t forging press. This work provides a more practical simulation method for helping the process design of forging large turbine disk.

TM软件对该合金涡轮盘从自由锻前预热直至模锻完成的整个锻造过程的集成式模拟. 借助集成式模拟实现了对锻件在整个锻造过程中温度、平均晶粒尺寸等参数的定量控制. 同时采用直径300 mm涡轮盘的实际锻造结果验证了所用模型和该模拟方法的可靠性. 最后, 把集成式模拟运用于直径1450 mm涡轮盘盘件的锻造过程模拟, 并根据模拟优化方案在8×104 t锻压机下成功锻制直径1450 mm涡轮盘盘件. 为大型变形高温合金涡轮盘的锻造成型提供了工艺优化的理论依据和研究方法.]]>

η-phases, block M3B2 borides and MC carbides are formed in the forged condition. It is confirmed by the thermodynamic calculations that the η-phases, M3B2 borides and MC carbides are much easier forming in the freckle than that in matrix. After heat treatment, compared with matrix, the lathy η-phases are still existed in the freckle; the size and quantity of primary γ′ phases increase significantly while the size and morphology of the secondary γ′ phase are basically identical, only with less quantity. It has been found that due to the high content of γ′ phase, the γ′ dissolution temperature in the freckle is higher than that in the matrix. This induces an impeded recrystallization process caused by the coarsened γ′ phases during forging process and the grain size of the freckle region is significantly smaller than that of matrix. Based on this study, the formation of freckle can be effectively controlled by meticulous controlling of the previous smelting process, releasing of electrode residual stress, suitably reducing VAR melting rate, and accelerating VAR cooling.]]>

η相、块状M3B2型硼化物与MC型碳化物。热力学相计算亦证实了点状偏析区较正常组织区域更容易生成η相、M3B2和MC。热处理后,与正常组织区域相比,点状偏析中仍存在板条状η相,一次γ′相的尺寸和数量明显增加,二次γ′相尺寸和形貌基本相同但数量减少。分析发现,由于点状偏析区的成分变化使得γ′相回溶温度升高,导致锻造中粗大γ′相阻碍再结晶长大,点状偏析区晶粒尺寸小于正常组织区域。采取前道次冶炼精细化控制、释放电极残余应力、适度降低真空自耗重熔熔化速率、加强真空自耗重熔冷却等措施,可以有效降低点状偏析的形成倾向。]]>

利用热力学计算软件Thermo-Calc与相应的Ni基高温合金数据库,从热力学角度通过计算最小吉布斯自由能,得到GH586合金可能析出的平衡相,并预测化学成分对析出相的影响,分析各相的析出规律,为挖掘合金组织潜力和改善合金使用性能提供理论依据.

The elimination of the segregation improves the thermo plasticity of superalloy ingot during the homogenization process, but coarser grain structure and high-temperature oxidation caused in further homogenization have an adverse impact on the thermo plasticity. The inheritance of coarse grain structure in the followed hot working process increases the tendency of cogging crack and makes the grain refining harder, leading to a lower yield of the final workpiece. The microstructure characteristics and their hot deformation behaviors of GH4740H, GH4738, GH3625 and 690 alloys under different homogenizations were investigated by means of microstructure analysis methods and crack propagation testing. The experimental results show that the reasonable homogenization processing needs to take into account the segregation elimination arising thermo plasticity addition, more to consider grain coarsing and severe oxidation leading to decrease plasticity. Based on the residue dendrites can provide more recrystalazation nucleation sites, the partial homogenization possessing probably exists rationality. This research work provides an exploratory study for the improvement of the homogenization-cogging process of superalloy.

利用OM, SEM和裂纹扩展速率测试等手段分析了GH4740H, GH4738, GH3625和690合金不同均匀化程度下的组织特征以及这些组织状态的热变形行为, 系统研究了合金均匀化工艺因素与再结晶的关联规律. 研究结果表明, 合金均匀化需要兼顾枝晶偏析消除带来的热塑性改善以及晶粒长大和氧化加剧所导致的后续热变形时的塑性下降; 合金未完全均匀化留下的残留枝晶间区域提供了再结晶形核位置, 提高再结晶形核率. 在相同热变形条件下, 有残留枝晶组织的试样再结晶程度明显高于完全均匀化、无枝晶组织的试样. 为此提出基于部分均匀化制度的高温合金均匀化开坯控制方法具有合理性.

Much attention has been paid to the development of more advanced materials for high-pressure compressor and turbine discs of gas turbine engines. A high performance wrought superalloy GH4065 for disc applications has been recently developed based on the comprehensive evaluation of a series of model alloys with characteristic chemical composition, lattice parameter, particularly γ’ volume fraction. The concentration of major alloying elements of GH4065 is closely similar with René 88 DT and specifically optimized considering the demands of ingot metallurgy technologies. Therefore, GH4065 can be considered as an ingot metallurgy version of powder metallurgy René 88 DT. Large scale vacuum arc remelting (VAR) ingots of GH4065 alloy with diameter up to 508 mm have been produced via standard triple melting techniques. Micro-scale segregation of alloying elements on large VAR ingot has been effectively suppressed due both to optimized alloying elements concentration and to improved melting techniques. Ultra-low carbon content (less than 0.02% in mass fraction) significantly decreases the dendritic segregation tendency of certain alloying elements and promotes the uniformity of microstructures. VAR ingot of GH4065 exhibits extraordinary hot plasticity, ingot conversion can be accomplished using conventional open die forging procedure. Fine and uniform γ+γ’ duplex structures can be obtained on billets and disc forgings via a newly developed multi-cycle thermomechanical processing method. The flow stress data show that the formation of γ+γ’ microduplex results in a significant decrease of flow stress in comparison with γ’ dispersion structures under exactly the same deformation conditions. The distribution of strain rate sensitivity m in relationship with temperature and strain rate accurately identifies a specific domain within which γ+γ’ microduplex exhibits superplasticity. Full-scale turbine discs of GH4065 alloy with diameter of 630 mm achieve an optimal combination of creep resistance, fatigue lifetime and ductility. GH4065 discs exhibit extraordinary microstructural and property stability during prolonged thermal exposure, which means that dendritic segregation has been successfully restricted to an acceptable level. The results reveal that highly alloyed disc alloys produced via ingot metallurgy techniques exhibit lower costs and higher productivity, and can still meet the ever increasing demand of high performance gas turbine engines.

在对一系列高合金化模型合金进行系统比选研究的基础上, 发展了新型的GH4065变形高温合金, 该合金化学成分与René 88 DT合金类似, 并针对铸锻制备工艺的要求进一步实施了优化. 研制结果表明, 应用三联低偏析熔铸和多重循环热机械处理等新型技术生产的GH4065合金, 适用于制备先进航空发动机关键热端转动部件, 综合性能完全满足高压压气机盘和低压涡轮盘的工况要求, 必要时可以作为高压涡轮盘的高可靠性、低成本解决方案. 随着变形高温合金材料和制备工艺的发展, 应用铸锻工艺制备的高性能涡轮盘材料能够满足先进航空发动机的技术要求.