Abstract Stray grains bring great challenges to the production of superalloy single-crystal blades using the Bridgman method. The height difference between the liquidus isotherms in the airfoil and platform, which is induced by the difference between liquidus isotherm advancing velocity and withdrawal rate, provides undercooling for the nucleation and the growth of stray grains. The height range of liquidus isotherm is used for the first time to describe the asymmetric distribution of temperature and radiation, and to estimate the probability of stray grain formation. A real-time adjustment of withdrawal rate method is proposed to design the withdrawal rate-time curve aiming to fabricate superalloy single-crystal blades with complex geometry. The obtained withdrawal rate curve is then validated by numerical simulation and hence applied to the fabrication of single-crystal blades. The simulation results show that with obtained withdrawal rate curve the distribution of radiation and temperature are significantly improved and the undercooling in the platform is largely reduced. The observed macrostructure in the experiments proves that the stray grains in the platform can be avoided through the designed withdrawal rate curve. The proposed method for designing withdrawal rate can provide a reliable strategy for the research and manufacture of stray-grain-free single-crystal blades.

中文翻译：

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高温合金单晶叶片制造变拔速设计

摘要 杂散晶粒给使用布里奇曼法生产高温合金单晶叶片带来了巨大挑战。由液相线前进速度和撤回速度之间的差异引起的翼型和平台液相线等温线之间的高度差为杂散晶粒的成核和生长提供了过冷。首次使用液相线等温线的高度范围来描述温度和辐射的不对称分布，并估计杂散颗粒形成的概率。针对复杂几何形状高温合金单晶叶片的制备，提出了一种实时调整拉拔速率的方法来设计拉拔速率-时间曲线。然后通过数值模拟验证获得的提取率曲线，从而应用于单晶叶片的制造。仿真结果表明，得到的提取率曲线显着改善了辐射分布和温度分布，大大降低了平台过冷。实验中观察到的宏观结构证明，通过设计的提取率曲线可以避免平台中的杂散颗粒。所提出的提取率设计方法可为无杂散单晶叶片的研究和制造提供可靠的策略。仿真结果表明，得到的提取率曲线显着改善了辐射分布和温度分布，大大降低了平台过冷度。实验中观察到的宏观结构证明，通过设计的提取率曲线可以避免平台中的杂散颗粒。所提出的提取率设计方法可为无杂散单晶叶片的研究和制造提供可靠的策略。仿真结果表明，得到的提取率曲线显着改善了辐射分布和温度分布，大大降低了平台过冷。实验中观察到的宏观结构证明，通过设计的提取率曲线可以避免平台中的杂散颗粒。所提出的提取率设计方法可为无杂散单晶叶片的研究和制造提供可靠的策略。