利用引晶技术制备大尺寸镍基单晶涡轮导向叶片

Manufacturing of large size nickel-based single crystal turbine guide vanes by grain continuator technology

采用引晶技术制备了大尺寸双联镍基单晶涡轮导向叶片。利用高速凝固法(high rate solidification,HRS)进行单晶叶片定向凝固,并对单晶叶片进行宏观腐蚀,揭示叶片单晶完整性。通过扫描电镜、电子背散射衍射(EBSD)技术及高温持久实验,评估单晶叶片实际性能。同时,利用有限元模拟软件ProCAST对单晶叶片的定向凝固过程进行数值模拟及分析。结果表明:采用引晶技术可有效避免杂晶缺陷的形成,并可成功制备单晶完整性良好的大尺寸双联涡轮导向叶片,但在Vane 1叶片主晶与引入晶体之间仍会形成角度分别为1.5°和2.7°小角度晶界(LABs)缺陷;LABs使得单晶叶片的高温持久性能虽稍有降低(寿命损失小于15%、断后伸长率损失小于7%),但仍可满足叶片的服役性能。根据ProCAST软件对大尺寸双联单晶导向叶片凝固过程的模拟结果得知,设置引晶结构后,叶片的原始凝固路径得到了优化,叶片前缘位置的过冷条件得到了改善,杂晶缺陷的形核概率得到了降低,有效避免了杂晶缺陷的形成。

Large size nickel-based single crystal twin turbine guide vanes(TGVs)were prepared by grain continuator(GC)technology.Directional solidification was performed in a high-rate-solidification(HRS)Bridgman vacuum furnace.Then,the macro-etching test was carried out to reveal the single crystal integrality of TGVs.Scanning electron microscopy(SEM),electron backscatter diffraction(EBSD)technology,and high temperature stress rupture experiment were applied to evaluate the actual properties of TGVs.Simultaneously,the professional finite element modeling(FEM)ProCAST software was used to simulate the directional solidification process of single crystal TGVs.The experimental results show that the formation of stray grain(SG)defect can be avoided effectively,and integrity large size single crystal twin TGVs can be prepared successfully by adopting GC technology.However,the low angle grain boundaries(LABs)defects are formed inevitably,and the boundaries angle between primary crystal and GC crystal in Vane 1 are 1.5°and 2.7°respectively.Despite the mechanical performance at high temperature degrades slightly(stress rupture life loss less than 15%,and elongation loss less than 7%),the service performance of TGVs is still satisfied perfectly.According to the solidification process results of the large size twin TGVs simulated by ProCAST software,it is found that the initial solidification path of TGVs is optimized,meanwhile,and the undercooling condition at the leading edge of TGVs is improved by adding the GC structure.In addition,the nucleation probability of SG defect is reduced significantly,and the formation of SG defects is avoided effectively.