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

Abstract

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.

Keywords

• nickel-based superalloy
• turbine guide vanes
• single crystal growth
• grain continuator technology
• crystallographic orientation
• stray grain defect