重型燃机用大尺寸UGTC47定向柱晶叶片中雀斑的形成机理及其对持久性能的影响

Formation Mechanism of Freckles in Large-Sized UGTC47 Directionally-Solidified Columnar Crystal Blades for Heavy-Duty Gas Turbines and Influence on Stress Rupture Property

摘要:

采用光学显微镜、扫描电子显微镜、持久试验等手段对重型燃气轮机用大尺寸UGTC47定向柱晶叶片中雀斑的形成机理及其对持久性能的影响进行了研究。结果表明，在叶片榫头的中部和根部区域出现雀斑缺陷，形成机制为偏析导致的液相密度反转，在重力的作用下引起熔液对流，导致了枝晶臂断裂从而形成雀斑。在900 ℃/380 MPa时，雀斑面积分数对UGTC47合金的持久性能产生明显影响。随着雀斑含量的增加，合金的持久寿命由无雀斑时的131.83 h下降到雀斑含量62%时的33.66 h。

Abstract:

The formation mechanism of freckle defects in large-sized UGTC47 directionally-solidified columnar crystal blades for heavy-duty gas turbines and their effect on the stress rupture property were investigated using optical microscope, scanning electron microscope, and endurance performance test. The results indicate that freckle defects form in both the middle and root regions of the blade tenon, whose formation mechanism is the density inversion caused by liquid phase segregation, resulting in fluid convection under the action of gravity, and leading to the fracture of dendrite arms and the formation of freckles. At 900 ℃/380 MPa, the proportion of freckle area has a significant impact on the endurance performance of the UGTC47 alloy. With the increase in freckle content, the stress rupture life of the alloy is decreased from 131.83 h without freckle defects to 33.66 h with freckle content of 62%.