一种第三代单晶高温合金铸件表面层组织研究

Investigation on the Surface Layer of Blade Castings of a Third Generation Single Crystal Superalloy

摘要:

采用一种第三代单晶高温合金制备了某型号的涡轮叶片铸件，经真空固溶热处理后，发现在叶片铸件表面形成了大量形状不规则的亮白色组织。经对叶片进行解剖和金相观察，发现铸件内部组织为均匀的γ相，但外部存在一个明显的表面层。表面层中基体为连续分布的亮白色γ’相，主要组成元素为Ni，Al和Ta，表面层γ’相基体上析出了许多片状的TCP相。对铸件表面附近的成分分布进行了测量分析，显示铸件表面层为典型的贫Cr层。正是Cr元素的贫化，导致了表面层中γ相向γ’相的转变和γ’相与TCP相的共轭生长。贫Cr层的出现还导致了在表面层与内部组织之间出现了较多的残存γ/γ’共晶。

Abstract:

A batch of turbine blade castings were produced by using a third generation single crystal superalloy. After solution heat treatment, a large number of bright white spots with irregular shapes were observed on the blade surface. Through metallographic detection of the blade sections, a distinct surface layer was exhibited, in spite of the uniform γ phase structure in the internal area of the castings. The bright white substrate of the surface layer is determined to be continuous γ’ phase composed of Ni, Al and Ta elements. In the surface layer, a lot of lamellar TCP phases precipitated from the γ’ phase matrix. The element distribution near the surface of the casting was measured and analyzed. It was confirmed that the surface layer of the casting was a typical Cr-poor layer, leading to the phase transition from γ to γ’ and the coupled growth of γ’ and TCP phases. The depletion of Cr in the surface layer also resulted in the residual of γ/γ’ eutectic between the surface layer and the internal area.