DD5镍基单晶高温合金凝固过程元素偏析的相场模拟

Phase Field Simulation of Alloying Element Segregation During Solidification of DD5 Nickel-Base Single Crystal Superalloy

作为航空发动机涡轮工作叶片的主要材料,镍基单晶高温合金凝固过程中的元素偏析易造成组织的不均匀性,进而影响其高温力学性能。选取国产二代单晶高温合金DD5作为研究对象,以3mm/min的抽拉速率制备单晶试棒,通过组织观察与热力学计算确定其铸态组织的相组成,包括γ相,γ’相与碳化物。采用电子探针显微分析对合金元素在枝晶干与枝晶间的偏析行为进行了线扫描,确定Re、W的正偏析及Al、Ta负偏析特性,且枝晶间的碳化物中Ta含量较高,推测其为MC型碳化物。在此基础上借助Micress相场软件,对凝固过程的组织形貌演化与元素偏析行为进行了模拟,其形貌特征与光镜组织观察结果相一致,元素分布与EPMA结果相符。

Nickel-base single crystal superalloy is frequently used for the turbine blades of aero-engine.The alloying element segregation during its solidification process leads to the heterogeneity in microstructure,which could be fatal to the high temperature mechanical property.DD5is one of the second generation of domestic single crystal superalloy.A cylinder specimen was withdrawn by a rate of3mm/min.Microstructure observation and thermodynamic calculation reveals the cast microstructure includesγ,γ'and carbide.Electron probe microanalysis was employed for the measurement of alloying element segregation across the dendrites and interdendrites,indicating that Re and W tends to segregate into dendrites while Al and Ta concentration is higher in interdendritic regions.In particular,the carbide precipitation in in-terdendritic region is proven to be Ta enriched,which is supposed to be MC type carbide.On this basis,phase field simulation on the microstructure evolution and alloying element segregation during solidification is performed via Mi-cress software.The simulated microstructure is quite similar to the experimental observation,and the alloying element distribution is in accordance with EPMA measurement.