镍基单晶高温合金凝固偏析的表征方法比较

Comparison of Characterization Methods for Solidification Segregation of Ni-based Single-crystal Superalloy

分别采用金相、差热分析、枝晶干/枝晶间取点和随机点阵等方法,对一种含Ru镍基单晶高温合金的凝固偏析进行了表征。结果表明:通过金相和差热分析技术可以对凝固偏析进行定性地表征;同样,采用枝晶干/枝晶间取点法可以定量表征凝固偏析,但铸态组织的不均匀性会给结果带来较大误差;采用点阵法,可以随机地选择测试区域,并通过Scheil方程拟合分凝系数,由于测试过程中干扰因素较少,结果具有较高的可靠性;在凝固过程中,Re和W元素强烈地偏析于枝晶干,Al和Ta元素偏析于枝晶间,而Ru和Co元素偏析程度很低。

The solidification segregation of a Ni-based single-crystal superalloy containing Ru was characterized by using metallography,differential thermal analysis,dendritic trunk/inter dendritic sampling points and random point matrix.The results show that the solidification segregation can be qualitatively characterized by metallography and differential thermal analysis.In the same way,the solidification segregation can be quantitatively characterized by adopting the dendrite trunk/inter dendritic sampling points method,but the inbomogeneity of as-cast structure will bring great error to the results. Using the point matrix method,the test area can be randomly selected,and the segregation coefficient can be fitted by the Scheil equation.As the interference factor in the testing process is small,the result has higher reliability.In the solidification process,the elements of Re and W are strongly segregated in the dendrite trtmk,Al and Ta elements are segregated in inter dendritic,but the segregation degree of Ru and Co is very low.