定向凝固镍基高温合金DZ125平界面生长的微观组织演化

MICROSTRUCTURAL EVOLUTION OF DIRECTIONALLY SOLIDIFIED Ni-BASED SUPERALLOY DZ125 UNDER PLANAR GROWTH

采用液态金属冷却(LMC)定向凝固技术,对镍基高温合金DZ125在凝固速率为1.5μm/s的条件下其平界面生长的微观组织演化规律进行了研究.结果表明:凝固组织演化经历3个不同的阶段,当凝固分数f_s≤0.26时,为单相γ组织,基体中零星分布着细小的颗粒状的未熔HfC;当0.26<f_s<0.86时,为γ/MC共生组织,MC为纤维状或者板片状;当f_s≥0.86时,为γ/γ′共晶组织和分布于其中的粗大块状MC.EPMA结果表明:Al,Ti,Ta和Mo含量随f_s的增大而增大;而W,Cr和Co含量随f_s的增大而减小.分析指出,凝固组织转变是由于溶质再分配产生的宏观溶质分布不均匀造成的.

By using liquid metal cooling method,the Ni-based superalloy DZ125 was directionally solidified under planar interface growth condition of drawing rate of 1.5μm/s.The microstructures at different solidified fractions were examined by OM and SEM.The results showed that the solid/liquid interface is planar and the microstructure evolution undergoes three stages：theγphase was formed as solidified fraction（f_s） was not more than 0.26,and the fine HfC phase sparsely distributed inγmatrix;the coupledγ/MC growth appeared as f_s ranged from 0.26 to 0.86,and the morphology of MC was fibrous or plate-like shapes;theγ/γ＇ eutectic was obtained as f_s was more than and equaled 0.86 0.86,in which the octahedral MC was precipitated simultaneously.EPMA was used to determine the solute distribution along the longitudinal direction of the sample.The contents of Al,Ti,Ta and Mo increased with f_s increasing,while the contents of W,Cr and Co decreased.The analysis showed that the microstructure transformation is attributed to macro-scale non-uniform solute distribution which resulted from solute redistribution during directional solidification.