GH4700合金偏析行为及均匀化过程中元素分配的规律

Microsegregation behavior and element distribution during homogenizing in GH4700 alloy

采用热力学计算、光学显微镜(OM)、扫描电镜(SEM)、能谱分析(EDS)等方法,分析研究了GH4700合金铸锭的显微组织及元素偏析情况,并研究了均匀化温度与时间对合金元素再分配的影响规律。结果表明:GH4700合金铸锭存在严重的枝晶偏析,Nb、Ti等元素大量偏聚于枝晶间,主要的析出相为γ’相、Laves相、MC碳化物及少量的δ相,热力学计算结果与实际相符;在均匀化过程中,元素发生明显的再分配,随着温度升高和保温时间的延长,Ti、Nb元素逐渐扩散均匀,当热处理制度为1170℃×48 h时,元素偏析基本消除,有害析出相回溶,是可选的均匀化工艺。

Microstructure and element segregation of as cast GH4700 alloy were studied by means of tbermal-cale analysis, optical microscope, SEM and EDS, and the relationship between segregation parameter δ and the parameters of homogenizing treatment was examined. The results show that GH4700 alloy exhibits severe dendritic segregation, in which Nb and Ti elements are intensively segregated to the interdendritic regions, leading to the main precipitation of γ＇ phase, Laves phase, MC carbide and little δ phase, and thermodynamic calculation results are consistent with the observation. Significant redistribution of etements occurs during homogenizing. With the increase of hemogenizing temperature and holding time, Ni and Ti are gradually distributed evenly by diffusion. It is found that the segregation of lements is basically eliminated and the harmful precipitation phases are redissolved for the GH4700 alloy after homogenizing trectment at 1170 ℃ for 48 h.