定向凝固DZ125合金的溶质分配系数及偏析行为的研究

来源期刊：金属学报2010年第12期

论文作者：闵志先 沈军 冯周荣 王灵水 刘林 傅恒志

文章页码：1543 - 1548

关键词：镍基高温合金； 溶质分配系数； 偏析； 定向凝固

Key words：Ni-based superalloy； solute partition coefficient； segregation； directional solidification

摘    要：采用定向凝固技术结合液淬法对DZ125合金平界面和枝晶生长条件下溶质的偏析行为进行了研究,通过EPMA定量测定γ基体中各元素的溶质含量和淬火平界面两侧固相和液相中的溶质含量,分别获得了溶质再分配后固相中的溶质分布状态及溶质分配系数.结果表明,平界面生长条件下,液相中的熔体流动使溶质再分布始终处于非稳态.Al,Ti,Ta,Mo和Ni元素的溶质分配系数小于1;而W,Cr和Co元素的溶质分配系数大于1,溶质分布状态满足Scheil模型.枝晶与平界面生长的溶质偏析行为基本一致,然而,固相反扩散显著降低了枝晶生长过程中的溶质偏析.

Abstract: Segregation behavior is an important problem in solidification process of alloys,which determines their growth morphologies,phase distributions and concentration segregations so that it affects the mechanical properties of alloys,such as fatigue lives,creep properies,etc..However,the segregation behaviors of Ni-based superalloys are very complex that contain multi-components and consist of multi-phases.The solute partition coefficient is a key characteristic parameter to express the solute segregation level and tendency in a solidification process.In the present paper,the solute profiles in directionally solidified DZ125 alloy with planar interface growth,which was obtained through experiments of quenching during directional solidification,have been measured by electron probe micro analysis (EPMA).The steady state of solute redistribution hardly reaches due to melt flow during solidification process.The contents of γ′ phase forming elements,Al,Ti,Ta,Mo and Ni,along longitudinal direction increase with the increase of solidified fraction,while those of W,Cr and Co decrease.The results show that the solute partition coefficients of Al,Ti,Ta,Mo and Ni are less than unit,those of W,Cr and Co are more than unit.In addition,the solute distribution in solid phase with dendrite growth is similar to that with planar interface growth.Compared the experimental results of microsegregation with the calculated ones of Scheil model and Brody-Flemings model,the Brody-Flemings model fits better with the experimental results.It indicates that the back-diffusion in solid phase would reduce the microsegregation during dendrite growth.