镍基双晶高温合金定向凝固过程中的竞争生长

来源期刊：金属学报2011年第6期

论文作者：卢琦 李金国 金涛 周亦胄 孙晓峰 胡壮麒

文章页码：641 - 648

关键词：高温合金； 定向凝固； 竞争生长； 枝晶生长

Key words：superalloy； directional solidification； competitive growth； dendrite growth

摘    要：研究了镍基双晶高温合金定向凝固过程中的竞争生长.实验结果表明:当原始籽晶一次枝晶方向均平行于热流方向且二次枝晶取向不同时,定向凝固过程中双晶共存,但双晶的界面存在波动,抽拉速率对其影响不大.当原始籽晶一次枝晶([001])异面并保持其中一组二次枝晶取向([010])相同时,双晶竞争生长过程是一个三维竞争生长过程.晶粒竞争生长从3个方向同时进行,择优取向晶粒通过螺旋状生长方式淘汰非择优取向晶粒,双晶竞争生长过程与抽拉速率密切相关,随着抽拉速率的增加,择优取向晶粒淘汰非择优取向晶粒的速率加快.

Abstract: Single crystal nickel-based superalloys,which offer improved creep-rupture,fatigue, oxidation and coating properties,have been widely applied in turbine blades and vanes.In general, the single crystal structure is produced through competitive grain growth by directional solidification technology.However,in actual directional solidification process,the orientations of the primary and secondary dendrites are random due to the randomness of the grain nucleation.Therefore,the actual competitive grain growth during directional solidification is a three-dimensional process.However the related literatures are fewer.In the present study,an experimental study had been conducted to investigate the three-dimensional competitive grain growth behavior under different withdrawal velocities by the bi-crystal samples with special orientation relationships.The results showed that the whole sample with bi-crystal microstructure could be obtained when the two seeds were with the same primary dendrites orientation paralleled to the heat flow direction but different orientations of the secondary dendrites.And the withdrawal velocity had little influence on the competitive grain growth in this disposition relationship.However,only the favorably oriented grain could be obtained when the two seeds were with the non-coplanar primary dendrites and a group of secondary dendrites with the same orientation.The favorably oriented grain overgrew the misaligned grain in a heliciform way.And the overgrowth velocity was in direct proportion to the withdrawal velocity.