镍基单晶高温合金晶体取向的选择及其控制

Influence of Crystal Orientation on Microstructure and Mechanical Properties and Its Control for Nickel-Base Single Crystal Superalloys

镍基单晶高温合金是航空发动机和燃气轮机叶片的重要材料,该合金具有<001>的择优取向。回顾了镍基单晶高温合金晶体取向与单晶铸件高温力学性能的关系,不同取向单晶的高温拉伸性能、抗蠕变、低周疲劳等性能均明显不同。<001>方向具有较高的综合力学性能。结合作者在本领域的研究,发现不同取向的枝晶生长规律不同,<011>取向的枝晶在纵截面上枝晶干呈"V"或"W"形状,横截面上枝晶干呈直线排列,同时不同取向的枝晶间距和溶质元素偏析程度不同。总结了选晶过程中引晶段和螺旋段在单晶制备中的作用,晶体取向决定于引晶段的选晶效果,螺旋段的主要作用为确保获得单一的晶粒;分析了籽晶法单晶制备过程中晶体取向对晶体生长的影响及造成取向偏离的一些因素。展望了镍基单晶高温合金晶体取向的研究发展方向。

Nickel-based single superalloys are important materials for blades in aero-engines and land based gas turbine for its excellent high temperature strength. It has been established that nickel-base superalloys preferentially grow along 〈 001 〉 orientation. This paper summarizes the influence of crystal orientation on the mechanical properties of nickel-based single crystal superalloys castings. The tensile properties, creep life and low cycle fatigue （LCF） are depend on crystal orientation. Single crystals with 〈OO1 〉 orientations have optimized high temperature mechanical properties. Based on the author＇s research features in the field, dendrites in the longitudinal section for the crystals with 〈011 〉 orientation showed ＂V＂ and ＂W＂ patterns, while the primary dendrites in the transverse section aligned in lines. Meanwhile, the dendrite arm spacings and microsegregation of elements along different orientations are obviously different. The main function of starter block of spiral grain selector is to optimize the crystal orientation, and the spiral part is to ensure that only one grain can be obtained. Furthermore, we include some influencing factors related to the misorientation and the crystal growth for the seeding technology. Finally, we discussed the possible development trends of the crystal orientation in future.