(1. 长安大学材料科学与工程学院，西安 710064；
2. 西北工业大学凝固技术国家重点实验室，西安 710072)
摘 要: 沉淀强化钴基单晶高温合金具有成本低、初熔点高和抗热腐蚀性能优异等特征，是制备在热腐蚀环境下长期服役的单晶涡轮叶片的重要候选材料。本文总结了沉淀强化钴基单晶高温合金的凝固特征温度、显微偏析、凝固路径和枝晶组织等凝固行为，并与典型镍基单晶高温合金的凝固行为进行了对比。Ta、Ti和Nb元素的添加显著地降低了固相线温度和液相线温度，并扩大了结晶温度区间，而Cr、V、Mo和Ni元素对凝固特征温度的影响较小。凝固时Al、Ta和Ti元素偏析于枝晶间区域，W元素偏析于枝晶干区域，Cr和Ni元素的显微偏析倾向较弱。同时，含Ta/Ti的钴基单晶高温合金在凝固末期形成了多种枝晶间析出相，导致合金具有较复杂的凝固路径。此外，与镍基单晶高温合金类似，定向凝固时冷却速率和合金成分特征均影响了钴基单晶高温合金的一次枝晶间距。
关键字: 钴基单晶高温合金；沉淀强化；凝固特征温度；显微偏析；凝固路径；枝晶组织
（1. School of Materials Science and Engineering, Chang''an
University, Xi''an 710064, China;
2. State Key Laboratory of Solidification
Processing, Northwestern Polytechnical University, Xi''an 710072, China）
Abstract:As an important candidate material for the preparation of single crystal turbine blades in long-term service under thermal corrosion environment, the γ'''' strengthened cobalt-based single crystal superalloys occupy the characteristics of low cost, high initial melting point, excellent thermal corrosion resistance, et al. This paper summarized the solidification behaviors of γ'''' strengthened cobalt-based single crystal superalloys, such as the solidification characteristics temperatures, microsegregation behavior of alloying elements, solidification path and dendritic microstructure, and compared with those of typical Ni-based single crystal superalloys. The additions of Ta, Ti and Nb significantly decrease the solidus and liquidus temperatures and expand the solidification range of cobalt-based single crystal superalloys. However, Cr, V, Mo and Ni elements have less effect on the solidification characteristics temperatures. During solidification, Al, Ta and Ti elements segregate to interdendritic region, W element segregates to dendritic core, and the microsegregation degrees of Cr and Ni elements are relatively weak. Due to the severe microsegregation of Ta and Ti elements, various interdendritic precipitations with relatively high Ta/Ti contents form at the last stage of solidification, which complicates the solidification paths of cobalt-based single-crystal superalloys. Finally, similar to Ni-based single crystal superalloys, the as-cast dendritic microstructure of γ'''' strengthened cobalt-based single crystal superalloys is refined with increasing cooling rate and content of high refractory elements.
Key words: γ'' strengthened cobalt-based single crystal superalloy; solidification characteristics temperature; microsegregation behavior; solidification path; dendritic microstructure
