沉淀强化钴基单晶高温合金凝固行为的研究进展

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.