The effect of Co on element segregation and microstructure is investigated in the third generation Ni-based single crystal superalloys with 4, 8.5, and 11.5 wt% Co addition. The results show that the increase of Co content leads to a severe element segregation in as-cast microstructure. After heat treatment, the size of γ′ phase is slightly reduced with Co content increase. During the thermal exposure, the γ′ phase coarsens gradually but its coarsening rate decreases with increasing Co content. In addition, some acicular and blocky topologically close-packed (TCP) phases are precipitated in 4% Co and 8.5% Co alloys. However, no TCP phase can be found in 11.5% Co alloy. Finally, it may be concluded that although a higher Co content is harmful for the element segregation, it is beneficial to maintain the cuboidal morphology of γ′ phase, decrease its coarsening rate, and impede the precipitation of TCP phase.
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This work was supported by the National High Technology Research and Development Program of China (2012AA03A511), the State Key Program of National Natural Science of China (51331005), the Natural Science Foundation of Shaanxi Province (2014JM622), the NWPU Foundation for Basic Research (3102014JCQ01022), and the Advanced Aeroengine Collaborative Innovation Center of China.
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Wang, B., Zhang, J., Huang, T. et al. Effect of Co on microstructural stability of the third generation Ni-based single crystal superalloys. Journal of Materials Research 31, 1328–1337 (2016). https://doi.org/10.1557/jmr.2016.98