Evolution of TCP Phase During Long Term Thermal Exposure in Several Re-Containing Single Crystal Superalloys

doi:10.1007/s40195-019-00976-2

Abstract

Abstract:

The application and component designs of single crystal superalloys are restricted by the precipitation of topologically closed packed (TCP) phases, which can deteriorate the microstructural stability of the alloys severely. Limited researches concerning the type and morphology evolution of TCP phases under elevated temperature conditions have been reported previously. In the present work, three Re-containing single crystal alloys were designed to investigate TCP phase evolution via long term isothermal exposure tests at 1120 °C while the effects of Re on the microstructural characteristic and elements segregation were also clarified. The results showed that the addition of Re increased the instability of the alloys and the volume fraction of the TCP phases exceeded 5 vol% when the Re content reached 3 wt%. The increasing Re content had also raised the precipitation temperature of TCP phases but it did not change the type of them after long term aging; all the TCP particles were identified as μ phase in this study. Moreover, the elements segregation became considerably serious as Re addition increased constantly, which brought about various morphologies of the μ phase in the experimental alloys. In particular, the rod-like and needle-like μ phases demonstrated the typical orientation within γ matrix while the blocky μ phase was dispersedly distributed in the space. No specific orientation relationship could be observed in the μ phase when the addition of Re exceeded certain threshold value.

Key words: Single crystal superalloys, Topologically closed packed (TCP) phase, Re, Elements segregation, Morphology

Zihao Tan, Lin Yang, Xinguang Wang, Yunling Du, Lihua Ye, Guichen Hou, Yanhong Yang, Jinlai Liu, Jide Liu, Jinguo Li, Yizhou Zhou, Xiaofeng Sun. Evolution of TCP Phase During Long Term Thermal Exposure in Several Re-Containing Single Crystal Superalloys[J]. Acta Metallurgica Sinica (English Letters), 2020, 33(5): 731-740.

Figures/Tables 12

Table 1 Chemical composition of the three experimental single crystal superalloys (wt%)

Fig. 1 Morphologies of the experimental alloys: a as-cast structure, b heat-treated structure

Fig. 2 SEM images of Alloy 1Re after long term aging at 1120 °C with different time: a 100 h, b 200 h, c 500 h, d 1000 h

Fig. 3 SEM images of Alloy 2Re after long term aging at 1120 °C with different time: a 100 h, b 200 h, c 500 h, d 1000 h

Fig. 4 SEM images of Alloy 3Re after long term aging at 1120 °C with different time: a 100 h, b 200 h, c 500 h, d 1000 h

Table 2 Volume fraction of the μ phase in three experimental single crystal superalloys

Fig. 5 Bright TEM images and SADP of the μ phase in three experimental alloys after 1000 h aging at 1120 °C: a, d Alloy 1Re, b, e Alloy 2Re, c, f Alloy 3Re

Table 3 Primary composition of the μ phase in the three single crystal superalloys after 1000 h aging at 1120 °C (at%)

Fig. 6 Equilibrium phase diagrams of the experimental alloys by thermal-calc software: a Alloy 1Re, b Alloy 2Re, c Alloy 3Re

Fig. 7 Effects of Re on the elements distribution in the three experimental alloys: a segregation ratio, b partition coefficient

Fig. 8 Schematic illustration of possible precipitate behavior of the μ phase at early stage in the three experimental single crystal alloys

Fig. 9 Schematic illustration of possible final morphologies of the μ phase in the three experimental single crystal alloys

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