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EFFECTS OF Nb/Ti RATIOS ON THE MICROSTRUCTURAL EVOLUTIONS OF CAST Ni-BASED SUPERALLOYS DURING LONG-TERM THERMAL EXPOSURE |
SUN Wen1,2, QIN Xuezhi2, GUO Yongan2, GUO Jianting2, LOU Langhong2, ZHOU Lanzhang2 |
1 University of Science and Technology of China, Hefei 230022 2 Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016 |
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Cite this article:
SUN Wen, QIN Xuezhi, GUO Yongan, GUO Jianting, LOU Langhong, ZHOU Lanzhang. EFFECTS OF Nb/Ti RATIOS ON THE MICROSTRUCTURAL EVOLUTIONS OF CAST Ni-BASED SUPERALLOYS DURING LONG-TERM THERMAL EXPOSURE. Acta Metall Sin, 2014, 50(6): 744-752.
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Abstract Effects of Nb/Ti ratios on the microstructural evolutions of cast Ni-based suerpalloys during long-term thermal exposure are investigated by OM, SEM and TEM. The results show that Nb/Ti ratios have no influence on the evolution of γ? morphology and size during long-term thermal exposure. However, with decrease of Nb/Ti ratios in alloys, the volume fraction of γ? phase increases. Both parameters Nb/Ti and (Nb+Ti)/(W+Mo) of primary MC have a good linear relationship with Nb/Ti ratios in alloys. With decrease of Nb/Ti ratios in alloys, both parameters for primary MC linearly decrease and sequentially thermal stability of primary MC is weakened. However, the results also show that Nb/Ti and (Nb+Ti)/(W+Mo) ratios of primary MC are not the principle factors determining the thermal stability of primary MC. The degeneration degree of primary MC can be calculated by the volume fraction of primary MC before and after degeneration, while the thermal stability of primary MC can be quantitatively characterized by degeneration degree of primary MC. Furthermore, with decreased Nb/Ti ratios in alloys, the grain boundaries coarsen more severely during long-term thermal exposure. Meanwhile, precipitation tendency of M23C6 carbide on grain boundaries increases and that of M6C carbide on grain boundaries decreases. However, the precipitation and evolution of μ phase during long-term thermal exposure is not affected by Nb/Ti ratios obviously.
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Received: 17 January 2014
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Fund: Supported by National Natural Science Foundation of China (No.51001101) |
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