采用OM, SEM和TEM等手段, 分析了Nb/Ti 比对铸造镍基高温合金长期时效微观组织演化的影响. 结果表明, 在长期时效期间, Nb/Ti 比对γ'相形貌演化和粗化影响不大, 但对γ'相体积分数有一定影响. 初生MC中Nb/Ti 比和(Nb+Ti)/(W+Mo) 比与合金Nb/Ti 比具有很好的线性关系. 随合金Nb/Ti 比下降, 2 个比值线性下降, 使MC分解程度提高, 热稳定性降低; 但是, 2 个比值的显著改变并不能导致MC分解程度的大幅变化, 还存在其它因素对MC热稳定性具有重要影响. MC的分解程度可通过分解前后体积分数的变化来计算, 而热稳定性强弱则可由分解程度来定量表达. Nb/Ti 比降低, 晶界粗化更加严重, 晶界析出M₂₃C₆的倾向增大, 析出M₆C的倾向减小. 但是, 合金中μ相的析出演化行为并未受到Nb/Ti 比的明显影响.

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.