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研究了GH864合金不同保载时间下650℃蠕变/疲劳裂纹扩展行为,分析了裂纹扩展过程中蠕变和氧化的作用,以及a-N曲线的转折点含义。结果表明:保载5s时GH864合金以穿晶断裂为主,疲劳作用占主导;保载90s时GH864合金以沿晶断裂为主,蠕变作用占主导。利用Saxena模型可较好地表征本实验条件下650℃蠕变/疲劳交互作用的裂纹扩展速率曲线,可估算较高应力强度因子和较低应力强度因子的裂纹扩展速率。另外,用Saxena模型可求出蠕变和疲劳的表达式,对比分析高温蠕变/疲劳交互作用的裂纹扩展过程中蠕变和疲劳的作用及所占的比例。最后针对a-Ni/Nf、da/dN-a曲线及da/dN-N曲线变换中出现的拐点,结合断口形貌分析了转折点对应的含义。高温合金及其它材料的裂纹扩展速率曲线也适用于以上曲线分析方法。
The creep / fatigue crack growth behavior at 650 ℃ for different holding time of GH864 alloy was studied. The effects of creep and oxidation during crack growth and the inflection point of a-N curve were analyzed. The results show that GH864 alloy is predominantly transgranular, and the fatigue is the dominant one. The creep effect of GH864 alloy is dominant at 90s. The Saxena model can be used to characterize the crack growth rate curve of 650 ℃ creep / fatigue interaction under this experimental condition, and the crack growth rate of higher stress intensity factor and lower stress intensity factor can be estimated. In addition, expressions of creep and fatigue can be obtained by using the Saxena model, and the role of the creep and fatigue in the crack propagation process at high temperature creep / fatigue interaction and its proportion are analyzed and compared. Finally, according to the inflection points appearing in the curves a-Ni / Nf, da / dN-a and da / dN-N, the corresponding meanings of turning points are analyzed according to the fracture morphology. Crack propagation rate curves for superalloys and other materials also apply to the above curve analysis method.