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Oxygen enhanced crack growth in nickel-based superalloys and materials damage prognosis

机译：氧增强镍基高温合金的裂纹扩展和材料损坏的预后

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This paper summarizes the results from a comprehensive multidisciplinary study to better understand the role of niobium and other strengthening elements in enhancing crack growth by oxygen in nickel-based superalloys at high temperatures, and considers its importance for materials damage prognosis and life cycle engineering in high temperature service. Three gamma' strengthened powder metallurgy (P/M) alloys, with 0, 2.5 and 5 wt pct Nb and comparable volume fractions (about 53 vol pct) of gamma" precipitates, were specially designed for this study. Coordinated crack growth, microstructural and surface chemistry studies were conducted on the alloys. They were complemented by oxidation studies of Nb, Ni_3Nb, NbC, Ni_3Al and Ni_3Ti, and analyses of fracture surfaces of interrupted crack growth specimens by X-ray photoelectron spectroscopy (XPS). The findings taken in toto show that oxygen enhancement of crack growth is the result of the formation of a brittle film of surface oxides along grain boundaries and interfaces ahead of the crack tip by the preferential oxidation of Nb, Ti and Al in the Nb-rich carbides and Ni_3Al, Ni_3Ti and Ni_3Nb (in Inconel 718) precipitates. The results also showed that the oxidation of Nb-rich carbides alone can significantly enhance crack growth in oxygen. The findings are discussed in relation to the previously proposed crack growth mechanisms, and their applications.
机译：本文总结了一项综合的多学科研究的结果，以更好地理解铌和其他强化元素在高温下镍基高温合金中氧促进裂纹扩展中的作用，并考虑了其对高温下材料损伤预后和生命周期工程的重要性。温度服务。本研究专门设计了三种γ'增强粉末冶金（P / M）合金，分别具有0、2.5和5 wt％的Nb和可比较的体积分数（约53 vol pct）的γ“沉淀物。对合金进行了表面化学研究，并辅之以Nb，Ni_3Nb，NbC，Ni_3Al和Ni_3Ti的氧化研究，以及通过X射线光电子能谱（XPS）分析中断的裂纹扩展试样的断裂表面。 toto表明，裂纹扩展的氧气增强是由于富Nb的碳化物和Ni_3Al中Nb，Ti和Al的优先氧化而沿裂纹边界前方的晶界和界面形成了表面氧化物脆性膜的结果， Ni_3Ti和Ni_3Nb（在Inconel 718中）析出，结果还表明，仅富Nb的碳化物的氧化可以显着增强氧气中的裂纹扩展。先前提出的裂纹扩展机制及其应用。

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