Influence of oxidation on fatigue crack initiation and propagation in turbine disc alloy N18
Influence of oxidation on fatigue crack initiation and propagation in turbine disc alloy N18
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DOI：
10.1016/j.ijfatigue.2015.02.007
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发表时间：
2015-06-01
影响因子：
6
通讯作者：
Reed, P. A. S.
中科院分区：
文献类型：
--
作者：
Jiang, R.;Everitt, S.;Reed, P. A. S.
在650 ℃和725 ℃的空气和真空条件下，在三点加载条件下，对亚固溶线热处理的涡轮机盘合金N18的疲劳裂纹萌生和扩展行为进行了评估。疲劳裂纹萌生过程已使用单边U形切口试样在1-1- 1-1梯形加载波形下进行评价，沿着在650 ℃下进行间断试验，以允许间断观察切口表面。结果表明，在氧分压为10（-2）~ 10（-3）Pa时，合金发生明显的晶界氧化。由于富Cr和/或富Co氧化物的形成和随后的开裂，裂纹主要从晶界或γ/γ '界面开始，偶尔从表面孔隙开始。在这些测试中的疲劳寿命似乎是由这个裂纹萌生过程，并显着降低通过增加温度和/或应用的氧化环境。在1-1-1 -1和1-20-1-1加载波形下进行的裂纹扩展试验表明，氧化显著降低了N18的裂纹扩展阻力，并与更多的沿晶断裂表面特征相关。由较高温度或延长停留时间引起的对扩展的额外氧化作用似乎有限，而延长的停留时间似乎反而促进额外的蠕变过程，这进一步增强裂纹生长，特别是在较高温度下。(C)2015爱思唯尔有限公司版权所有。
Fatigue crack initiation and propagation behaviour in subsolvus heat treated turbine disc alloy N18 has been assessed in air and vacuum at 650 and 725 degrees C under three-point loading. Fatigue crack initiation processes have been evaluated using single edge U-notch specimens under a 1-1-1-1 trapezoidal loading waveform along with interrupted tests at 650 degrees C to allow intermittent observations of the notch surface. The results show apparent grain boundary (GB) oxidation can occur under an oxygen partial pressure of 10(-2)-10(-3) Pa. Cracks mainly initiate from grain boundaries or gamma/gamma' interfaces due to the formation and subsequent cracking of Cr-rich and/or Co-rich oxides, and occasionally initiate from surface pores. Fatigue life in these tests appears to be dominated by this crack initiation process and is significantly reduced by increasing temperature and/or application of an oxidizing environment. Crack growth tests conducted under 1-1-1-1 and 1-20-1-1 loading waveforms indicate that oxidation significantly degrades the crack growth resistance of N18 and is associated with more intergranular fracture surface features. Additional oxidation effects on propagation caused by higher temperature or prolonging dwell time appear limited, whereas a prolonged dwell period seems to instead promote additional creep process, which further enhance crack growth, especially at higher temperature. (C) 2015 Elsevier Ltd. All rights reserved.