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本文采用交流电位法研究了一种铁基高温合金 GH36在550℃、于不同加载条件下的裂纹扩展速率,并用扫描电镜对其断裂特征进行了分析。发现裂纹扩展规律存在着一个发生疲劳和蠕变交互作用的临界应力强度因子 K_1,当裂纹尖端的应力强度因子大于该值时,降低加载频率(或增加拉保时)将显著加速疲劳裂纹扩展速率。而小于该值时,降低加载频率(或增加拉保时)对疲劳裂纹的扩展速率却几乎没有影响。对产生这种现象的原因进行了初步探讨,在本试验条件下,主要由于疲劳裂纹和“W”型蠕变裂纹的连接而加速了裂纹的扩展。
In this paper, the crack propagation rate of an iron-based superalloy GH36 at 550 ℃ under different loading conditions was investigated by AC potential method. The fracture characteristics of the GH36 were analyzed by scanning electron microscopy. It is found that there exists a critical stress intensity factor K_1 for the interaction between fatigue and creep. When the stress intensity factor at the crack tip is greater than this value, decreasing the loading frequency (or increasing the tensile strength) will significantly accelerate the fatigue crack growth rate . On the other hand, when the load frequency is lower (or the pull-up is increased), the expansion rate of the fatigue crack is almost not affected. The reasons for this phenomenon are discussed preliminarily. Under the experimental conditions, the crack propagation is accelerated mainly due to the connection of fatigue crack and “W” creep crack.