N18锆合金的低周疲劳行为

在不同试验温度（室温～500℃）下，对N18合金进行了低周疲劳试验。试验结果表明：室温～300℃温区，合金表现为明显的循环软化；400、450℃时，合金逐渐呈现循环硬化，450℃时其硬化现象更为明显；500℃时则主要表现为循环饱和。随着温度的升高，疲劳寿命先增加后降低，300℃时疲劳寿命最高。低应变幅下，温度对疲劳寿命的影响更明显。通过疲劳断口SEM分析，室温下疲劳起源于单个裂纹源，疲劳裂纹扩展阶段的微观特征主要是疲劳条纹，局部区域出现轮胎状花样。在高温下为多裂纹源，大量二次裂纹的存在是高温疲劳断口的主要特征。

Low Cycle Fatigue Behavior of N18 Alloy

Low cycle fatigue (LCF) tests were conducted on N18 alloy at different temperatures varying from room temperature to 500 ℃. The results show that N18 alloys display cyclic softening from room temperature to 300 ℃. When the temperature is 400 and 450 ℃, the alloy presents the cyclic hardening gradually; at 450 ℃, its hardening phenomenon is more obvious. Saturation stage occupies the majority of the entire cycle fatigue life at 500 ℃. The fatigue life increases as the temperature increases, then the fatigue life decreases, LCF life shows a maximum at 300 ℃, and the temperature effect on life is more pronounced at low strain amplitudes. The analysis of the fracture surface reveals fatigue cracks originated in a single source at room tempera-ture, on the fatigue crack propagation' s stage, micro-feature is mainly the fatigue stripe, and the local region presents the tire-like pattern. However, at high tempera-ture, there are multiple crack sources, the fracture is characterized by secondary cracks.