CAJ | 학술논문

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.
재불동시험온도(실온～500℃)하,대N18합금진행료저주피로시험.시험결과표명:실온～300℃온구,합금표현위명현적순배연화;400、450℃시.합금축점정현순배경화,450℃시기경화현상경위명현;500℃시칙주요표현위순배포화.수착온도적승고,피로수명선증가후강저,300℃시피로수명최고.저응변폭하,온도대피로수명적영향경명현.통과피로단구SEM분석,실온하피로기원우단개렬문원,피로렬문확전계단적미관특정주요시피로조문,국부구역출현륜태상화양.재고온하위다렬문원,대량이차렬문적존재시고온피로단구적주요특정.
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.