应变幅和保持时间对C-276合金低周疲劳寿命的影响

研究了保持时间和应变幅对C-276合金650℃下的低周疲劳寿命的影响。测试中采用应变幅为0.3%,0.35%,0.4%,0.45%和0.5%,保持时间为0,30和60s的梯形波轴向总应变控制疲劳实验,并利用扫描电镜(SEM)观察了合金在各实验条件下的断口特征。结果表明,在同一保持时间下,随着应变幅的增加,裂纹扩展速率增大,疲劳寿命降低。而保持时间的引入对疲劳寿命的影响则与应变幅的大小有关:在较低的应变幅(0.35%~0.4%)下,引入保持时间,造成疲劳裂纹扩展速率增大,并且有微裂纹和空洞形成,在两者的共同作用下使疲劳寿命降低;在较高的应变幅(0.45%~0.5%)下,引入保持时间,造成微裂纹和空洞的焊合,使疲劳寿命不降反升。

Effects of Total Strain Range and Dwell Time on Low Cycle Fatigue Life of C-276 Alloy

The effects of total strain range and dwell time on low cycle fatigue life of C-276 alloy at 650 °C were investigated. The total strain range controlled fatigue tests were performed at total strains of 0.3%, 0.35%, 0.4%, 0.45% and 0.5% with dwell time of 0, 30 and 60 s respectively. The fracture characteristics were observed by SEM. Results show that the fatigue life significantly decreases with increasing the total strain range for the fixed dwell time due to the enhanced fatigue crack-growth-rate. The effect of dwell time on the fatigue life is dependent on the introduced total strain range. In lower total strain range of 0.35%~0.4%, the fatigue life is decreased by introducing dwell time, which is obviously caused by the coeffect of the enhanced fatigue crack-growth-rate and the presence of some microcracks and cavities. In higher total strain range of 0.45%~0.5%, the fatigue life is increased by introducing dwell time due to the closed microcracks and cavities