690合金腐蚀疲劳裂纹扩展研究

Corrosion Fatigue Crack Growth in Alloy 690

基于DCPD方法测量了690合金在室温空气、325℃空气和325℃除氧超纯水中的疲劳裂纹扩展速率。试验结果采用Priddle模型进行拟合分析,得到690合金在3种条件下疲劳裂纹扩展的门槛应力强度因子幅值ΔK_(th)和失稳断裂应力强度因子Kc。结果表明,高温水环境下,疲劳裂纹萌生和扩展加快,这可以用滑移-溶解机理解释;高温下,材料强度下降,ΔK_(th)和Kc也下降,高温加速了材料的疲劳断裂。SEM断口形貌表明,空气中的疲劳断口观察到明显的滑移台阶,疲劳破坏形式为穿晶断裂;高温水下的疲劳断口则同时出现穿晶和沿晶开裂,为混合型断口特征。

Fatigue crack growth rates of alloy 690 were obtained at room temperature in air, at 325 ℃in air and at 325 ℃ in deoxidized ultrapure water based on direct current potential drop（DCPD） method. Results were analyzed by Priddle model, and thus the threshold of stress intensity factor amplitude（ΔKth） and the fracture toughness（Kc） were predicted in the above conditions. Results show that fatigue crack initiation and propagation rates are both accelerated in high-temperature water environment, which could be explained by slip dissolution mechanism. Material strength is weakened by higher temperature, which decreases ΔKth and Kc; as a result fatigue crack growth rates are accelerated. Scanning electron microscopy（SEM） examination of the fatigue fracture surfaces reveals similar slipping ledges with transgranular cracks for specimens in air, and different crack surfaces with both intergranular and transgranular attack in water environment.