316L不锈钢非比例路径疲劳失效的微观机理

进行316L不锈钢在600℃圆路径下不同应变范围的低周疲劳实验，用透射电子显微镜(TEM)观察疲劳失效断口附近的显微组织，研究了位错结构的路径相关性、幅值相关性以及动态应变时效(Dynamic strain aging,DSA)的路径相关性。结果表明：在室温和600℃的单轴加载变形以平面滑移方式为主，生成了脉络状位错结构；而在圆路径下则生成等轴胞状位错结构，显著降低了材料抵抗变形的能力，在600℃等效应变范围为1.0%条件下的疲劳寿命比单轴路径降低了81%。同时，在圆路径下材料形成胞状位错结构所需最小等效应变范围比单轴的低。600℃圆路径下的DSA效应更为完全，在等效应变范围为1.0%的条件下最大应力跌幅比单轴路径增大了680%；同时，压缩阶段的DSA现象更为显著，锯齿类型由A型经过B型过渡到C型。

Micromechanism of Fatigue Failure under Non-proportional Loading for 316L Stainless Steel

Low cycle fatigue experiments for 316L stainless steel were carried out under circular loading and different strain ranges at 600℃. The microstructures near the fatigue fracture were observed by transmission electron microscope (TEM). The path correlation and amplitude correlation of dislocation structure and the path correlation of dynamic strain aging (DSA) were investigated based on the experimental results. The results show that at room temperature and 600℃, the planar slip is significant under uniaxial loading and the choroid dislocation structure formed. However, the equiaxed cellular dislocation structures are exhibited under circular loading, which reduces the deformation resistance of the material significantly. For equivalent strain range 1.0%, the fatigue life under circular loading is 81% lower than that of the uniaxial loading at 600℃. At the same time, the minimum equivalent strain range required to form a cellular dislocation structure under the circular loading is lower than that of the uniaxial loading. At 600℃, the DSA effect is more complete under circular loading, and the maximum stress drop for equivalent strain range 1.0% increases by 680% compared with that under uniaxial loading. The DSA phenomenon is more evident in the compression stage, and the sawtooth type gradually transitions from type A, type B to type C.