Under asymmetrical stress-controlled cyclic loading accompanied by ratcheting, the evolution of microscopic substructures of stainless steel 304 (SS304), a face-centered cubic metal, was detected using transmission electron microscopy (TEM). This observation demonstrates that dislocation slip is the main mechanism of uniaxial ratcheting in the non-steady stage (stage I). Dislocation proliferate rapidly duo to the high stress level of the cyclic tests, and dislocation density increases continuously with the the number of cycles. The ratcheting rate decreases continuously due to the interaction of moveable dislocations, and the planar dislocation substructures (dislocation pileups and tangles) are the dominant patterns in this stage. In the later stage I, distinct lath $$\alpha $$ -martensite was observed in the material due to the nucleation of martensite and the phase transformation zones increase gradually with the growth of axial ratcheting strain in the stage II of uniaxial ratcheting. The multiply and cross-slip were activated gradually in increasing numbers of grains, and the prevailing dislocation configurations evolve into more complicated and stable ones (dislocation walls and cells). In addition the dislocation configurations after various prescribed tensile strain of the monotonic tension and creep deformation with three different holding times were also observed by TEM. Comparing the evolution of microscopic substructures in various loading modes, the physical mechanism of uniaxial ratcheting of SS304 can be revealed as combination of the evolution of dislocation configurations and martensite transformation in the stage II of uniaxial ratcheting.

中文翻译：

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发生单轴棘轮变形的 304 不锈钢微观子结构

在伴随棘轮的不对称应力控制循环载荷下，使用透射电子显微镜 (TEM) 检测到不锈钢 304 (SS304)（一种面心立方金属）的微观亚结构的演变。这一观察表明，位错滑动是非稳态阶段（阶段 I）中单轴棘轮的主要机制。由于循环试验的高应力水平，位错迅速增殖，位错密度随着循环次数的增加而不断增加。由于可动位错的相互作用，棘轮速率不断降低，平面位错亚结构（位错堆积和缠结）是该阶段的主要模式。在后期我，由于马氏体形核，材料中观察到明显的板条$$\alpha $$ -马氏体，在单轴棘轮第二阶段，随着轴向棘轮应变的增长，相变区逐渐增加。随着晶粒数量的增加，倍增和交叉滑移逐渐被激活，占主导地位的位错构型演变为更复杂和稳定的位错构型（位错壁和位错胞）。此外，透射电镜还观察到了三种不同保持时间的单调拉伸和蠕变变形的各种规定拉伸应变后的位错构型。比较各种加载模式下微观子结构的演变，