Aiming to investigate the dependency of hydrogen-affected fatigue crack growth (HAFCG) on the loading frequency f, this study experimentally characterized the HAFCG in a commercially pure iron as a function of f ranging from 0.02 to 20 Hz as well as a stress intensity factor range ΔK and hydrogen gas pressure \( P_{{{\text{H}}_{2} }} \). The crack tip plasticity was analyzed by interferometric microscopy and transmission electron microscopy in addition to the fracture surface observation. As a result, the amount of FCG rate acceleration by hydrogen increases as f decreases until it reaches a critical value (f = 2 Hz at \( P_{{{\text{H}}_{2} }} \) = 3.5 MPa, f = 0.2 Hz at \( P_{{{\text{H}}_{2} }} \) = 35 MPa), while the HAFCG rate greatly decreases once f decreases below the critical value. At the same time, the fracture mode at \( P_{{{\text{H}}_{2} }} \) = 3.5 MPa changes from brittle quasi-cleavage to a more ductile manner showing no clear hydrogen influence. On the other hand, the size of cleavage-like facets becomes large in case of \( P_{{{\text{H}}_{2} }} \) = 35 MPa suggesting that the number of lattice planes causing cleavage is reduced because of less hydrogen effect. The crack tip plasticity reduction by hydrogen is clearly confirmed while the HAFCG enhancement occurs above the critical value of f. In contrast, at f below the critical value, the crack tip plasticity is recovered to almost the same level as in the inert environment. Based on a theoretical estimation of hydrogen diffusion from the crack tip, the critical value of f causing this reversal f dependency is likely determined by the hydrogen concentration gradient in the vicinity of the crack tip. Although the associated mechanism is still unclear, it is suggested that the dynamic interaction between mobile dislocations and diffusing hydrogen atoms is important in clarifying the mechanism of HAFCG.

为了研究氢影响的疲劳裂纹扩展（HAFCG）对载荷频率f的依赖性，本研究通过实验对商用纯铁中的HAFCG随f在0.02至20 Hz之间的变化以及应力强度因子进行了表征。范围ΔK和氢气压力\（P _ {{{\ text {H}} _ {2}}} \）。除观察断口外，还通过干涉显微镜和透射电子显微镜分析了裂纹尖端的塑性。结果，氢的FCG速率加速量随着f的减小而增加，直到达到临界值为止（f = 2 Hz，\（P _ {{{{text {H}} _ {2}}} \）= 3.5 MPa，在\（P _ {{{text {H}} _ {2}}} \） = 35 MPa时，f = 0.2 Hz ，而一旦f降至临界值以下，HAFCG速率将大大降低。同时，\（P _ {{{{text {H}} _ {2}}} \） = 3.5 MPa时的断裂模式从脆性准裂解变为更具延性的方式，没有明显的氢影响。另一方面，在\（P _ {{{\ text {H}} _ {2}}} \） = 35 MPa的情况下，类似劈开面的尺寸变大，这表明引起劈开的晶格面数量为减少，因为较少的氢效应。氢已使裂纹尖端塑性降低，而HAFCG增强在f的临界值以上时发生。。相反，在低于临界值的f时，裂纹尖端的可塑性恢复到与惰性环境几乎相同的水平。基于从裂纹尖端扩散的氢的理论估计，引起这种反向f依赖性的f的临界值很可能由裂纹尖端附近的氢浓度梯度确定。尽管仍不清楚其相关的机制，但有人认为，移动位错与氢原子扩散之间的动态相互作用对于阐明HAFCG的机制很重要。