Enhancement of Fatigue Damage due to Environmental Variation and its Recovery Treatment

钢的疲劳性能受环境条件的强烈影响，其中氢起着至关重要的作用。阐明降低易感性的机制和措施一直是许多研究的主题。我们提出了一个新的模型，要求加强形成的空位在塑性变形过程中的帮助下，氢和空位的凝固，导致韧性裂纹扩展阻力的下降钢的氢脆。在此基础上，着重研究了环境条件变化对氢致疲劳敏感性的影响。首先，在疲劳过程中产生的缺陷已被发现使用氢作为探针，揭示了空位的形成作为疲劳损伤的一个因素。疲劳损伤和氢之间的相互作用导致疲劳性能的劣化和对氢相关失效的敏感性增强。在同一 ...更多信息 在此基础上，在高强度钢的延迟断裂试验中，证实了外加应力和充氢电流密度的循环变化及其协同效应会提高敏感性。预疲劳试样在低至200℃的温度下退火，恢复了磁化率的提高。生物医学材料（一种用于口腔的形状记忆镍钛合金）中与氢相关的失效的演变已被揭示。所提出的模型已被直接证明与透射电子显微镜使用标本制造的聚焦离子束方法从下面的断裂表面。与局部非晶化相关的裂纹扩展已经被揭示，支持空位密度的增加。氢微印技术也被应用于揭示捕获氢的缺陷的局部分布。电子衍射动态观察已成功地应用于揭示纳米尺度的样品表面结构。少

Fatigue properties of steel are strongly affected by environmental conditions, in which hydrogen plays an essential role. The clarification of the mechanism and measures for reducing the susceptibility have been subjects of many studies. We have proposed a new model for hydrogen embrittlement of steel that claims enhanced formation of vacancies during plastic deformation with the aid of hydrogen and the coagulation of vacancies that leads to the decrease in the ductile crack growth resistance. Based on the model, the aim of the present studies is to investigate particularly die effect of variations of environmental conditions on the susceptibility to hydrogen-related feilure. Firstly, defects created during fatigue have been detected using hydrogen as a probe, revealing the formation of vacancies as a fector of fetigue damage. Interactions between fatigue damage and hydrogen result in degradation of fatigue properties and enhanced susceptibility to hydrogen-related failure. On the same … More basis, in a delayed fracture test of a high strength steel cyclic variations of the applied stress and hydrogen-charging current density and their synergetic effect have been confirmed to enhance the susceptibility. Annealing of pre-fatigued specimens at temperatures as low as 200℃ recovered the enhancement of the susceptibility. Evolution of hydrogen-related failure in a biomedical material, a shape-memory NiTi alloy that is uses in oral cavity, has been revealed. The proposed model has been directly proved with transmission electron microscopy using specimens fabricated by means of a focused ion beam method from just beneath fracture surface. Crack growth associated with local amorphization has been revealed, supporting the increased density of vacancies. Hydrogen microprint technique has been also applied for revealing local distribution of defects that trap hydrogen. Dynamic observation of electron diffraction has been successfully applied for revealing the surface structure of specimens in nanometer-scale. Less