Abstract It is suspected early that the ultra-slow crack propagation in fine-granular-area (FGA) may be sensitive to the internal vacuum-like environment. In other words, fatigue failure in the very-high-cycle regime may be related to the internal vacuum-like environment. Since magnesium alloy is more susceptible to the environmental effect, it is selected as the research carrier in this study. A magnesium alloy is investigated in ambient air and vacuum environments comparatively, and the vacuum loading environment offers a valuable reference to investigate the possible environmental effect. The results show that plastic deformation mechanism in different loading environments keeps the same at crack initiation site. However, the different loading environments not only change the fatigue life, but also the failure mode. At higher stress levels, surface failure dominates in air loading environment, whereas internal failure dominates in vacuum loading environment and presents longer fatigue life. It is considered that failure mode in vacuum loading environment is mainly affected by the critical grains, whereas that in air loading environment is mainly affected by the competition between the surface air acceleration effect and the critical grains. Fatigue life is mainly affected by the internal vacuum retarding effect and the surface air accelerating effect.

中文翻译：

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真空减速和空气加速对 ZK60 镁合金高周和超高周疲劳行为的影响

摘要 人们早期怀疑细颗粒区（FGA）中的超慢裂纹扩展可能对内部真空环境敏感。换句话说，超高周疲劳失效可能与内部真空环境有关。由于镁合金更易受环境影响，本研究选择镁合金作为研究载体。镁合金在大气环境和真空环境中进行了比较研究，真空加载环境为研究可能的环境影响提供了有价值的参考。结果表明，不同加载环境下的塑性变形机制在裂纹萌生部位保持一致。然而，不同的加载环境不仅会改变疲劳寿命，还会改变失效模式。在更高的压力水平下，表面破坏在空气加载环境中占主导地位，而内部破坏在真空加载环境中占主导地位，并且具有更长的疲劳寿命。认为真空加载环境下的失效模式主要受临界晶粒的影响，而空气加载环境下的失效模式主要受表面空气加速效应与临界晶粒之间的竞争影响。疲劳寿命主要受内部真空减速作用和表面空气加速作用的影响。而在空气加载环境中，主要受表面空气加速效应与临界颗粒之间的竞争影响。疲劳寿命主要受内部真空减速作用和表面空气加速作用的影响。而在空气加载环境中，主要受表面空气加速效应与临界颗粒之间的竞争影响。疲劳寿命主要受内部真空减速作用和表面空气加速作用的影响。