Abstract Fatigue crack-growth (FCG) of Ni-based superalloy 718 was investigated under gaseous hydrogen environment (external hydrogen) and uniformly pre-charged state (internal hydrogen). Under external hydrogen, intergranular fracture predominated, whereas dislocation slip-band or twin boundary fracture were prevalent under internal hydrogen. This failure mode divergence encompassed unique characteristics of macroscale FCG response, leading to both cycle- and time-dependent cracking. The intergranular cracking was ascribed to short-circuit diffusion of hydrogen along grain boundaries. Meanwhile, the material’s inherently inhomogeneous deformation mode exerts harmfulness when hydrogen was uniformly distributed inside the specimen, causing slip-bands or twin boundaries to become the weakest links for fracture.

中文翻译：

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通过裂纹路径晶体学和变形微观结构揭示的镍基高温合金 718 中氢辅助疲劳裂纹扩展

摘要 研究了气态氢环境（外氢）和均匀预充状态（内氢）下Ni基718高温合金的疲劳裂纹扩展（FCG）。外氢作用下，以晶间断裂为主，而内氢作用下，以位错​​滑带或孪晶界断裂为主。这种失效模式分歧包含宏观 FCG 响应的独特特征，导致周期和时间相关的开裂。晶间开裂归因于氢沿晶界的短路扩散。同时，当氢在试样内部均匀分布时，材料固有的不均匀变形模式会产生危害，导致滑移带或孪晶边界成为断裂的最薄弱环节。