Fatigue Characterization of Ultrahigh Strength and Ductile Mg-Gd-Y-Zn-Zr Alloy with Hierarchical Anisotropic Nanostructure

研究了具有长周期堆垛有序相（LPSO）的镁合金的超高周疲劳行为。疲劳断裂和损伤观察表明，微裂纹从较厚的α-Mg层形核，远离致密的LPSO层。值得注意的是，微裂纹成核内观察到本地化的氧化物。这项调查突出了高度本地化的氧化物增厚，数量级厚于原生氧化物，在微裂纹成核的过程中的关键作用。所提出的模型重申了挤压/侵入过程的重要性，但更重要的是突出了一种机制，其中疲劳诱导的氧化导致挤压/侵入结构的脆化，这反过来又影响微裂纹的成核。

We investigated the very high cycle fatigue behavior of a Mg alloy with long-period stacking ordered (LPSO) phase. Fatigue fracture and damage observation revealed that microcracks nucleate from the thick alpha-Mg layers, away from the dense LPSO lamellae. Notably, microcrack nucleation was observed inside the localized oxides. This investigation highlights the critical role of highly localized oxide thickening, orders of magnitude thicker than native oxide, in the process of microcrack nucleation. The proposed model reaffirms the importance of the extrusion/intrusion process, but more importantly highlights a mechanism in which fatigue-induced oxidation results in the embrittlement of the extrusion/intrusion structure, which in turn affects the nucleation of microcracks.