The fracture and fatigue crack growth behavior of two molybdenum alloys, containing 41 wt-% and 47.5 wt-% rhenium, respectively, are investigated. These alloys were provided in form of cold-wrought rods of 6 mm diameter and exhibit a refined microstructure with highly elongated grains and a strong fiber texture. Similarly processed pure molybdenum was used as reference material and exhibits a significantly coarser microstructure. SEN(T) and C(T) specimens were tested with R-L and L-R orientation. In both, quasi-static and fatigue crack growth experiments, L-R oriented cracks immediately kinked by 90° into the direction of grain elongation. This yields fracture toughness values and effective and long crack threshold values about twice as high as for R-L oriented cracks, which is in good agreement with calculations of a reduced local crack driving force. In both MoRe alloys a cyclic R-curve behavior was captured in fatigue crack growth tests at a load ratio of R = 0.1, while for MoRe47.5 it was still present at R = 0.7. This is attributed mainly to the coarser microstructure. The effective thresholds ∆Kth,eff of both MoRe alloys are remarkably low and deviate from a commonly used estimation, especially for the MoRe47.5 material. It is proposed that plasticity in these materials is facilitated by twinning, leading to the emission of partial dislocations from the crack tip. Although no clear microstructural or fractographic evidence was found, a recalculation of ∆Kth,eff considering partial dislocations indicates a good correlation with experimental values.

中文翻译：

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探索 MoRe 合金的断裂韧性和疲劳裂纹扩展行为


研究了两种钼合金（分别含有 41 wt-% 和 47.5 wt-% 铼）的断裂和疲劳裂纹扩展行为。这些合金以直径为 6 mm 的冷锻棒的形式提供，并表现出精细的微观结构、高度细长的晶粒和强大的纤维织构。类似加工的纯钼用作参考材料，并表现出明显较粗的微观结构。SEN（T） 和 C（T） 样品以 R-L 和 L-R 方向进行测试。在准静态和疲劳裂纹扩展实验中，LR 取向的裂纹立即向晶粒伸长方向弯曲 90°。这产生了断裂韧性值和有效和长裂纹阈值，大约是 R-L 导向裂纹的两倍，这与局部裂纹驱动力降低的计算结果非常吻合。在两种 MoRe 合金中，在载荷比 R = 0.1 的疲劳裂纹扩展试验中都捕获了循环 R 曲线行为，而对于 MoRe47.5，在 R = 0.7 时仍然存在。这主要归因于较粗的微观结构。两种 MoRe 合金的有效阈值 ∆Kth，eff 都非常低，并且偏离了常用的估计值，尤其是对于 MoRe47.5 材料。有人提出，这些材料的塑性是通过孪晶来促进的，导致从裂纹尖端发射部分位错。虽然没有发现明确的微观结构或断口学证据，但考虑到部分位错，重新计算 ∆Kth，eff 表明与实验值具有良好的相关性。