Slip transfer/blocking at grain and twin boundaries as well as preferential fatigue crack nucleation locations were studied in two solution-hardened Ni-based alloys (Inconel 600 and Hastelloy C276) deformed under strain-controlled, fully-reversed cyclic deformation in the low-cycle fatigue regime. Electron backscatter diffraction-based slip trace analysis was used to identify the active slip systems after interrupted fatigue tests. It was found that the Luster-Morris parameter m′=0.6 was an accurate geometrical criteria to discriminate between slip transfer and blocking at grain and twin boundaries. Moreover, it was found that fatigue cracks initiation was always intergranular and cracks were nucleated at grain and twin boundaries when the slip transfer across was blocked. The probability of crack nucleation increased with the misorientation angle and was independent of the grain size. This behavior was associated with the development of stress concentrations at grain and twin boundaries as well as triple junctions in which slip was blocked and is different from previous reports on fatigue crack nucleation in Ni-based superalloys deformed, in which the slip system parallel to the TB in the parent grain was suitably oriented for slip. This contrast in the fatigue crack nucleation sites between both types of Ni alloys were attributed to the differences in the degree of strain localization and show how this factor controls damage nucleation in polycrystals.

中文翻译：

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固溶硬化镍基合金应变控制疲劳过程中晶粒和孪晶界的滑移转移和裂纹萌生


研究了两种固溶硬化镍基合金（Inconel 600 和 Hastelloy C276）在低周疲劳状态下在应变控制、完全反向循环变形下变形的晶粒和孪晶界的滑移转移/阻塞以及优先疲劳裂纹成核位置。采用基于电子背散射衍射的滑移轨迹分析来识别间断疲劳试验后的主动滑移系统。研究发现，Luster-Morris 参数 m′=0.6 是一个准确的几何标准，用于区分晶粒和孪晶界的滑移转移和阻塞。此外，还发现疲劳裂纹的起始总是晶间的，当滑移传递受阻时，裂纹在晶粒和孪晶界处成核。裂纹成核的概率随着取向差角的增加而增加，并且与晶粒尺寸无关。这种行为与晶粒和孪晶界以及滑移被阻塞的三重结处应力集中的发展有关，这与以前关于镍基高温合金变形疲劳裂纹成核的报道不同，其中平行于母晶中 TB 的滑移系统适合滑移。两种 Ni 合金之间疲劳裂纹成核位点的这种对比归因于应变局部化程度的差异，并显示了该因素如何控制多晶中的损伤成核。