The present work contributes to a better understanding of the effect of stress multiaxiality on the creep behavior of single crystal Ni-base superalloys. For this purpose we studied the creep deformation and rupture behavior of double notched miniature creep tensile specimens loaded in three crystallographic directions [100], [110] and [111] (creep conditions: 950 °C and 400 MPa net section stress). Crystal plasticity finite element method (CPFEM) was used to analyze the creep stress and strain distributions during creep. Double notched specimens have the advantage that when one notch fails, the other is still intact and allows to study a material state which is close to rupture. No notch root cracking was observed, while microstructural damage (pores and micro cracks) were frequently observed in the center of the notch root region. This is in agreement with the FEM results (high axial stress and high hydrostatic stress in the center of the notched specimen). Twinning was observed in the notch regions of [110] and [111] specimens, and <112> {111} twins were detected and analyzed using orientation imaging scanning electron microscopy. The present work shows that high lattice rotations can be detected in SXs after creep fracture, but they are associated with the high strains accumulated in the final rupture event.

本工作有助于更好地理解应力多轴性对单晶镍基高温合金蠕变行为的影响。为此，我们研究了在三个晶体学方向[100]，[110]和[111]（蠕变条件：950°C和400 MPa净截面应力）下加载的双缺口微型蠕变拉伸试样的蠕变变形和断裂行为。晶体塑性有限元方法（CPFEM）用于分析蠕变过程中的蠕变应力和应变分布。双缺口样品的优势在于，当一个缺口失效时，另一个缺口仍完好无损，并可以研究接近破裂的材料状态。没有观察到切口根部开裂，而在切口根部区域的中心经常观察到微结构损伤（孔和微裂纹）。这与有限元分析结果一致（缺口样品中心的高轴向应力和高静水应力）。在[110]和[111]标本的缺口区域中观察到孪晶，并使用取向成像扫描电子显微镜检测并分析了<112> {111}孪晶。目前的工作表明蠕变断裂后可以在SX中检测到高晶格旋转，但它们与最终断裂事件中积累的高应变有关。