Dendrite Deformation in the Rejoined Platforms of Ni-Based Single-Crystal Superalloys

Dendrite deformation often occurs during the preparation of single-crystal superalloy blades by directional solidification and can cause solidification defects, such as low-angle boundaries (LABs), slivers, and orientation deviations. Continuous dendritic deformation is uncommon and its mechanisms and influencing factors are poorly understood. However, this can lead to significant orientation deviation and performance degradation. Herein, a model with rejoined platforms is designed to study the dendrite growth and orientation evolution in a rejoined platform of Ni-based single-crystal superalloys. It is indicated in the results that, under certain conditions, the developed secondary dendrites deform continuously near the mold wall of the rejoined platforms and the resulting disorientation has a cumulative effect. Finally, LABs and dendritic fragments appear on the rejoined platforms. Thus, the integrity of the single crystal is destroyed. This can be the result of the local shrinkage stress on the long secondary dendrites within a sufficient growth space.     

单晶镍基合金在拉伸蠕变期间的组织演化与分析

通过[001]取向镍基单晶合金拉伸蠕变期间的组织形貌观察,采用应力应变有限元方法计算出立方γ/γ′两相共格界面的vonMises应力分布,研究了合金在蠕变期间γ′相的定向粗化规律。结果表明,施加拉应力可改变立方γ/γ′两相的应力分布,使不同晶面发生晶格收缩与扩张应变,其中,(001)晶面产生晶格收缩可排斥较大半径的Al、Ti原子,(100)和(010)晶面沿平行于应力轴方向产生晶格扩张应变,可诱捕较大半径的Al、Ti原子,是使其γ′相沿扩张晶格的法线定向生长成为类似筛网层状结构的组织演化规律。并进一步提出蠕变期间发生元素扩散和γ′相定向生长的驱动力。