Abstract A multi-track single crystal structure produced by laser cladding can be succeeded on a flat but failed on complex geometry for single crystal superalloys repair. It was always accompanied with stray grains and cracks when the complex shape defects were repaired by laser cladding. According to analysis, the geometrical profile of the defect may change the heat dissipation condition during laser cladding so that it promotes to form stray grains locally. In this paper, the off-axis heat flow angle (β) which was defined by the heat flow direction and the dendritic growth direction, was used to evaluate the formation of stray grains. Results showed that dendrites grew epitaxially along the preferred crystal orientation which was closer to heat flow. In addition, stray grains could not be formed in the epitaxial columnar dendrite region until the β was more than the critical value of 30°. Two preferred orientations competed for growth perpendicular to each other when the β was close to 45°. Therefore, the repair principle was proposed that the β was not more than 30° ensured by geometrical profile design, and a v-groove defect was successfully guided and repaired.

中文翻译：

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单晶镍基高温合金的外延激光沉积：复杂几何形状的修复

摘要 激光熔覆产生的多道单晶结构可以在平面上成功，但在复杂几何形状的单晶高温合金修复中失败。激光熔覆修复形状复杂的缺陷时，往往伴随着杂散晶粒和裂纹。据分析，缺陷的几何轮廓可能会改变激光熔覆过程中的散热条件，从而促进局部杂散晶粒的形成。在本文中，由热流方向和枝晶生长方向定义的离轴热流角 (β) 用于评估杂散晶粒的形成。结果表明，枝晶沿更接近热流的优选晶体取向外延生长。此外，直到β大于30°的临界值，才能在外延柱状枝晶区形成杂散晶粒。当 β 接近 45°时，两个优选取向相互竞争生长。因此，提出通过几何轮廓设计保证β不大于30°的修复原则，成功引导修复一个V型槽缺陷。