Stably controlling the monocrystalline nature in the repaired zone is a longstanding challenge for the laser additively repair of single-crystal components. In this study, the coupling effect of laser defocusing amount and scanning speed on the molten pool morphology and associated crystal growth behaviors in laser powder deposition of single-crystal superalloy was studied through single-track experiments and an improved mathematical model. Multi-layer experiments were conducted to verify the practicability of optimized processing parameters. The results indicated that the defocusing amount can effectively adjust the laser energy intensity distribution through changing the laser-powder interaction distance and resultantly tailor the molten pool morphology and associated crystal growth behaviors. With the defocusing amount changing from − 3 to + 3 mm, the toe angle of molten pool increases dramatically and induces the formation of nonideal columnar crystals at the toe edge. The increase in laser scanning speed shrinks the molten pool size, restrains the formation of stray grains and nonideal columnar crystals, and enhances the total-remelting ability of stray grains. Coupling tailoring negative defocusing amount and proper scanning speed (− 3 mm and 9 mm/s are optimal under the given conditions) benefits the epitaxial-growth continuity of columnar dendrites and reproduces complete monocrystalline structure in laser SX-repair process.

稳定控制修复区的单晶性质是激光增材修复单晶部件的长期挑战。本研究通过单道实验和改进的数学模型，研究了激光散焦量和扫描速度对单晶高温合金激光粉末沉积中熔池形貌及相关晶体生长行为的耦合影响。通过多层实验验证优化工艺参数的实用性。结果表明，离焦量可以通过改变激光与粉末的相互作用距离来有效调节激光能量强度分布，从而调整熔池形貌和相关的晶体生长行为。随着散焦量从-3 变为+ 3 mm，熔池趾角急剧增加，并在趾缘形成非理想柱状晶。激光扫描速度的提高缩小了熔池尺寸，抑制了杂晶和非理想柱状晶的形成，增强了杂晶的全重熔能力。调整负离焦量和适当的扫描速度（在给定条件下最佳为 - 3 mm 和 9 mm/s）的耦合有利于柱状枝晶的外延生长连续性，并在激光 SX 修复过程中再现完整的单晶结构。抑制杂晶和非理想柱状晶的形成，增强杂晶的全重熔能力。调整负离焦量和适当的扫描速度（在给定条件下最佳为 - 3 mm 和 9 mm/s）的耦合有利于柱状枝晶的外延生长连续性，并在激光 SX 修复过程中再现完整的单晶结构。抑制杂晶和非理想柱状晶的形成，增强杂晶的全重熔能力。调整负离焦量和适当的扫描速度（在给定条件下最佳为 - 3 mm 和 9 mm/s）的耦合有利于柱状枝晶的外延生长连续性，并在激光 SX 修复过程中再现完整的单晶结构。