A successful near-net-shape tip-remanufacturing process of single-crystal (SX) turbine blades should sustain a monocrystalline nature in the restored zone. Laser additive manufacturing (LAM) technique shows the huge potential to faultlessly restore the damaged tip of SX turbine blades. In this study, the microstructure formation in the near-net-shape tip-remanufacturing process of SX superalloy is studied through LAM experiments and simulation. The results indicate that due to the asymmetric heat diffusion condition at the top surface edge of SX substrate, the increase of laser power destroys the symmetry of morphologic size and microstructure formation in the single-track bead with a rapidly increased melting depth at the left side. Disoriented grains at the right side of the sing-track bead multiply layer by layer, gradually irrupting the epitaxial-growth continuity of columnar dendrites and resultantly destroying the monocrystalline nature of remanufactured tip structure. The continuous forced cooling of substrate not only shrinks the bead morphologic size, but also inhibits the disoriented grains formation at the right side of the single-track bead by directionally enhancing the epitaxial-growth ability of columnar dendrites. With the optimized laser power 550 W and continuously cooling substrate to −20 °C, a near-net-shape remanufactured tip structure with completely SX microstructure is achieved. The results provide an effective method to control the microstructure formation in the laser additive tip-remanufacturing application of SX turbine blades via coupling adjusting the laser power and continuous substrate forced cooling.

成功的单晶（SX）涡轮叶片近净形尖端再制造工艺应在恢复区保持单晶性质。激光增材制造（LAM）技术显示出巨大的潜力，可以完美地修复SX涡轮叶片的受损尖端。本研究通过LAM实验和模拟研究了SX高温合金近净形尖端再制造过程中的显微组织形成。结果表明，由于SX衬底顶表面边缘处的热扩散条件不对称，激光功率的增加破坏了单轨磁珠的形态尺寸和微观结构形成的对称性，并且左侧的熔化深度迅速增加。 。歌唱道珠子右侧的乱七八糟的晶粒逐层增加，逐渐破坏了柱状树枝状晶体的外延生长连续性，并因此破坏了再制造尖端结构的单晶性质。基板的连续强制冷却不仅缩小珠粒的形态尺寸，而且还通过定向增强柱状枝晶的外延生长能力，抑制了单轨珠粒右侧散乱的晶粒形成。通过优化的550 W激光功率和将基板连续冷却至-20°C，可获得具有完全SX微观结构的近净形再制造尖端结构。该结果提供了一种有效的方法，通过耦合调整激光功率和连续的基板强制冷却来控制SX涡轮叶片的激光添加剂尖端再制造应用中的微结构形成。