Abstract A paraxial powder-feeding system by employing a quasi-continuous fiber laser machine was established to repair non-weldable nickel-based K447A alloy. In the present study, the duty cycle (DC) of the pulsed-wave laser was chosen to reveal the influence on hot cracking. The results showed that the total length of hot cracking on the 10.5 mm-length longitudinal section of the cladding zone reduces from 3.263 mm to 0.092 mm with the decline of DC from 80% to 30%. The intermittent occurrence of the laser beam induced the ripple microstructure in the cladding layer (CL). It is the high cooling rate in laser extinguishment process that caused the fine dendrite zone which provides more resistance for hot cracking propagation in the CL. The liquid film in the heat-affected zone (HAZ) mainly results from the M5B3/γ, γ′/γ, and MC/γ constitutional liquation successively among 1200–1300 °C. Heat input is the main factor affecting hot cracking in the HAZ. With the decrease of DC, the dendrite spacing of the fine dendrite zone decreases in the CL, and the depth of liquefaction zone decreases in the HAZ, as a result, the length of hot cracking in the CL and HAZ both decreases.

中文翻译：

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脉冲波激光特性对抑制激光熔覆不可焊镍基高温合金热裂纹的作用

摘要 采用准连续光纤激光机建立了近轴送粉系统，用于修复不可焊镍基K447A合金。在本研究中，选择脉冲波激光器的占空比 (DC) 来揭示对热裂纹的影响。结果表明，随着DC从80%下降到30%，熔覆区10.5 mm纵截面上的热裂纹总长度从3.263 mm减小到0.092 mm。激光束的间歇性出现在熔覆层（CL）中引起波纹微结构。正是激光熄灭过程中的高冷却速度导致了细小的枝晶区，从而为 CL 中的热裂纹扩展提供了更大的阻力。热影响区（HAZ）中的液膜主要由 M5B3/γ、γ′/γ、和 MC/γ 在 1200-1300 °C 之间相继发生结构液化。热输入是影响热影响区热裂的主要因素。随着 DC 的减小，CL 中细枝晶区的枝晶间距减小，HAZ 中液化区的深度减小，因此 CL 和 HAZ 中的热裂纹长度均减小。