激光熔覆过程伴随着成形气氛与熔池的接触,成形气氛是影响熔覆层显微组织的重要因素。为了实现大型复杂精密、高性能金属结构件的快速制备,高沉积率激光熔覆技术在传统激光熔覆技术的基础上大幅提高能量输入与质量输入,但这也会改变熔池的形貌与温度,从而改变气氛对熔池的作用;此外,随着成形件尺寸增大,提供保护气氛的成本也将急剧增大。基于此,本文采用高沉积率激光熔覆技术分别在氩气气氛与空气气氛下进行GH4169高温合金的单道熔覆实验,研究了成形气氛对高沉积率激光熔覆GH4169合金凝固条件、熔覆层几何特征以及显微组织的影响。结果表明:不同气氛的散热条件虽然改变了熔池的凝固条件,但其对氧化作用的影响很小;与氩气气氛相比,空气气氛下熔池的冷却速率更大,熔覆层一次枝晶间距更细小,Laves相更少,微观偏析程度更低。本文研究结果说明,相比于开放的空气气氛,氩气保护气氛对高沉积率激光熔覆GH4169合金凝固条件与显微组织没有明显的增益作用,这一结果可为工业生产提供参考。

The laser metal deposition process is accompanied by the interaction of the forming environment and molten pool, which influences the solidification conditions and formed microstructure to a certain extent. To achieve the rapid production of large, complex, and high-performance metal structures, high-deposition-rate laser metal deposition (HDR-LMD, deposition rate ≥1 kg/h) technology was developed by simultaneously improving the energy and mass inputs based on the conventional laser metal deposition (C-LMD, deposition rate ≤0.3 kg/h) technology. Compared with the C-LMD process, HDR-LMD can change the shape and temperature of the molten pool, further influencing the forming environmental effect on the molten pool. Moreover, as the dimension of the forming part increases, the cost of establishing an environment chamber also increases. Based on the aforementioned background, the forming environmental effect (air and argon environments) on the solidification condition, single-layer geometry, and microstructure of HDR-LMD GH4169 superalloy was studied. Results show that although the heat dissipation of different environments influence solidification condition during the HDR-LMD process, their influences on the oxidation are very small. Moreover, compared with argon environment, air environment exhibits a greater cooling rate, finer primary dendrite arm spacing, less Laves phase content, and lower degree of microsegregation. This study indicates that the solidification condition and microstructure of HDR-LMD GH4169 alloy does not significantly improve upon being shielded with argon, which can provide a reference for industrial production.