激光增材制造高Nb含量GH4169合金微观偏析行为研究

Dendritic Segregation of Nb Modified GH4169 Superalloy Fabricated by Laser Additive Manufacturing

目的减轻不同热处理状态下激光增材制造高Nb含量GH4169合金组织中的微观偏析。方法采用激光增材制造方法对球磨Nb合金化后的合金粉末进行快速成形,获得具有较高Nb含量的GH4169合金试样。通过光学显微镜、扫描电子显微镜及能谱分析、维氏硬度测试方法,对沉积态、固溶态和直接时效态试样进行分析,研究因合金中Nb含量变化引起的微观偏析对沉积态和热处理态合金的枝晶组织和显微硬度的影响。结果随着Nb含量的增加,一方面,由于枝晶间的Nb含量增加,枝晶间(γ+Laves)共晶数量增加,且共晶组织形貌更为连续;沉积态试样的显微硬度由228.4HV增大至534.1HV。另一方面,枝晶干Nb元素含量增加,枝晶干与枝晶间Nb元素含量的差异缩小,Nb元素的偏析比由8.59减小至4.13。后续固溶处理后,枝晶结构逐渐消失,枝晶间Laves相的数量随之减少,枝晶干与枝晶间的微观偏析减轻;固溶态试样硬度值随之减小,减小趋势随固溶温度的升高而逐渐平缓。随着Nb含量的增加,直接时效处理后,各试样显微硬度值在微观区域内的均匀性提高,枝晶干与枝晶间强化相的析出差异减小。结论合适的热处理制度既可以实现合金元素的均匀化,还能减小枝晶干与枝晶间强化相的析出差异,减轻激光增材制造高Nb含量GH4169合金组织中的微观偏析。

The work aims to alleviate dendritic segregation of Nb modified GH4169 superalloy fabricated by laser additive manufacturing(LAM) after different heat treatments. Nb powders were added to the original GH4169 superalloy powder by ball milling, and the alloying GH4169 samples with high Nb content were fabricated by LAM. The as-deposited, solid solution and direct aging(DA) samples were analyzed by optical microscopy(OM), scanning electron microscopy(SEM), energy spectrum analysis(EDS) and Vickers hardness test. The effects of dendritic segregation caused by Nb content in LAM alloying GH4169 superalloy on microstructure and microhardness of as-deposited and heat treated sample were studied. On the one hand, the addition of Nb made the dendrite structure more obvious, and promoted the precipitation of γ+Laves interdendritic eutectics, and the morphology of γ+Laves interdendritic eutectics was gradually like net. With the increase of Nb content in LAM alloying GH4169 superalloy, the hardness value could reach 534.1 HV from 228.4 HV. On the other hand, the content of Nb in the dendrite core increased and the differences between dendrite core and interdendrite decreased, which made the segregation ratio decreased from 8.59 to 4.13. After solution treatment, the dendrite structure characteristics of the sample disappeared obviously with the rise of heat treatment temperature. The quantity of Laves phase between dendrites decreased and the microhardness value decreased because of the different degree dissolution of the Laves phase, showing the alleviation of dendritic segregation of LAM alloying GH4169 superalloy. The decreasing trend gradually dwindled with the increase of solution temperature. With the increase of Nb content, the microhardness uniformity of samples after aging treatment was improved and the difference of precipitation of strengthening phases in dendritic structure reduced. Suitable heat treatment can not only make alloying elements homogenized, but also reduce the difference of precipitation of strengthening phases in dendritic structure, and alleviate the dendritic segregation in LAM alloying GH4169 superalloy.