凝固参数对DD6偏析和g/g ′共晶组织演化的影响

Effect of Solidi?cation Parameters on the Segregation and g/g ′ Eutectic Evolution in Ni-Based Single Crystal Superalloy DD6

摘要:

采用液态金属冷却高梯度定向凝固技术，在2~400 μm/s的抽拉速率范围内对镍基单晶高温合金DD6的凝固组织、偏析和g/g ′共晶组织演化进行了研究。采用电子探针微区分析（EPMA）定量分析了溶质元素的微观偏析行为，讨论了溶质元素偏析及枝晶间距对共晶组织演化的影响。结果表明：随着抽拉速率增大，共晶体积分数先增多后减少。在较低的冷却速率下，固相反扩散能够减轻微观偏析，从而减少共晶体积分数，而在高的冷却速率下，固相反扩散的作用被严重削弱，枝晶间距减小对减少共晶体积分数起到了十分重要的作用

Abstract:

The microstructure, the segregation and the evolution of g/g ′ eutectic during the solidi?cation of Ni-base superalloy DD6 prepared by dual heating zone melting and liquid-metal cooling (LMC) direction solidification technique were investigated over a range of cooling rates. The microsegregation behavior during solidi?cation was also quantitatively examined by EPMA to clarify the in?uence of elemental segregation on the evolution of g/g ′ eutectic. The effect of dendrite arm spacing was also taken into consideration. The results demonstrate that the g/g ′ eutectic fraction first increases and then decreases with the increasing of cooling rate. The back-diffusion in solid phase would reduce the microsegregation during dendrite growth. Back-diffusion occurs during the solidi?cation of Ni-based single crystal superalloy DD6, but its influence on decreasing of the volume fraction of g/g ′ eutectic would be negligible depending on the diffusivity of each solute element when the cooling rate is up to a certain limit. As the cooling rate increases, the dilution effect of microsegregation owing to dendrite arm spacing decrease plays a leading role during solidi?cation