Ni-24.19wt%Nb过共晶合金跃迁减速定向凝固下初生Ni_3Nb相的消失

Disappearance of Ni_3Nb Primary Phase in Hypereutectic Alloy of Ni-24.19wt% Nb at Abruptly Decreasing Growth Rate under Directional Solidification

对N i-24.19%Nb过共晶合金在定向凝固速率10μm/s和跃迁减速定向凝固下的组织进行了研究,结果表明:凝固速率10μm/s下,合金中出现了初生N i3Nb相的生长,并在凝固20mm后达到了准稳态,与最高界面生长温度假设的理论分析相一致。在从10μm/s跃迁减速到1μm/s过程中,界面上液相溶质的变化,造成了初生N i3Nb相的含量先增加后减少,而初生相的消失,凝固组织变为全耦合生长的共晶组织,主要是由于初生相与共晶相相互竞争生长造成的。另外,初生相的消失也不是在同一个平面上均匀进行的,而是从试样的边缘向中心逐渐发展的。

Directionally solidified microstructures of Ni-24.19wt%Nb hypereutectic alloy were investigated at the growth rate of 10μm/s,and the abruptly decreasing growth rate from 10 to 1μm/s.The results show that the microstructure consists of Ni_3Nb primary phase and eutectic(Ni+Ni_3Nb),in agreement with the theoretical calculation results at the growth rate of 10μm/s.After the solidified distance of 20mm,the growth of Ni_3Nb primary phase achieves the quasi-steady state.At the abruptly decreasing growth rate from ...