抽拉速率对定向凝固NiAl-43V合金组织演化的影响

Effect of withdrawal rate on microstructure evolution of directionally solidified NiAl-43V alloy

采用定向凝固技术制备Ni-28.5Al-43V过共晶合金,研究初始过渡区和稳态区在不同抽拉速率下的组织形态转变,对初生α(V)相和(α+β)共晶竞争生长进行理论计算。结果表明:在恒定温度梯度GL=310 K/cm,NiAl-43V过共晶合金初始过渡区凝固过程在低速抽拉速率下(v=(2~6)×10^-6m/s)经历胞状初生α(V)相+(α+β)共晶、枝晶α(V)相+(α+β)共晶两个阶段;中速抽拉速率(v=(10~60)×10^-6m/s)经历条状初生相、胞状初生α(V)相+(α+β)共晶、枝晶α(V)相+(α+β)共晶3个阶段;高速抽拉速率(v=(90~150)×10^-6m/s)下条状初生相阶段逐渐消失,演变为中速的后两个阶段;在抽拉速率条件下(v=(2~150)×10^-6m/s),固液界面依次经历平、胞枝、枝晶的形貌转变;初生相和共晶界面生长温度相同时,临界生长速率v1=4.31×10^-6m/s和v2=6.796 285×10^-2m/s,与生长速率v=2×10^-6m/s时的共晶组织基本吻合。

The Ni-28.5 Al-43 V hypereutectic alloy was prepared by directional solidification technique. The microstructure transition of the initial transition zone and the steady state zone at different extraction rates were studied. The primary α(V)phase and the(α+β)eutectic competition growth was theoretically calculated. The results show that at the constant temperature gradient GL=310 K/cm,the solidification process of the initial transition zone of NiAl-43 V hypereutectic alloy undergoes the cellular primary α(V)phase+(α+β)eutectic at low velocity(v=(2-6)×10^-6 m/s). Dendritic α(V)phase+(α+β)eutectic two stages,at the medium-speed drawing rate(v=(10^-60)×10^-6 m/s). The microstructure of the alloy experiences strip-like primary phase,cell-like primary α(V)phase+(α+β)eutectic and dendritic α(V)phase+(α+β)eutectic,at the high-speed drawing rate(v=(90-150)×10^-6 m/s). The strip-like primary phase gradually disappears and evolves into the latter two stages of mediumspeed,under the extraction rate of this experiment(v=(2-150)× 10^-6 m/s). The solid-liquid interface undergoes the morphological transformation of flat,cell branches and dendrites successively. By theoretically calculating the interfacial growth temperature of the primary α(V)phase and the(α+β)eutectic,the critical growth rates at the same growth temperature of the primary phase and the eutectic interface are v1=4.31×10^-6 m/s and v2=6.796 285×10^-2 m/s,respectively,which is anastomotic with that the NiAl-43 V hypereutectic alloy can obtain the complete eutectic structure at the growth rate of v=2×10^-6 m/s.