一种Ni-Fe-Cr基合金的凝固特征和偏析行为研究

Solidification Characteristics and Segregation Behavior of a Ni-Fe-Cr based Alloy

摘要:

采用定向凝固技术结合液淬法研究了一种Ni-Fe-Cr基合金平界面和枝晶生长条件下的凝固特征和溶质偏析行为。结果表明，合金的组成相为γ基体、MC型碳化物和γˊ沉淀强化相，凝固顺序为L→L+γ→L+γ+MC→γ+γˊ+MC。平界面生长条件下淬火界面两侧溶质含量测定结果表明， Ti、Nb和Mo元素富集于液相，溶质分配系数小于1。Fe元素富集于固相，溶质分配系数大于1。Al和Cr元素在液固两相中浓度差别较小，溶质分配系数接近1。此外，固/液界面前沿存在溶质边界层，边界层内溶质原子通过扩散传输，边界层外主要借助流动传输。枝晶与平界面生长的溶质偏析行为基本一致，然而，枝晶生长时糊状区残余液相中溶质浓度与平界面生长时固/液界面前沿溶质浓度存在显著差别。枝晶生长条件下糊状区溶质偏析程度显著高于稳态生长区，固相反扩散和MC型碳化物的析出显著降低枝晶偏析程度。

Abstract:

Solidification characteristics and segregation behavior of a Ni-Fe-Cr based alloy with planar interface and dendritic growth, which was obtained through quenching experiments during directional solidification, were investigated in this paper. The major precipitates are γ, γ′ and MC. The phase transition route is determined as follows: L→L+γ→L+γ+MC→γ+γˊ+MC. The solution distribution coefficients of Ti, Nb and Mo are less than unity. The solution distribution coefficients of Fe is greater than unity and, Al and Cr are close to 1. The solute boundary layer forms ahead of the liquid/solid interface when the steady-state growth begins. The solute is carried away mainly by diffusion in the solute boundary layer, but carried away mainly by flow out of the solute boundary layer. The solute distribution in solid phase with dendritic growth is similar to that with planar interface growth. However, the solute concentration in the quenched liquid in the interdendritic area is obviously higher than that ahead of the liquid/solid interface. The solidification segregation of the mushy zone is more serious than that of the solid region. It indicates that the back-diffusion in solid phase and the precipitation of MC carbide would reduce the solidification segregation during the dendritic growth.