一种Ni-Fe-Cr基合金的凝固特征和偏析行为

The 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. Results show that the major precipitates are γ, γ' and MC. The phase transition route is determined as follows: L→L+γ→L+γ+MC→γ+γ'+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.