Effect of phosphorus segregation on as-cast microstructure and homogenization treatment of IN706 alloy

The distribution of phosphorus in IN706 alloy was studied, with particular emphasis on the as-cast microstructure and homogenization treatment. It is found that phosphorus is segregated in Laves phase and markedly influences the as-cast microstructure of IN706 alloy. Phosphorus retards the formation of Laves phase with the eutectic form, but promotes the Laves formation with the blocky form. Phosphorus refines the dendritic structure and noticeably enlarges the interdendritic area. The reason for phosphorus influencing the as-cast microstructure is attributed to its extremely low solubility in γ matrix and great retarding effect on γ matrix solidification. In addition, phosphorus slightly decreases the melting temperature of Laves phase, and retards the dissolution of Laves phase and the element diffusion between dendrite core and interdendritic area during the homogenization treatment. And it is thought that phosphorus delays the homogenization process by inhibiting the element diffusion.