Effects of P and B addition on as-cast microstructure and homogenization parameter of Inconel 718 alloy

The effects of phosphorus and boron addition on the as-cast microstructure and homogenization parameters of Inconel 718 were studied. The results indicate that the addition of phosphorus and boron promotes the formation of blocky Laves phase. Due to the strong segregation behavior of boron in the final residual liquid, a low melting B-bearing phase enriched in Nb, Mo and Cr is observed. According to the differential scanning calorimeter results and electron probe micro-analysis characterization, the solidification sequence of Inconel 718 with phosphorus and boron addition in best combination is determined as L → L+γ → L+γ+ MC → L+γ+MC+Laves → γ+MC+Laves+B-bearing phase. Accordingly, the homogenization temperature is recommended to be adjusted at least 40°C lower than that of standard Inconel 718 due to the existence of low melting B-bearing phase.