Abstract:

The effect of phosphorus content and heat treatment on the segregation of phosphorus and precipitation of phosphide at the grain boundary of IN706 alloy has been investigated. The phosphide had a stoichiometry of MNP (M?=?Nb, Ti and N? =?Ni, Fe, Cr) and an orthorhombic crystal structure. The solubility of phosphorus in the grain matrix of IN706 alloy was determined to be between 0.008% and 0.013%. When soaked at 980?°C for 5?min, the phosphide was noticeably precipitated at grain boundaries with the grain size unchanged. When soaked at 980?°C for 3?h, the grains grew significantly, but the phosphide stayed at original grain boundaries which outlined the grain shape before soaking. Soaking at 1060?°C for 2?h fully dissolved the pre-existing phosphide but phosphorus atoms were not distributed uniformly in the grain matrix. When the holding time at 1060?°C was extended to 10?h, the phosphorus atoms were distributed uniformly in the grain matrix by sufficient diffusion, and the phosphide could only be formed at grain boundaries during the 980?°C soaking. The precipitation of phosphide mainly relied on the phosphorus segregation which was built up by diffusion.

Key words: Phosphorus, Phosphide, IN706 alloy, Grain boundary segregation