Precipitation behavior of second phases during isothermal oxidation of Hastelloy C-2000 alloys

The precipitation behavior of the second phase in Hastelloy C-2000 alloy matrix was studied after isothermal oxidation at 800℃ for 100 h in air. Mo-rich phase was precipitated in the alloy matrix after oxidation. According to the determination Mo-rich phase with diamond cubic structure is Mo₃Ni₃C type carbide. Morphology characteristics of Mo-rich phase with both no-continuous and continuous irregular strip are presented along grain boundaries and in matrix, respectively. However, some variation of morphologies will take place at both grains and grain boundaries after deep etching, i.e. a large number of white flocculent structure are distributed along grain boundaries, and the corrosion pits with a diamond structure appear in intragranular. Ni-rich and Cr-rich areas are more easily corroded during deep etching due to a more negative electrode potential in the areas.