Effect of alloying elements on the stability of Ni 2M in Alloy690 based upon thermodynamic calculation

摘要

Some researchers recently point out that Ni based alloys used in nuclear power plants have the ordering tendency, which is a potential to decrease mechanical properties within the expected lifetime of the plants. In the present study, authors evaluated the effect of 8 alloying elements on the ordering tendency in Alloy690 based upon thermodynamic calculation by Thermo-Calc. It is clarified that the additive amount of Fe, Cr, Ti and Si, particularly Fe and Cr, was influential for the stability of Ni 2M, while that of Mn, Cu, B and C had almost no effect for that. Authors therefore designed the Ni 2M stabilized alloy by no addition of Fe in Alloy690. Ni 2M is estimated to be stable even at 773 K in the Ni 2M stabilized alloy. The influence by long range ordering or precipitating of Ni 2M in Alloy690 for mechanical properties or SCC susceptibility is expected to be clarified by the sample obtained in the present study.