Kinetic Approach for Growth and Coalescence of Nano-Size Oxide Particles in 9Cr-ODS Steel Using High-Energy Synchrotron Radiation X-rays in SPring-8

Abstract

Nanometer size oxide particles in 9Cr-ODS steel are dispersed finely and densely in a matrix by the hot-solidification process. The size and density distribution of dispersed oxide particles is recognized as one of the main issues for ensuring good microstructural stability and high temperature strength in a high temperature (<700°C) and neutron irradiation (250 dpa) environment. However, the behavior of oxide particles in the hot-solidification process has not been determined yet. This study evaluated the correlation between nano-size oxide particles and the heat treatment temperature and time in order to characterize the mechanism of formation and the behavior during growth and coalescence of these particles in 9Cr-ODS steel raw powder. XRD and SAXS measurements were made using high-energy synchrotron radiation X-rays in SPring-8. This is the first report of the oxide complex particles (Y₂Ti₂O₇ and Y₂TiO₅) being formed from 800 to 960°C, and they were observed to grow and coalesce on increasing both heat-treatment temperature and time.