Effect of Y2Ti2O7 on microstructure and tensile properties of ODS-CLAM steel

Abstract

Nano-Y2Ti2O7 is one of the phases used for improving the strength of oxide dispersion strengthened (ODS) steels, which is usually precipitated with Ti and Y2O3 added. The effect of synthesized Y2Ti2O7 on China low activation martensitic (CLAM) steel was studied. Two kinds of ODS-CLAM samples with nano-Y2Ti2O7 and amorphous Y2Ti2O7 additions were prepared using mechanical alloying (MA) and spark plasma sintering (SPS). The results indicates that amorphous Y2Ti2O7 powders had both amorphous and crystal oxides after milling with CLAM powders. Y2Ti2O7 powders were refined to below 10 nm in size with almost no structural change, and randomly distributed in the matrix. The initial size of added Y2Ti2O7 had a smaller impact on the size of precipitates, and the initial structure or the transform of the oxides during milling process were more important. The added Y2Ti2O7 particles were refined from ∼32 nm to 9.2 nm in size, while the size of amorphous Y2Ti2O7 particles was reduced from micron size to 6.9 nm in the sintered sample. The structure of Y2Ti2O7 in ODS powders affected the microstructure and strength of the sample after sintering. The sample with Y2Ti2O7 had higher strength and lower plasticity at both room temperature and 650 °C because of the higher dislocation density, while the sample with amorphous Y2Ti2O7 had higher plasticity with almost the same yield strength due to its higher dispersion strengthening. This study reveals the changes in Y2Ti2O7 structure during preparation process and suggests that the expected properties of ODS steels can be obtained by controlling the oxide structure.