Study on the formation mechanism of Y-Ti-O oxides during mechanical milling and annealing treatment

摘要

Y-Ti-O nano-scale oxides play important roles in ensuring the excellent performance of oxide dispersion strengthened (ODS) steels. In this study, a model powder system of Y2O3 and Ti was designed to investigate the formation and evolution mechanism of Y-Ti-O oxides. The morphology of powders tended to be stable after high energy ball milling for 240 min in Ar. X-ray diffraction (XRD) results suggested that there was no formation of new phase after mechanical milling. Thermo-gravimetric and differential thermal analysis (TG-DTA) was applied to analyze physical and chemical reactions of milled powders respectively in Ar and air. The corresponding annealing and XRD were performed to study the types and structures of oxides at different temperatures. It shows that oxygen concentration and temperature are the critical factors affecting the formation of oxides. Ti was evolved into Ti6O, Ti3O and TiO2 in turn with temperature increasing. Then only TiO2 was reacted with Y2O3 to form Y2Ti2O7. The formation of Y2Ti2O7 began at around 500 celcius and was completed around 1004 celcius. A maximum formation rate occurred at about 779 celcius. High resolution transmission electron microscopy (HRTEM) suggested that the main phase in powders sintered at 1100 celcius was identified as pyrochlore structure Y2Ti2O7.