Formation of metastable phases by high-energy ball milling in the Ti-O system

Abstract

Investigation of the phase formation during mechanical alloying (MA) was systematically performed in the Ti-O system. Powder mixtures of Ti and TiO2 with various compositions and single-phase Ti2O, α-TiO and α-Ti2O3 powders were respectively subjected to planetary ball milling. According to X-ray diffractometry, high-temperature phases such as α-Ti solid solution, β-TiO and γ-Ti2O3 were observed for Ti-33 at%O (after 4 h of MA), 40–55 at%O (8 h) and 60 at%O (4 h), respectively. The metastable phase formations are discussed from various viewpoints including local pressure, local temperature, point defects, impurity and repeated deformation. The phase formations by MA are explained by primitive unit cell volume of the crystal structure as an indicator.