Revealing anti-oxidation mechanisms of titanium composite materials by detailed characterization of scale phase constitutions

Highlights: • The enhancement of oxidation resistance of titanium composites was related to the formation of a multi-layered oxide scale. • The decrease of oxygen partial pressure led to the formation of twinned R-TiO₂ and interfacial Ti₂AlN+Ti₂N layer. • The SiO₂ with low crystallinity was observed to fill the gaps between R-TiO₂ grains due to the excellent fluidity. • Ti(O) solid solutions would transform into R-TiO₂ at high temperature and the mechanism was elucidated by thermodynamics. To understand the oxidation mechanisms of (TiC+TiB+(TiZr)₅Si₃)/TA15 composites and elucidate their superior oxidation resistance, a systematically microstructural characterization of the oxide scale was investigated. The results showed that the oxide scale was consisted of the outer R-TiO₂+Al₂O₃ mixed layer, inner gradient R-TiO₂ layer, dispersive amorphous/nanocrystalline SiO₂ and interfacial Ti₂AlN+Ti₂N layer. Such multi-layered structure could efficiently hinder the penetration of oxygen and alleviate the thermal stress generated during cyclic oxidation. Moreover, the thermodynamic stabilities of different Ti-O compounds were calculated by the first principles method, which revealed the evolution of Ti-O compounds.