Microstructure and oxidation of hot-dip aluminized titanium at high temperature

High-temperature diffusion of a hot-dip aluminized titanium is conducted to study microstructure changes and oxidation behavior of the aluminized titanium. After aluminizing, the titanium substrate is covered by a black layer in which tiny block-shaped TiAl₃ particles are scattered in aluminum matrix. Based on the diffusion experiment results, the thickness of the aluminum diffusion layer at 800 °C increases with diffusion time. However, the aluminum diffusion layer at 900 °C grows and reaches its maximum thickness in 6 h, and then the thickness of the aluminum diffusion layer is reduced with prolonged diffusion time. An inversion of the diffusion layer thickness versus time appears for the aluminized titanium treated at 1000 °C, and the thickness of the diffusion layer keeps declining with diffusion time. The phases present in the outer and middle sublayers are titanium-rich TiAl₃ and equilibrium TiAl₃, respectively. However, the phase in inner sublayer changes from titanium-rich TiAl₃ to TiAl₂ and TiAl as diffusion temperature and time increase. Through energy-dispersive X-ray and X-ray diffraction analysis, the oxides formed in the oxidation process are Al₂O₃ and Al₂TiO₅. Although the oxide scale formed on the surface of the aluminized titanium has an insufficient stability and integrity, the thermal oxidation resistance of the aluminized titanium is still improved by over 5 times compared with that of the pure titanium.