Oxidation Behavior of Al2O3 Coating on Ti-25Al-12.5Nb Alloy

Abstract

The oxidation behavior of Al 2 O 3 coating deposited on Ti-25Al-12.5Nb alloy by sol-gel method was investigated at 700 and 800°C under isothermal oxidation conditions in air. At both temperatures, the coated samples exhibited reduced mass gain compared to uncoated alloy; at 700°C rather insignificant differences were observed; however, at the temperature of 800°C, the deposited coating strongly limits the mass gain of the test material. As a consequence of the isothermal oxidation a scale forms containing mainly TiO 2 on the alloy surface of the uncoated alloy, while during the oxidation of the coated alloy the surface coating of Al 2 O 3 dissociated and the initially compact Al 2 O 3 coating dissolved and its place was taken by a porous scale. These coated samples displayed good resistance to oxidation in set conditions and no zones of dissolved oxygen and nitrogen were recorded. No spallation of the coated samples was observed.

A Short Review on the Phase Structures, Oxidation Kinetics, and Mechanical Properties of Complex Ti-Al Alloys

“…However, TiO 2 is more stable and tends to grow faster than Al 2 O 3 due to the strong disorder present in its crystal lattice. The thermodynamic stability of Al 2 O 3 can be increased by increasing Al content, which also intensifies the activity of Al [15]. Al 2 O 3 is more stable with an Al content greater than 50 at.%, whereas below this concentration, the thermodynamic stability of TiO 2 is higher [16].…”