High temperature oxidation behaviors of Al/Cr composite coating on Ti2AlNb alloy

Abstract

The Al/Cr coatings were deposited on Ti2AlNb alloy by magnetron sputtering and double glow plasma alloying technology to improve the oxidation resistance. The morphology of the protective coating was investigated by scanning electron microcopy and the phase composition of the coating was analyzed using x-ray diffraction. The results suggested that the protective coating with multilayer structure was dense and homogeneous. The formation of Cr inner diffusion layer was beneficial to the bonding strength between the coating and substrate, which was attributable to the double glow technology. The oxidation behaviors of Al/Cr coating were investigated by the isothermal oxidation tests for 100 h at 700 °C, 800 °C and 900 °C, respectively. The results indicated that the protective coating showed a lower oxidation rate. At 700 °C, the Al _2 O _3 oxidation products were formed on the surface of coating at high temperature, which were dense and homogeneous against oxygen diffusion. With the increase of oxidation temperature, the external diffusion of Cr element reacted with oxygen to form Cr _2 O _3 , which provided the further protection. As for 900 °C, the volatile CrO _3 was formed by the reaction of the external diffusion of Cr and Cr _2 O _3 , and the oxidation products Al _2 O _3 and Cr _2 O _3 continued to provide protection for Ti2AlNb alloy.

Keywords

• Al/Cr coating
• Ti2AlNb alloy
• Oxidation behaviors
• Double glow technique