TEM study of the initial oxide scales of Ti_2AlC

摘要

This paper presents a detailed microstructural analysis of the crystallographic relationships between α-Al_2O_3 oxide scale and Ti_2AlC parent material, and examines the atomic diffusion and formation of oxide scale on Ti_2AlC during the initial oxidation stage at 1200 °C. It is shown that the α-Al_2O_3 oxide scale can be either a continuous or a discontinuous capping layer on Ti_2AlC. A Ti-rich intermediate layer that consists mostly of TiC interrupts the continuity of the α-Al_2O_3 layer. The channels for inward diffusion of O and outward diffusion of Ti and Al run not only along grain boundaries of α-Al_2O_3, but also through the Ti-rich intermediate layer. The outward diffusion of Al atoms is either parallel to the (0 0 1) basal plane or parallel to prism planes of Ti_2AlC. Crystallographic orientation relationships between α-Al_2O_3 oxide scale and Ti_2AlC were observed: [1-bar 12]_(α-Al_2O_3) // [010]_(Ti_2AlC), (110)_(α-Al_2O_3) // (001)_(Ti_2AlC) and [001]_(α-Al_2O_3) //[331]_(Ti_2AlC),(110)_(α-Al_2O_3)// (11-bar 0)_(Ti_2AlC).