TEM study of the initial oxide scales of Ti2AlC

This paper presents a detailed microstructural analysis of the crystallographic relationships between α-Al2O3 oxide scale and Ti2AlC parent material, and examines the atomic diffusion and formation of oxide scale on Ti2AlC during the initial oxidation stage at 1200 °C. It is shown that the α-Al2O3 oxide scale can be either a continuous or a discontinuous capping layer on Ti2AlC. A Ti-rich intermediate layer that consists mostly of TiC interrupts the continuity of the α-Al2O3 layer. The channels for inward diffusion of O and outward diffusion of Ti and Al run not only along grain boundaries of α-Al2O3, 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 Ti2AlC. Crystallographic orientation relationships between α-Al2O3 oxide scale and Ti2AlC were observed: [1¯12]α-Al2O3 // [010]Ti2AlC, (110)α-Al2O3 // (001)Ti2AlC and [001]α-Al2O3 // [331]Ti2AlC, (110)α-Al2O3 // (11¯0)Ti2AlC.