TEM study of the initial oxide scales of Ti2AlC

This paper presents a detailed microstructural analysis of the crystallographic relationships between alpha-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 degrees C. It is shown that the alpha-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 alpha-Al2O3 layer. The channels for inward diffusion of O and outward diffusion of Ti and Al run not only along grain boundaries of alpha-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 alpha-Al2O3 oxide scale and Ti2AlC were observed: [(1) over bar 1 2](alpha-Al2O3) // [0 1 0](Ti2AlC), (1 1 0)(alpha-Al2O3) // (0 0 1)(Ti2AlC) and [0 0 1](alpha-Al2O3) // [3 3 1](Ti2AlC), (1 1 0)(alpha-Al2O3) // (1 (1) over bar 0)(Ti2AlC). (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.