FUNDAMENTALS OF TIAL OXIDATION - A CRITICAL-REVIEW

The paper critically reviews the state of the art on the oxidation of TiAl. At the beginning differences compared to the oxidation of conventional Fe, Ni and Co alloys are discussed. The knowledge of the Ti-Al-O phase diagram as a basis for an understanding of the processes occurring during oxidation is very incomplete. Three different scale structures can be distinguished as functions of time or scale thickness. In the sub-surface zone two phases with high oxygen solubilities can be identified after a certain time. These phases do not follow from the existing phase diagram. Nitrogen can have two different effects depending on the time it is added to the oxidation environment. The micro-structure also affects the oxidation behaviour significantly, so this effect can lead to a misinterpretation of the influence of other parameters such as alloying elements. The influence of alloying elements is not yet understood. Mechanical loading leads to scale cracking, however, the system has a significant scale repair capacity, though about two-thirds of the scale grows by inwards transport.