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 conven tional 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 occur ring during oxidation is very incomplete. Three different scale struct ures can be distinguished as functions of time or scale thickness. In the sub-surface zone two phases with high oxygen solubilities can be i dentified after a certain time. These phases do not follow from the ex isting phase diagram. Nitrogen can have two different effects dependin g on the time it is added to the oxidation environment. The micro-stru cture also affects the oxidation behaviour significantly, so this effe ct can lead to a misinterpretation of the influence of other parameter s 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-t hirds of the scale grows by inwards transport.