Improvement of the oxidation resistance of TiAl alloys by using the chlorine effect

Most TiAl alloys lack from their insufficient oxidation resistance in air at temperatures above 800°C. Recently it has been found that small amounts of Cl in the alloy may significantly improve the oxidation resistance. However, the mechanisms responsible for this effect were not yet understood. In the paper oxidation experiments with TiAl alloys are reported where Cl was alloyed to the material by the P/M route or applied to the material surface either by ion implantation or by PVD. The results of the investigations revealed that the Cl-effect is due to the formation of volatile metal chloride species. It is shown that chlorine can have a beneficial effect on oxidation resistance in a certain Cl-range which is quantified by thermodynamic calculations. It is assumed that the Cl-effect offers a significant potential for improvement of the oxidation resistance of technical TiAl alloys.