ToF-SIMS Study on the Initial Stages of the Halogen Effect in the Oxidation of TiAl Alloys

Intermetallic titanium aluminide samples implanted with fluorine using plasma immersion ion implantation were investigated after high-temperature exposure for short times at 500 and 900 °C in air by ToF-SIMS as a surface analytical method. The ToF-SIMS method was applied in order to obtain information regarding the location of fluorine with respect to the oxide layer formed and the substrate after ion implantation and after high-temperature exposure, respectively. The aim of the present work was to obtain further insight into the mechanisms active during the initial stages of oxidation. The scale structure in the initial oxidation phase consists of titanium and aluminum oxides/fluorides/oxyfluorides. The arrangement of their layered structure can be interpreted according to their thermodynamic stabilities in the partial pressure gradient of oxygen over the scale and according to the metal activities and the presence of fluorine at the metal/scale interface.