Oxidation behaviour of a fluorinated beta-stabilized γ-TiAl alloy with thermal barrier coatings in H2O- and SO2-containing atmospheres

• A bond coat-free thermal barrier coating-system on γ-TiAl was investigated.
• A surface treatment with fluorine provides a thermally grown oxide scale.
• Lifetimes exceed 1000 cycles of 1 h dwell time at 900 °C in H2O/air and SO2/air.
• No spallation of ceramic topcoat after thermal exposure.
• The fluorine concentration is maintained after long-term exposure.

The oxidation behaviour of a novel thermal barrier coating (TBC) system on a β-stabilized TiAl alloy was investigated at 900 °C in air containing water vapour and sulphur dioxide. This recently developed system consists of a 7 wt.% yttria partially stabilized zirconia topcoat deposited on fluorine-treated and pre-oxidized TNM-B1 substrate material. During thermal cycling at 900 °C in atmospheres containing either 10 vol.% H2O or 0.5 vol.% SO2, no spallation of the TBCs was observed for exposure periods exceeding 1000 cycles of 1 h dwell time. Fluorinated samples without TBCs showed similar oxidation behaviour, whereas the untreated TNM-B1 alloy revealed significant oxidation.