Influence of Moisture on the oxidation of γ‐TiAl

Abstract

The influence of water vapour on the oxidation of Ti-50 at.'% Al was studied a t 900"C.Thick. well-adherent oxide scales were formed consisting of an outer TiO, layer and an inner heterogeneous mixture of Ti02 and A1203. The interface between these layers is marked by large pores and A1202 particles embedded in TiOz. No compact Al2O3 barrier layer was observed. The oxidation leads to formation of a two phase. oxygen enriched subsurface zone, which is Al-depleted by inncr oxidation of A1 to Al2O3.The oxidation kinetics were followed by continuous thermogravimetry. Exposure in moist oxygen leads to an accelerated attack compared with oxidation in dry oxygen. In moist oxygen the rate is linear after a short transition period. The oxidation rate is influenced by water partial pressure and oxygen partial pressure.Der EinfluB von Wasserdampf auf die Oxidation von Ti-SO At.% A1 wurde bei 900°C untersucht. Es entstehen mehrlagige,gut haftende Oxidschichten, die sich aus ciner luReren Ti02-Schicht und einem inneren, heterogenen Gemenge aus Ti02 und A1203 zusammensctzen. Zwischen diesen beiden Teilschichten befinden sich A1203-Partikcl cingebettct in poriisem TiOz. Eine kompakte Alz03-Barriereschicht wurde nicht beobachtel. Die Oxidation l'iihrt zu einer zweiphasigen, sauerstoffreichen Metallrandzone, die aufgrund einer inneren Oxidation von Al zu A1203 an Alverarmt ist.Die Kinetik der Oxidation wurde kontinuicrlich thcrmogravimetrisch bestimmt. Die Auslagerung in feuchtem Sauerstoff fuhrt zu cinem im Vcrgleich zur Oxidation in trockenein Sauerstoff beschleunigten Angriff. In feuchtcm Sauerstoff @lgt die Oxidation einem linearen Zeitgesetz nach eincr kurzen Ubergangsperiode. Die Oxidationsgeschwindigkeit wird vom Wasserund Sauerstoffpartialdruck heeinflu8t.

Improvement of the oxidation behaviour of TiAl-alloys by treatment with halogens

“…The halogen effect works also in wet environments where the oxidation rate is normally increased [20]. The rutile in the mixed oxide scale formed on the untreated alloys reacts with the water molecules releasing hydrogen which deteriorates the oxide.…”

Water vapor effect on high-temperature oxidation behavior of Fe3Al intermetallics

“…Water vapor also affects the selective oxidation of aluminum from TiAl [46]. • Water vapor can affect diffusion of species through oxides such as SiO 2 [41] by changing the network structure [47].…”

Some water vapor effects during the oxidation of alloys that are α-Al2O3 formers

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] Most of these effects are detrimental in that the oxidation rates are increased. The effect of water vapor on the oxidation of alloys that develop oxidation resistance via the formation of continuous ␣-Al 2 O 3 scales is important because numerous high-temperature alloys and coatings rely on such a selective oxidation process for oxidation resistance.…”