Abstract
The effect of Ag additions on the oxidation behavior of γ-TiAl hasbeen studied. The materials investigated containing 47–50 at.% Aland 0–5 at.% Ag were tested with respect to oxidation resistanceduring exposure in air at 800°C. The exposures up to around 1600 hrshowed that suitable Ag additions can promote formation of long-term,protective, alumina scales on γ-TiAl alloys. Extensive analysesof the oxidation products using optical metallography SEM, XRD, EPMA,and SIMS revealed that Ag stabilizes the Z-phase (Ti5Al3O2) in thesubscale-depletion layer thereby preventing formation of α2-Ti3Alas well as Ti-rich nitrides, which are responsible for the destructionof alumina scales in common γ -TiAl alloys. The best results wereobtained for the alloy Ti–50Al–2Ag; even during exposures aslong as around 1600 hr, this alloy still appeared to form a stable aluminalayer. It was found that high Ag additions of 5% were detrimental afterlonger exposure times due to extensive Ag precipitationat the interface between the alloy and depletion layer, resulting inlocalized formation of rapidly growing, mixed-oxide scales.
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Shemet, V., Tyagi, A.K., Becker, J.S. et al. The Formation of Protective Alumina-Based Scales During High-Temperature Air Oxidation of γ -TiAl Alloys. Oxidation of Metals 54, 211–235 (2000). https://doi.org/10.1023/A:1004694111032
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DOI: https://doi.org/10.1023/A:1004694111032