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Initial Oxidation Behavior in Air of TiAl-2Nb and TiAl-8Nb Alloys Produced by Electron Beam Melting

Titanium aluminide alloys are good candidates for structural applications thanks to their low density and good balance of properties up to relatively high temperatures. However, their application is still limited by significant oxidation. Four γ-TiAl alloys with different content of aluminum and niobium were produced by electron beam melting: Ti-45Al-2Cr-2Nb, Ti-48Al-2Cr-2Nb, Ti-45Al-2Cr-8Nb, and Ti-46Al-2Cr-8Nb. The behavior of these alloys in response to oxidation in air during constant heating up to 1000 °C and isothermal oxidation for 10 h at 850 and 950 °C were studied by thermogravimetric analysis. The mass gain due to oxidation of the low Nb-containing alloys was always at least twice that of the high Nb-containing alloys. Both low and high Nb-containing alloys exhibited on their surface oxidation products of the same nature: oxides TiO2 and Al2O3, and nitrides TiN and Ti2AlN. Niobium addition up to 8 at.% did not suppress the growth of rutile and promote the formation of a protective alumina layer. However, it efficiently reduced the formation of rutile, mainly responsible for the mass gain due to oxidation of γ-TiAl alloys and with tendency to spallation.
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