The oxidation characteristics of Ti-14Al-21Nb (mass%) were studied in a temperature range 1000K to 1300K in O
2, N
2-21 vol%O
2 and Ar-21 vol%O
2 under atmospheric pressure. The oxidation rates in N
2-O
2 are lower than those in O
2. The oxidation rates in Ar-O
2 are almost equal to those in N
2-O
2 below 1200K. However, at 1300K the oxidation rate in Ar-O
2 is nearly equal to that in O
2. The oxidation curves are almost parabolic, except for those in O
2 and Ar-O
2 at 1300K, for which temporal acceleration was observed. The scale consists of three layers: outermost layer of sintered rutile grains, intermediate alumina rich layer, and innermost layer consisting of a mixture of rutile, alumina and niobium oxide grains. In N
2-O
2, a nitride layer (TiN), an Nb-rich layer (Nb
2Al) and an Al-rich layer (TiAl) are additionally formed in this order beneath the three layered scale. These differences in the oxidation characteristics are attributable to the folowing observations;
1. A more continuous alumina rich layer is formed because of the reduced oxygen pressure below 1200K.
2. A continuous TiN layer is formed near the scale/substrate interface.
3. By the selective nitridation of Ti near the scale/substrate interface, Al is enriched beneath TiN, and TiAl is formed.
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