Effects of Ga and Sn Additions on the Creep Strength and Oxidation Resistance of Near-α Ti Alloys

Abstract

The effects of Ga and Sn additions, with an almost constant value regarding Al equivalence, on the creep properties and oxidation resistance of the near-α Ti alloy Ti-5Al-4Zr-1Mo were investigated. The creep strain rate increased due to the replacement of Sn with Ga, which was accompanied by an increase in the volume fraction of primary equiaxed α phase. In addition, the replacement of Sn with Ga decreased the activation energy of the steady-state creep rate for the similar volume fraction of the equiaxed α phase. Ga addition improved the oxidation resistance without Ga segregation at the TiO2/substrate interface, whereas Sn promoted oxide spallation with metallic Sn segregation at the interface. Ga uniformly dissolved into the internal TiO2 and into the external Al2O3 as a result of solid solution formation between Ga2O3 and the aforementioned oxides, which suppressed oxide growth. The formation of (GaAl)2TiO5 in TiO2 and Al2O3 was also discussed on the basis of the phase relationships in the TiO2-Al2O3-Ga2O3 system.