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-a 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 a 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 a phase. Ga addition improved the oxidation resistance without Ga segregation at the TiO 2 /substrate interface, whereas Sn promoted oxide spallation with metallic Sn segregation at the interface. Ga uniformly dissolved into the internal TiO 2 and into the external Al 2 O 3 as a result of solid solution formation between Ga 2 O 3 and the aforementioned oxides, which suppressed oxide growth. The formation of (GaAl) 2 TiO 5 in TiO 2 and Al 2 O 3 was also discussed on the basis of the phase relationships in the TiO 2 -Al 2 O 3 -Ga 2 O 3 system.

Non-Isothermal Oxidation Behavior and Mechanism of a High Temperature Near-α Titanium Alloy

“…Hence, a small amount of Al decreases the oxidation resistance of TA29 alloy. As for the segregation of Sn at the oxide-substrate interface, on the one hand, it increases the vacancy concentration in the alloy, promoting the diffusion of Ti atoms in the alloy; on the other hand, it reduces the adhesion between the oxide scale and the substrate, prompting the oxide scale to peel off [38,39,40]. Both intensify the reaction between Ti and O and decrease the oxidation resistance of the alloy, thus Sn is detrimental to the oxidation resistance of TA29 alloy.…”

Role of refractory elements in near-alpha titanium alloys on high temperature mechanical properties

“…Conventional near-alpha Ti alloys are strengthened by fine alpha2 phase with DO 19 structure and intermetallic silicides [7][8]. Up to now, numerous works were focused on the influence of alpha stabilizing alloying elements such as Ga, Sn, Hf and Zr on the high temperature mechanical properties of the near-alphaa titanium alloys [9][10]12]. These studies demonstrated that the solid solution strengthening and the formation of a 2 phase are effective in improving high temperature strength, but degrade the ductility of the material [10][11] probably due to the lower symmetry of its DO 19 crystal structure.…”

“…Up to now, numerous works were focused on the influence of alpha stabilizing alloying elements such as Ga, Sn, Hf and Zr on the high temperature mechanical properties of the near-alphaa titanium alloys [9][10]12]. These studies demonstrated that the solid solution strengthening and the formation of a 2 phase are effective in improving high temperature strength, but degrade the ductility of the material [10][11] probably due to the lower symmetry of its DO 19 crystal structure. The effect of silicon addition was also extensively studied to increase high temperature tensile and creep strength of near-a and a+b titanium alloys [9,[13][14].…”

Effect of α₂ Precipitation on Creep and Tensile Properties of Ga-Added Near-α Titanium Alloys

“…It is well known that these mechanical properties are also dependent on factors of microstructure morphology such as the volume fraction and size of equiaxed α, the thickness of lamellar, etc. Some authors have shown that creep strength is strongly dependent on the volume fraction of equiaxed α in the bimodal microstructure of Ga and/or Sn added near-α alloys with an almost constant value of Al equivalence [9]. In this study, the volume fraction of equiaxed α was set to be similar in the bimodal microstructure.…”

“…Our previous work showed that room temperature tensile elongation drastically decreased at around 9 to 11 of Al equivalence for a bimodal microstructure of multi-component Ti alloys produced at the National Institute for Materials Science (NIMS) in Japan (for examples, see Kitashima et al [6][7][8][9]). In addition, the minimum creep strain rate decreased with increasing Al equivalence especially between 9 and 11 of Al equivalence due to the formation of α 2 precipitate [8].…”