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

Abstract

Non-isothermal oxidation is one of the important issues related to the safe application of high-temperature titanium alloys, so this study focuses on the non-isothermal oxidation behavior and mechanism of near-α titanium alloys. The thermogravimetry-differential scanning calorimetry (TGA/DSC) method was used to study the non-isothermal oxidation behavior of TA29 titanium alloy heated from room temperature to 1450 °C at a heating rate of 40 °C/min under pure oxygen atmosphere. The results show that non-isothermal oxidation behavior can be divided into five stages, including no oxidation, slow oxidation, accelerated oxidation, severe oxidation and deceleration oxidation; for the three-layer TiO2 scale, Zr, Nb, Ta are enriched in the intermediate layer, while Al is rich in the inner layer and Sn is segregated at the oxide-substrate interface, which is related to their diffusion rates in the subsurface α case. The oxidation mechanism for each stage is: oxygen barrier effect of a thin compact oxide film; oxygen dissolution; lattice transformation accelerating the dissolution and diffusion of oxygen; oxide formation; oxygen barrier effect of recrystallization and sintering microstructure in outer oxide scale. The alloying elements with high valence state and high diffusion rate in α-Ti are favorable to slow down the oxidation rate at the stage governed by oxide formation.

Non-Isothermal Oxidation Behaviors and Mechanisms of Ti-Al Intermetallic Compounds

“…Similar to the near-α titanium alloy TA29 [23], the oxidation mass gains of the Ti-46Al-2Cr-5Nb and Ti-24Al-15Nb-1.5Mo alloys at Stage I were very small and could be neglected (Figure 3), which is ascribed to the fact that a thin titanium oxide film (200 nm) rapidly forms on the alloys at room temperature and passivates the surface [14].…”

“…Furthermore, based on the Fick’s diffusion law and assuming that the diffusion of specie A satisfies Arrhenius kinetics, the relationship among the temperature, the mass gain and the oxidation activation energy of the Ti-Al alloys can be derived, as shown in Equation (1). Details for the derived process can be seen in our previous work [23]. −lnnormaldfalse(Δmfalse)normaldT−lnfalse(Δmfalse)=−lnK*+E/normalRT where Δ m is the mass gain per unit area, E is the oxidation activation energy, R is the molar gas constant and K* is constant.…”

“…TGA/DSC simultaneous thermal analysis is a common method to study the non-isothermal oxidation behaviors of metals and their alloys [20,21,22,23]. Adopting the TGA/DSC method, G.B.…”

“…The results showed that when the Cr content exceeds 10–15 wt.%, the oxidation resistance of Ti-Cr alloys increases with the Cr content due to the precipitation of Cr oxide [22]. Ouyang et al [23] carried out a research on the non-isothermal oxidation behaviors of a high-temperature near-α titanium alloy (TA29 alloy), meanwhile discussed the effects of lattice transformation and alloying elements on the non-isothermal oxidation behaviors of the TA29 alloy.…”

Effect of Nb Content on Cyclic Oxidation Behavior of As-Cast Ti-1100 Alloys

“…With the development of aircraft toward high flight speeds, in addition to low density and high strength, titanium alloys are also required to withstand higher temperatures. While a limitation of developing near-α titanium alloy is that the high temperature oxidation resistance is significantly reduced when the temperature exceeds 600 • C, the severe surface oxidation of high-temperature components of aeroengine will result in the decrease of effective load bearing area, which causes structure failure [5,6]. Previous investigation has reported that adding Nb to titanium alloy could improve the high temperature oxidation resistance and mechanical properties [7].…”