Isothermal oxidation behavior of experimental Ti−Al−Si alloys at 700 °C in air

Abstract

In the present work the oxidation kinetics of a series of experimental Ti−Al−Si based alloys, additionally alloyed by zirconium and tin, was studied upon isothermal exposure at 700 °C in ambient air and compared with that of a commercially available Ti−6242 alloy. Examinations of the oxide scale microstructure, its phase composition and crystal morphology along with the measurements of the alpha-case thickness were performed in order to elucidate the oxidation mechanism of Ti−Al−Si based alloys. The oxidation rates of the experimental alloys obeyed a parabolic relationship and were 1.5–2 times lower than those of the reference Ti−6242 alloy. The alloying of the base Ti−6Al−1.4Si alloy with zirconium strongly reduced its oxidation rate, while the effect of tin addition appeared to be slightly deleterious. The zirconium addition reduced the thickness of the oxide scale and hindered recrystallization of the rutile crystals in the surface oxide layer. At the same time, the additional alloying with tin had practically no effect on the size of rutile crystals. The thickness of alpha-case was found to depend on the oxidation dwell time and followed a parabolic relationship. The most noticeable effect in reducing the alpha-case thickness was provided by zirconium addition, while the effect of additional alloying with tin on alpha-case was slightly unfavorable.