Oxidation kinetics and mechanisms of Ti-Ta alloys

The oxidation kinetics of alloys containing nominally 5, 40, and 60 weight percent Ta, as well as pure Ti and Ta, were measured for 16 hr in argon-20% oxygen or pure oxygen at 800, 1000, 1200 and 1400 degrees C. These three alloys were chosen as representative of low, intermediate and high-Ta content for comparison to previous studies. In addition to TGA, specimens were examined using scanning electron microscopy, electron microprobe, and X-ray diffraction. The effect of Ta on the oxidation of Ti is explained by an increase in the compositional range of the oxygen-stabilized alpha-phase while apparently reducing the solubility of oxygen and the diffusivity of Ti in both the alpha- and beta-phases. The composition which exhibits the minimum oxidation rate varies depending on the temperature and atmosphere, but is governed by the solubility of Ta in oxygen-stabilized,alpha-Ti.