Influence of Si and W additions on high temperature oxidation of gamma,alpha(2) Ti-Al alloys

Titanium aluminides have potential interest for high temperature applications because of their low density and high temperature strength. In this study the isothermal oxidation behavior in air and in the temperature range 700-850 degrees C of gamma-alpha(2)Ti-Al bulk alloys with different additions of W (0-9.5 wt.%) and Si (0-5.0 wt.%) was investigated. The samples were prepared by are-melting starting from pure element powders (99.99%). After thermal treatments, for homogenisation and phase stabilisation, the samples were tested using a thermal analysis apparatus in order to evaluate their oxidation resistance. The oxidation rates show the beneficial effect of the W and Si additions. The growth and adherence of the protective scale on alloys have been investigated in conjunction with detailed oxide scale characterisation using the techniques of scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results of the study are used for critical assessment of the oxidation mechanisms leading to the formation of surface layers of different compositions.