OXIDATION CHARACTERISTICS OF TI-25AL-10NB-3V-1MO

Static oxidation kinetics of Ti-25Al-10Nb-3V-1Mo (atomic percent) were investigated in air over the temperature range of 650-1000-degrees-C using thermogravimetric analysis. The oxidation kinetics were complex at all exposure temperatures and displayed up to two distinct stages of parabolic oxidation. Breakaway oxidation occurred after long exposure times at high temperatures. Oxidation products were determined using x-ray diffraction techniques, electron microprobe analysis, and energy dispersive x-ray analysis. Oxide scale morphology was examined using scanning electron microscopy of the surfaces and cross-sections of oxidation specimens. The oxides during the parabolic stages were compact and multilayered, consisting primarily of TiO2 doped with Nb, a top layer of Al2O3 and a thin bottom layer of TiN. The transition between the first and second parabolic stage is linked to the formation of a TiAl layer at the oxide-metal interface. Porosity also formed in the TiO2 layer during the second stage, causing degradation of the oxide and breakaway oxidation.