Oxidation behavior and effect of oxidation on microstructure and tensile properties of Ti-5Al-5Mo-5V-1Cr-1Fe alloy

In this study, both oxidation behavior and tensile properties of Ti-5Al-5Mo-5V-1Cr-1Fe alloy are investigated in air between 100 °C and 1000 °C. X-ray diffraction and light optical microscope are used to characterize the phase composition and morphology of oxide layers, respectively. The mixed oxide layer consists of the white TiO₂, the golden TiO and blue Ti₂O₃, with white TiO₂ being the dominant oxide phase. These colored titanium oxides result in different colors on the surface of the specimens. The oxidation has a significant effect on the tensile properties of the alloy. Both adherent oxide layer and stable microstructure of adequate equiaxed α phase within a fine β transformed matrix are primarily responsible for a good combination of strength and ductility below 750 °C. However, as the alloy oxidized above 750 °C, both strength and ductility decrease dramatically due to the formation of defective oxide layer and coarsed β grains. An reliable oxidation model is proposed to predict the thickness of the oxide layer after taking the spalled oxide layer thickness into account. Moreover, the spallation of oxide layer leads to a fracture mode change from ductile fracture in specimens with dense oxide layer to a mixture of ductile fracture and brittle intercrystalline fracture in specimens with defective oxide layer.