High-temperature synchrotron X-ray diffraction study of phases in a gamma TiAl alloy

Results on high-resolution synchrotron X-ray diffraction, optical microscopy and scanning electron microscopy are presented for a Ti-46Al-1.9Cr-3Nb (at.%) alloy at room temperature and at elevated temperature. The phase equilibria for the composition of the alloy have been calculated and have been found to correspond perfectly well to the molar phase fractions for γ, α2 and B2 phases, which were for the first time derived from the fitting procedure of the diffraction patterns at elevated temperatures. Thermal expansion coefficients and relative volume change for the major γ and α2 phases have been independently determined. X-ray diffraction and microscopy data prove the presence of oxidation at temperatures above about 1100 deg. C, with formation of Ti2O and Al2O3 oxides