Influence of interstitial impurities on the valence electron structures and phase transformation behavior in intermediate Ti–Al alloys

Development of intermetallic compounds in Ti–Al alloys for high-temperature structural applications has long been impeded due to their embrittlement. To overcome the embritttlement, it is necessary to understand thoroughly its chemical bonding nature and the resultant phase transformation behavior. In this study, based on the Empirical Electron Theory of Solids and Molecules (EET), effects of interstitial impurities on the valence electron structures and phase transformations in the intermediate Ti–Al alloys were investigated. It was demonstrated that for such alloy systems, because interstitial impurities can enhance the hybridization states of Ti and Al atoms, the valence electron structures of various phases became considerably anisotropic. As a result, some phase transformations at high temperatures was hindered, leading to the occurrence of complex metastable phases at the room temperature. Such theoretical calculations clarified some unclear results from experimental observations in the literature.