The crystal structure, microhardness and thermal stability of the Ti26Al55Zn19 alloy

Ti is usually added into aluminum–zinc alloys to refine the grains and improve plasticity and strength. However, the precipitated phases and the mechanism of grain refinement were not fully understood. In this study, a new ternary phase τ–Ti26Al55Zn19 was found, which formed by the diffusion of Zn atoms into TiAl3 phase. Its crystal structure has been investigated by high resolution X-ray diffraction (HRXRD) and high resolution transmission electron microscopy (HRTEM). The Rietveld refinement results show that the structure of τ–Ti26Al55Zn19 phase is an ordered face centered cubic with Ti atoms occupying 1a (0, 0, 0) positions and Al/Zn atoms occupying 3c (0, 0.5, 0.5) positions. The crystal structure is interpreted well with the selected area electron diffraction patterns and high resolution electron microscopy images. The microhardness value of Ti26Al55Zn19 was less than that of TiAl3 owing to the structure transformation. The curves observed from simultaneous thermogravimetric (TG) – differential scanning calorimetric (DSC) analyzer indicated that the τ–Ti26Al55Zn19 phase was stable up to 810.9 °C, but above this temperature TiAl3 phase appeared from the liquid with the volatilization of Zn.