The influence of Zr alloying on the structure and properties of Al3Ti

The phase stability and transformations in Al3(Ti1-xZrx) intermetallic alloys (x=0–1) produced by arc melting were studied in the temperature range of 20 to 1100°C by using an in situ X-ray diffraction (XRD) method. Two phases, D022 and D023, both having ordered tetragonal structures, were present at room temperature at zirconium concentrations from 1 to 10 at.% (x =0.04–0.4). At higher concentrations of Zr (0.4<x<1), only the DO23 phase was detected. For the alloy with x=0.32, the D023 transformed to D022 on heating at temperatures 1100 °C and above. On cooling, the D022 phase was stable to ∼650 °C, and the D023 phase was formed again in the temperature range of 600–650 °C. The positional parameters of the D023 atomic structure in the alloy Al3(Ti0.68Zr0.32) were determined using a full-profile XRD analysis. It was shown that zirconium atoms substitute titanium atoms and increase the lattice parameters of the D023 structure. Zr fractions as small as x=0.1 are required to stabilize the D023 structure. A low temperature phase modification, Al24Ti8, was also detected in the surface layer in the temperature range below 650°C and it was found to be a result of surface grinding. Mechanical properties of the alloys studied are also discussed.