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

The phase stability and transformations in Al-3(Ti1-xZrx) intermetallic alloys (x = 0-1) produced by arc melting were studied in the temperature range of 20 to 1100degreesC by using an in situ X-ray diffraction (XRD) method. Two phases, D0(22) and D0(23), 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 D0(23) phase was detected. For the alloy with x = 0.32, the D0(23) transformed to D0(22) on heating at temperatures 1100 degreesC and above. On cooling, the D0(22) phase was stable to similar to 650 degreesC, and the D0(23) phase was formed again in the temperature range of 600-650 degreesC. The positional parameters of the D0(23) atomic structure in the alloy Al-3(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 D0(23) structure. Zr fractions as small as x = 0.1 are required to stabilize the D0(23) structure. A low temperature phase modification, Al24Ti8, was also detected in the surface layer in the temperature range below 650degreesC and it was found to be a result of surface grinding. Mechanical properties of the alloys studied are also discussed. (C) 2003 Elsevier Science Ltd. All rights reserved.