X-ray high-temperature in situ investigation of the aluminide TiAl2 (HfGa2type)

X-ray high-temperature powder diffraction investigations were made in situ on the aluminide TiAl2 (Pearson symbol tI24, space group 14(1) /and, HfGa2 type) in the temperature range 20-763 degrees C. The unit cell parameters a nd the unit cell volume increase linearly with temperature. whereas the axi al ratio cia hardly changes with temperature. Metallographical and X-ray po wder diffraction investigations on the heat-treated and subsequently quench ed alloys show that TiAl2, is stable up to 1200 degrees C. In the as-cast a lloy TiAl2,, a metastable orthorhombic modification TiAl2(m) has been obser ved (oC12, Cmmm, ZrGa2 type). X-ray powder diffraction data for the stable TiAl2 modification are presented. (C) 2000 Elsevier Science S.A. All rights reserved.