Formation of the amorphous phase in Zr 2Al by hydrogen absorption and the effects of titanium substitution on the amorphization behaviour

Abstract

To explore the hydrogen-induced amorphization behaviour of Zr 2Al (Ni 2In type), the structural changes of the compound during hydrogen absorption are investigated by means of X-ray diffraction (XRD), transmission electron microscopy (TEM) and differential thermal analysis (DTA). To examine the effects of alloying element substitution, small amounts of zirconium are replaced by titanium, which has similar chemical and physical properties. At low reaction temperatures, the Zr 2Al and (Zr 0.85Ti 0.16) 2Al compounds form crystalline hydride phases with orthorhombic structure initially, and then transform to an amorphous phase gradually. However, at higher temperatures they are decomposed into the stable phases ZrH 2 and Zr 3Al 2. For the titanium-containing alloy, the reaction process and the amorphization mechanism are similar to those of the titanium-free alloy system. The amorphization temperature is increased by the titanium substitution, which is considered as being due to the increase of the elastic modulus owing to the titanium addition. It is suggested that the hydrogen-induced amorphization occurs as a result of the suppression of the decomposition of the crystalline hydride phase into the stable configurations, and the amorphization mechanism is the short-range motion of aluminum atoms.