Hydrogenation and its effect on the crystallisation behaviour of Zr55Cu30Al10Ni5 metallic glass

Zr55Cu30Al10Ni5 metallic glass exhibits high thermal stability, and as it c ontains early and late transition metal elements (ETM/LTM) it is of interes t to study its hydrogenation properties. Charging melt-spun ribbons electro chemically to different hydrogen-to-metal (H/M) ratios and following the ef fusion of hydrogen by thermal desorption analysis (TDA) reveals hydrogen de sorption from high interstitial-site energy levels at temperatures below 62 3 K. Zirconium hydrides are formed above 633 K. At higher temperatures part ial desorption of hydrogen occurs. Simultaneously, transformation to differ ent hydride phases takes place in the order tetragonal epsilon-Zr-hydride, cubic delta-Zr-hydride and a mixture of (alpha + beta)-Zr-hydride. Thermal stability investigations by differential scanning calorimetry (DSC) point o ut the exothermic peaks of formation/transformation to different Zr-hydride phases. The formation of zirconium hydride causes depletion in the number of free Zr atoms leading, in turn, to different crystalline phases upon cry stallisation. X-ray diffraction (XRD) reveals the formation of different cr ystalline phases for different H/M ratios. For a H/M-ratio of 0.37 a hexago nal AlZr2 phase forms at 753 K, whereas for high hydrogen contents of 0.7<H /M<1 cubic AlCu2Zr forms already at 713 K. In contrast, the uncharged ribbo ns crystallise at 771 K by formation of a mixture of metastable fee NiZr2-t ype phase, orthorhombic NiZr and tetragonal CuZr2 phases. (C) 2000 Elsevier Science S.A. All rights reserved.