Thermal and structural stability of Zr-based amorphous thin films for potential application in hydrogen purification

Amorphous alloys are of particular interest due to their less susceptibility to hydrogen embrittlement and corrosion, superior mechanical properties and more importantly lower cost compared to the Pd-based crystalline membranes. Amorphous thin films of Zr40.5Ni59.5, Zr56.2Cu43.8, Zr30Cu57.7Y12.3, and Zr32Cu57.3Ti10.7 alloys are fabricated by the magnetron sputtering method. All alloys are thermally stable until above 400 °C under an inert atmosphere. Nevertheless, the thermal stabilities of all alloys are reduced by almost more than 150 °C under hydrogen with exception of the Zr40.5Ni59.5 alloy showing comparable thermal stability under hydrogen and inert. Structural analyses by XRD under hydrogen and an inert atmosphere reveal decomposition of the studied amorphous alloys during the crystallisation process, leading to severe phase separation for Ni and Cu in Zr40.5Ni59.5 and Zr56.2Cu43.8 alloys. Such a phase separation seems to have an influence on the crystallisation path and products. However, Cu phase separation seems to be mitigated in Zr30Cu57.7Y12.3, and Zr32Cu57.3Ti10.7 alloys despite their higher Cu content compared to Zr56.2Cu43.8 alloy. The surface segregation tendency of Cu results in surface crystallisation in the Zr56.2Cu43.8 alloy, whilst bulk nucleation and growth dominates the crystallisation process in the other alloys, evident by the non-isothermal kinetic studies. The calculated activation energies show that more energy is required for nucleation compared to the growth process in the Zr40.5Ni59.5 and Zr56.2Cu43.8 alloys, whilst is the opposite case in Zr30Cu57.7Y12.3, and Zr32Cu57.3Ti10.7 alloys.