Study On The Property And Structure Evolution Of Pd-based Metallic Glasses By Synchrotron

Glass transition phenomenon is one of the oldest but still puzzled questions.Many dynamical heterogeneity properties in the vicinity of glass transition temperature are believed to be closely related to the structure variation.Whether the glass transition is a pure dynamical problem or is a structural related problem that has a thermodynamic requirement,is still debatable.However,no clear experimental result so far has captured the specific structure transition around the glass transition temperature T_g.Bulk metallic glass is a new type of amorphous material that has been rapidly developed in recent years.It is not only a novel material with special properties,but also an important model system for studying amorphous structure.In this study,taking advantages of in-situ high-energy synchrotron X-rays diffraction technique,the details of structure change in two Pd-based metallic glass samples were revealed by carefully examining their total scattering structure function S?Q?and pair distribution function G?r?.By examing the peak height,peak full width at half maximum?FWHM?changes of the first sharp diffraction peak?FSDP?and shoulder peak on the second peak of S?Q?functions of Pd40.5Ni40.5P19,Pd81Si19 and Pd40.5Ni40.5P14Si5 metallic glass at different temperatures,an structure change,which is close to Kauzmann temperature T_k,was observed.This provides evidence for possible the phase transition aroud T_g.The size of the varied structure of Pd_40.5Ni_40.5P₁₉ metallic glass was roughly estimated as 37.32?and a long-range order structure might be involved around the T_g.Besides,the corrosion behaviors of the amorphous and crystalline Pd_40.5Ni_40.5P₁₉9 and Pd_77.5Cu₆Si_16.5 alloys in simulated seawater were investigated.It is found that the surface of both amorphous and crystalline Pd _40.5Ni_40.5P₁₉alloys is uniformly corroded without pitting.The corrosion resistance of the crystalline Pd_40.5Ni_40.5P₁₉ alloy is superior than that of the amorphous Pd_40.5Ni_40.5P₁₉ alloy due to the inert phosphides and noble palladium phases formed after crystallization.However,different-sized pitting holes are found on the surface of both amorphous and crystalline Pd_77.5Cu₆Si_16.5 alloys,and the amorphous Pd_77.5Cu₆Si_16.5 alloy shows better corrosion resistance than its crystalline counterpart.This phenomenon may be associated with Cu-rich phase on the surface of the crystalline Pd_77.5Cu₆Si_16.5 alloy,which promotes the nucleation of the pitting.