Study On Composition Design, Formation And Stability Of Uranium Iron-based Amorphous Alloys

Due to the excellent properties,amorphous alloys have become a promising application of a new generation of metal materials and a hot topic in advanced materials research.However,U-based amorphous alloy research is very scarce.The study of U-based amorphous alloys is expected to deepen the understanding of the formation mechanism of amorphous materials and promote the development of amorphous theory,which has important scientific significance.In this paper,the "Cluster + Connected atoms" model,"Deep eutectic point theory",and"Inoue three principles" and other empirical criteria are used for alloy composition design.U-Fe-based amorphous alloys were prepared by melt-spinning method.By adding Al and Sn elements,U-Fe-Sn and U-Fe-Al ternary amorphous alloys were successfully obtained.XRD and DSC results show that it has strong amorphous forming ability and thermal stability,and the glass transition temperature(Tg)characteristics are observed in the DSC curves.The reduced glass transition temperature(Trg)of several amorphous alloys are more than 0.6.It is found that several physical parameters have great impact on the formation ability of uranium-based amorphous alloys,including the atomic size of the alloy components,the electronegativity,the electron concentration and the mixing enthalpy.The main mechanism is to change the stability of the alloy liquid from both the local atomic structure and the electronic structure.The study of the crystallization behavior of U62Fe28Al10 alloy is helpful to understand the formation mechanism and the origin of thermal stability in U-based amorphous alloy.The non-isothermal crystallization behavior of U62Fe2sAl10 was investigated by using DSC.Basic thermodynamic parameters such as glass transition temperature(Tg),crystallization temperature(Tx)and crystallization peak temperature(Tp)were obtained at different heating rates.Its kinetic fragility parameter,overall crystallization activation energy and Kauzmann temperature were determined to be 24,262 kJ/mol,and 486 K,respectively.The evolution of the crystallization activation energy with the volume fraction crystallized,which was established by both the Kissinger and Ozawa methods independently,suggests a typical three-staged process for the crystallization.As reflected by the change of the local Avrami exponent with the fraction crystallized,nucleation dominates the whole process.This work is helpful for understanding the formation and thermal stability of U-based amorphous alloys,and also for the development of new materials of this kind.U-based amorphous alloys,as a new kind of potential materials,would be used in the nuclear industry,their mechanical properties still poorly understood.Especially,creep properties of these materials have not been reported in the previous studies.In order to preliminarily investigate the creep phenomenon derived from stress reaction;the ambient creep behavior of a new amorphous alloy U65Fe30l5 was conducted.This alloy was tested by using a nano-indentation technique under different peak loads and loading rates.Nano-indentation experiments show that U65Fe30Al5 amorphous alloy has excellent mechanical properties,the elastic modulus of about 90GPa.The hardness is about 6.0GPa,which is significantly higher than that of the traditional uranium alloy(?3GPa).The results indicate that the creep displacement gradually increases with either the peak load or the loading rate in equal creeping time,but this tendency vanishes when exceeding a critical loading rate.The fitting based on an empirical creep equation reveals that the stress exponent of the alloy ascends when raising the peak load,and firstly declines with the loading rate and then remains constant above the critical rate.Compared with conventional crystalline alloys,the stress exponent of the U-Co-Al alloy is larger,reflecting the possible existence of rich free volume in the amorphous alloy.