The Preparation And Glass Forming Ability Of Zr-Cu-Al Metallic Glasses Under Argon And Hydrogen Mixed Atmosphere

Bulk metallic glasses?BMGs?,possessing a series of superior properties,as for instance high strengths,large elastic strain limits,good corrosion resistance as well as excellent soft magnetism,have attracted tremendous attention by experts and scholars in various fields,because of their potential applications in the fields of aerospace,machinery,chemical engineering,and etc.In this thesis,two typical metallic glasses of Zr₆₄Cu₂₄Al₁₂and Zr₆₆Cu₂₂Al₁₂ were prepared by argon-hydrogen plasma arc melting method,through which the temperature field was changed and that had led to the effect of hydrogen microalloying.The increasing regularity and mechanism of the glass-forming ability?GFA?for Zr-based metallic glasses were studied systematically in the present work.The temperature field in the melting process of Zr-based metallic glasses were simulated,and results showed that,the temperature field distribution varied significantly with the addition of hydrogen,where a typical linear relationship existed between the melt temperature and the hydrogen content in a H₂/Ar mixed atmosphere.The melt temperature would reach its maximum when the hydrogen addition increased up to 10%,and at the same time,the shell thickness was the thinnest,resulting in the largest thermal efficiency.The hydrogen content remained in the casting samples was measured,which was coincide with the theoretical value calculated by applying the Sieverts'Law,and it was found that a maximum content,over 200 ppm,was existed in the sample prepared under an atmosphere with 10%of hydrogen addition.The structural analysis of Zr₆₄Cu₂₄Al₁₂ and Zr₆₆Cu₂₂Al₁₂BMGs under different atmospheres showed that the addition of hydrogen induced the increase of critical section size of the BMGs,and the critical section size reached the maximum value with the addition of 10%hydrogen,resulting in a fully amorphous structure in the sample as casted.The thermal properties of Zr-based metallic glasses were analyzed via differential scanning calorimetry?DSC?,and it was found that the undercooled liquid range?T_x,the K criterion as well as the reduced glass transition temperature T_rg were significantly increased in the alloy samples after casted with hydrogen addition.In addition,it showed that,with hydrogen addition,the Zr-based metallic glasses had a larger crystallization activation energy and a smaller fragile parameter,leading to an increase of the GFA in the hydrogen-induced Zr-based metallic glasses,according to the thermodynamics and dynamic analysis.The effects of hydrogen on the microscopic electronic structure of Zr-based metallic glasses were studied by X-ray photoelectron spectroscopy,and it was found that the internal shell electron confinement energy of the metal elements reached its minimum under the hydrogen content of 10%,indicating the formation of a compact packed structure,as well as the most numerous amount of the chemical bonds,enlarging the difficulty of long-range atomic diffusion and crystal nuclei.The research on the electronic structure of the shell of the valence shell showed that alloy possesses the strongest valence binding energy can be achieved in alloy casted under atmosphere with 10%of hydrogen content,where the atomic stacking structure was densest and the atomic cluster size was the smallest.It also indicated that simultaneously,the work function of the alloy had got its highest value,as well as the intensity of electron spectroscopy at the Fermi level reached its minimum,these revealing the decrease of the free energy and thus the stability of the alloy structure,and as a result of which the GFA of BMGs was thus improved under the condition.