Effects Of Ion Irradiation On Aluminum Based Metallic Glasses

In this thesis, Al_92-xFe_xCe₈（x=0,2,5） metallic glassy ribbons have been preparedby melt-spinning technique. The irradiation tests have been carried out under170keVnitrogen ion or proton irradiation with total fluencies of5×10¹⁵,1×10¹⁶and2×10¹⁶cm^-2.The microstrcture, thermal stability, and mechanical properties of as-spun and irradiatedsamples have been examined by X-ray diffraction （XRD）, differential scanningcalorimeter （DSC）, transmission electron microscopy （TEM） and nano-identation. Theirradiation mechanism of metallic glasses has been investigated, experimentally andtheoretically.Firstly, the microstrcture and thermal stability of as-spun Al-based metallic glasseshave been characterized. In order to obtain the crystallization activation energies ofmetallic glasses studied, DSC tests were carried out at different heating rates. After Feaddition, the activation energy of Al-Ce-Fe metallic glasses increases. Upon heating, forthe case of Al₉₂Ce₈metallic glasses, Al₉₂Ce₈phase first precipitated and thendecomposed into f.c.c-Al phase and Al₄Ce phase. The change in Fe content leads to asignificant change in the crystal phases. Vickers Indentation can induce thecrystallization of Al-based metallic glass. After indentation tests, Al₉₂Ce₈, f.c.c-Al andAl₄Ce can precipitate from the Al₉₀Fe₂Ce₈glassy matrix.The collision between ion and target atom was calculated carefully. The resultshows nitrogen ion is able to pass more energy to target ion, compared by proton withthe same energy. As a result, more target atoms are knocked off its original sites undernitrogen ion irradiation. According to the calculation using SRIM code, the projectedrange of nitrogen ion and proton in Al-Fe-Ce metallic glasses is337nm and1482nm,respectively. What’s more, the irradiation damage coursed by nitrogen ion is two ordersof magnitude more than that coursed by proton.After irradiation, the surface roughness of Al-based metallic glasses reducessignificantly, due to the plastic flow of surface induced by ion irradiation. Meanwhile,the activation energy of crystallization decreases after irradiation. The XRD resultsshow that Al₉₂Ce₈, f.c.c-Al and Al₄Ce nano-crystals precipitated fromAl₉₂Ce₈metallicglasses after irradiation. The size of nanocrystalline ranged from10nm to50nm, and almost kept unchanged with increasing the irradiation dose. When the irradiation doseof N+was5×10¹⁵cm^-2, numerous Al₉₂Ce₈crystals formed from Al₉₂Ce₈amorphousmatrix. Only small amount of crystals precipitated in Al₉₀Fe₂Ce₈metallic glasseswhereas Al₈₇Fe₅Ce₈metallic glass remained amorphous structure after irradiation. Itsuggests that the metallic glass with high crystallization activation energy will exhibithigh resistance to crystallization during irradiation. Nnao-indentation tests indicate thatafter irradiation, the hardness of Al-based metallic glasses have enhanced hardnessvalues and lower plasticity.