Investigations of Structure and Glass Forming Abilty of Amorphous Alloys
|School||Harbin Institute of Technology|
|Course||Materials Processing Engineering|
|Keywords||amorphous alloys glass forming ability structure synchrotron radiation high energy X-ray diffraction|
The glass forming ability of Al92-xCe8Fex（x=16） ternary amorphous alloys are investigated in this dissertation combined with the concept of metallurgy. The amorphous structure of Zr53Cu18.7Ni12Al16.3, Zr51.9Cu23.3Ni10.5Al14.3 and Zr50.7Cu28Ni9Al12.3 are studied by using synchrotron radiation high energy X-ray diffraction （HRXRD） and the efficient close packing model proposed by D.B. Miracle.The ribbons of the six Al92-xCe8Fex（x=16） ternary alloys all exhibit amorphous natures when the thickness is 3050μm. A pre-peak at about 17°of 2θon the conventional X-ray diffraction （XRD） pattern implies the medium range order in each alloy. Moreover, in the XRD pattern of Al86Ce8Fe6, the diffuse halo splits into two subtle sub-peaks which indicate different correlations in this alloy. When the thickness increases to 5070μm, crystalline phases appear in the amorphous matrix. Among these crystallites, the majority are silicates and oxides which are attributed to the inappropriate processing. Besides these, there still exist some competing crystalline phases such as Fe2Al5 and Al13Fe4.Differential thermal analyzer （DTA） curve for each of the six Al92-xCe8Fex（x=16） ternary alloys displays only one fusion peak which demonstrates the six alloys all exist near the eutectic. Gibbs free energy difference ?G between supercooled liquid and crystalline phase are calculated according to the formula by Battezzati and Garrone. It appears that in the six alloys ?G decreases with increasing the Fe component at the same temperature. However, the differences among the six alloys are relatively small.Reduced pair distribution functions （PDFs）, G（r）, for Zr53Cu18.7Ni12Al16.3, Zr51.9Cu23.3Ni10.5Al14.3 and Zr50.7Cu28Ni9Al12.3, obtained by HRXRD are very similar. The first peak for each of the three alloys splits into two sub-peaks. It is interesting that the two sub-peaks for the three alloys evolve in different trends. Atomic weight factor and bond length for each atomic pairs in this Zr-Cu-Ni-Al imply that, on the PDF curve the former sub-peak is mainly attributed by Al-Cu atomic pair, but the latter one is attributed by Zr-Zr pair. The increasing pairs of Al-Cu and decreasing pairs Zr-Zr are corresponding to the evolution of the former and latter sub-peaks respectively.Based on the efficient close packing model proposed by D.B. Miracle, the structures for the three Zr53Cu18.7Ni12Al16.3, Zr51.9Cu23.3Ni10.5Al14.3 and Zr50.7Cu28Ni9Al12.3 alloys are constructed. We consider the substitution of small atoms Cu for large atoms Zr in this alloy Zr50.7Cu28Ni9Al12.3 stabilize the efficient close packing structure, which further improve the glass forming ability of this alloy.