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Zr-based Bulk Amorphous Alloy Relaxation And Crystallization Process

Posted on:2003-04-20Degree:MasterType:Thesis
Country:ChinaCandidate:X LiFull Text:PDF
GTID:2191360065956023Subject:Materials science
Abstract/Summary:PDF Full Text Request
Bulk amorphous alloys have many excellent mechanical properties such as high strength, wear resistance, corrosion resistance and soft magnetization. So, they have bright future with the applications in electronic, mechanical and chemical fields. Recently, many researches are focused on preparing bulk amorphous alloys. Amorphous alloys will loss many good properties after crystallization. However, partly crystallization of alloys will gain some useful microstructures. The relaxation process will influence the glass transition and crystallization of amorphous alloys in some sense. In this paper, the processes of relaxation and crystallization of amorphous alloys are investigated in order to help prepare bulk amorphous alloys.Zr-AI-Ni-Cu based alloys are chosen as the experimental alloys because of their strong ability to form amorphous alloys and their thermal stability. The relaxation and crystallization processes of bulk amorphous alloys are studied by dynamic mechanical analyzer (DMA), differential scanning calorimetry (DSC), X-ray diffraction (XRD) and transmission electron microscopy (TEM). In the paper, the influence of the relaxation process on the stability of amorphous alloys at a temperature lower than Tg is studied. The experimental results show that: continually heated, the activation energy for the glass transition of relaxed ZreaAlsNhsCuir is higher than that of as-quenched one. And, heated at a fixed temperature, the incubation time of relaxed Zr62AI8Nii3Cui7 is longer than that of as-quenched one. Therefore, a conclusion could be drawn that, at this time, the relaxation process here restrains the crystallization of the amorphous alloys. Moreover, the influence of the dynamic load on the crystallization is studied,the experimental results show that the applied dynamic load shortens the incubation time and accelerates the crystallization process of amorphous alloys. In the paper, the advantages and disadvantages of DMA and DSC are also compared; the results show that DMA is more sensitive than DSC for measuring phase transformations. In addition, the influence of the frequency and quantity of the dynamic load on the relaxation and crystallization process of amorphous alloys is studied;the results show that the storage modulus of Zr62AI8Nii3Cui7 amorphous alloys decreases with the decreasing of the frequency;the drop of the frequency accelerates the crystallization process;the frequency and quantity of the dynamic load influences the shape and size of the grains.
Keywords/Search Tags:Bulk Amorphous Alloys, Relaxation, Crystallization, Dynamic Mechanical Analyses, Differential Scanning Calorimetry
PDF Full Text Request
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