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Zrnbcunial Bulk Amorphous Alloy Crystallization Behavior And Performance

Posted on:2004-03-24Degree:MasterType:Thesis
Country:ChinaCandidate:X F LiFull Text:PDF
GTID:2191360092981811Subject:Materials science
Abstract/Summary:PDF Full Text Request
In this paper, Zr57Nbi5_xCu15.4Nii2.6Alx bulk amorphous alloys were prepared by means of copper-mold vacuum suction casting and the glass forming ability(GFA) and structure were investigated by differential scanning calorimeter(DSC), X-ray diffraction(XRD), scanning electron microscope(SEM), etc. Differential scanning calorimeter was used to study crystallization kinetics of Zr57Nb5Cu15.4Ni12.6Al10 bulk amorphous alloy by Kissinger and Ozawa equation under non-isothermal conditions and Johnson-Mehl-Avram model under isothermal conditions, respectively. The crystallization process of Zr57Nb5Cu15.4Ni12.6Al10bulk amorphous alloy has been also studied systematically. Moreover, mechanical properties of Zr57Nb5Cu15.4Ni12.6Al10 bulk amorphous alloy have been discussed profoundly. The following results have been obtained:(1) Zr57Nb5Cu15.4Ni12.6Al10 bulk amorphous alloy has larger glass forming ability(GFA) and a wider supercooled liquid region. The glass transition temperature(Tg), the onset crystallization temperature(Tx) and the supercooled liquid region defined by the difference between Tx and Tg are about 697.5K, 747.4K and 50K respectively.(2) Significant kinetic effect has been found in the glass transition temperature, the onset crystallization temperature and the crystallization peak temperature.(3) Apparent activation energy of crystallization of Zr57Nb5Cu15.4Ni12.6Al10 bulk amorphous alloy has been obtained with Kissinger and Ozawa equation, the apparent activation of crystallization of the first stage is 320.4kJ/mol and 332.7kJ/mol and that of crystallization of the second stage is 324.3 kJ/mol and 336.8 kJ/mol respectively. The avrami exponential of crystallization, n, is about 1.60, which implies the process of crystallization is under control of diffusion process. The whole process of crystallization for Zr57Nb5Cu15.4Ni12.6Al10 bulk amorphous alloy may be considered as: amorphous - amorphous( a and 3 ) - amorphous( a and P )+NiZr2+unknown-n-phases-amorphous(a and 3 )+NiZr2+ Zr2Cu-NiZr2+Zr2Cu+unknown phases(4) The compressive fracture strength of Zr57Nb5Cu15.4Ni12.6Al10 bulk amorphous alloy reaches 1705MPa, Compression ratio is only 0.104, fracture surface morphology takes on uniformly distributed veinal pattern. Fracture strength decreases obviously with the increase of annealing temperature and the mechanism of fracture changes form ductile fracture to brittle fracture.(5) Microhardness of Zr57Nb5Cu15.4Ni12.6Al10 bulk amorphous alloy is about 462Hvo.2, which depends on the annealing temperature and holding time. The microhardness shows a tendedcy to increase evidently, then falls slightly with the two annealing parameters.(6) In 3%NaCl, 10%HC1 and 10%NaOH water solution, the corrosion resistance of Zr57Nb5Cu15.4Ni]2.6Al]o bulk amorphous alloy is best in 3%NaCl solution and rather bad in 10%NaOH solution.
Keywords/Search Tags:Bulk amorphous alloy, Kinetics of crystallization, Crystallization behavior, Mechanical property, Corrosion behavior
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