Crystallization Behavior Of Zr-based Bulk Amorphous Alloys

In this thesis, crystallization behavior of Zr₆₀Al₁₅Ni₂₅, Zr55Al10Ni5Cu30,Zr₆₅Al₁₀Ni₁₀Cu₁₅ and Zr_52.5Al₁₀Ni₁₀Cu₁₅Be_12.5 amorphous alloys have been systematically investigated by XRD and DSC.In this first part of the thesis, a historic progress of bulk amorphous alloys has been critically overviewed, and narrate the excellent properties and production methods of amorphous alloy shortly, lastly introduce crystallization approach, crystallization types, crystallization thermodynamics and crystallization kinetics particularly.Different scanning calorimeter (DSC) was used to investigate non-crystallization kinetics of Zr₆₀Al₁₅Ni₂₅,Zr55Al10Ni5Cu30 and Zr₆₅Al₁₀Ni₁₀Cu₁₅ amorphous alloys, the results show that glass formation ability and crystallization of amorphous alloys also relate to heating rate, and it had a dynamic effect. Kissinger equation and Ozawa equation were used to calculate the activation crystallization energy(Eg,Ex and Ep), resulting in a small deviation between them, and Eg of the alloys are higher than Ex and Ep. In isothermal condition, JMA equation was used to calculate the activation energy (Ec) of amorphous alloy, the results show that addition of Cu can improve the thermal stability of the Zr-based alloy, and addition of 15at% Cu is more availability than addition of 30at% Cu. In addition, the values of Avrami exponent which also obtained by JMA equation show that the crystallization of Zr₆₀Al₁₅Ni₂₅ is polymorphic crystals with a decreasing nucleation rate for the former and controlled by the interface, and crystallization of Zr55Al10Ni5Cu30 and Zr₆₅Al₁₀Ni₁₀Cu₁₅ are similar, with a decreasing nucleation rate for the former and controlled by the volume diffusion. Different scanning calorimeter (DSC) was used to investigate crystallization kinetics of Zr_52.5Al₁₀Ni₁₀Cu₁₅Be_12.5 amorphous alloy, which can in contrast with crystallization of Zr₆₅Al₁₀Ni₁₀Cu₁₅. The result shows that the thermal stability of Zr_52.5Al₁₀Ni₁₀Cu₁₅Be_12.5 alloy is higher than Zr₆₅Al₁₀Ni₁₀Cu₁₅, and the addition of Be element can improve the thermal stability of the Zr-based alloy, which also can be made firm by anneal experiment.X-ray diffraction was used to investigate crystallization of Zr₆₅Al₁₀Ni₁₀Cu₁₅ and Zr_52.5Al₁₀Ni₁₀Cu₁₅Be_12.5 alloy. The results show that Zr₆₅Al₁₀Ni₁₀Cu₁₅ amorphous alloy was annealed at different conditions, metastable phase Zr₂Ni and other Zr-Al,Zr-Cu compounds were precipitated in the amorphous matrix first, and the crystallized phases Zr₂Cu,Zr₂Al₃ and other compounds were produced later; Zr_52.5Al₁₀Ni₁₀Cu₁₅Be_12.5 amorphous alloy was annealed at different conditions, ZrCu,ZrBe₂,Zr₂Al₃ main crystallized phases were precipitated in the amorphous matrix. With the addition of Be element, the Zr-Ni metastable compound is inhibited precipitating. Integrated them with results of crystallization kinetics, it indicates that the crystallization of Zr₆₅Al₁₀Ni₁₀Cu₁₅ and Zr_52.5Al₁₀Ni₁₀Cu₁₅Be_12.5 is also with a decreasing nucleation rate for the former and controlled by the volume diffusion, but crystallization types is different, and Zr₆₅Al₁₀Ni₁₀Cu₁₅ is the initial crystallization process, and the crystallization of Zr_52.5Al₁₀Ni₁₀Cu₁₅Be_12.5 alloy is eutectic type. The addition of Beryllium influences nucleation and growth of crystallization of amorphous alloy, and lead to the transition of crystallization type.