Abstract
Two CuZr alloys, Cu-50 at% Zr and Cu-54 at% Zr, were splat quenched to the non-crystalline state using a piston and anvil device. The glass transition and crystallization temperatures, as well as the enthalpy releases observed during crystallization were measured using differential scanning calorimetry of as-splat specimens and specimens aged below T g. Transmission electron microscopy and X-ray diffraction experiments were utilized to monitor phase and structural changes in the alloys as they were transformed to the crystalline state. The results of the investigation indicated that the non-crystalline to crystalline transformation of these two alloys in constant heating rate experiments above T g was a two-step process. The initial step, which is associated with a large exothermic reaction, results in the appearance of crystallites in a matrix of non-crystalline material. The final step, associated with a smaller exothermic reaction, results in the total transformation of glass to the crystalline state and the formation of the equilibium crystalline phases. The effect of aging these splat-quenched non-crystalline alloys at temperatures below T g was also investigated. It was determined from these experiments that crystallization does occur when the non-crystalline alloys are aged ∼ 15°C below T g. However, the incubation time for crystalline nucleus formation was found to be substantially greater for the Cu 50Zr 50 glass. Finally, it was determined that the thermal stability of the aged glass relative to the spontaneous crystallization observed during the constant heating rate experiments above T g decreases as a function of aging time.
Published Version
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