Thermal Stability of Zr-Based Glassy Alloys Examined by Electrical Resistance Measurement

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Abstract
The effects of the thermal histories during the sample preparation and in measuring the physical properties on thermal stabilities of glassy Zr60Al15Ni25 and Zr60Al15Ni7.5Co2.5Cu15 alloys were examined mainly by the electrical resistance measurement. As long as the present experiments are concerned, the glass transition and crystallization temperature were not significantly affected by the thermal histories as for as-quenched samples. The temperature derivative of the electrical resistance dR⁄dT exhibited a negative value below the glass transition temperature. In the contrast, dR⁄dT was turned to a positive value in the supercooled liquid region. Although dR⁄dT showed an almost constant value for glassy Zr60Al15Ni25 alloy, an apparent two step change was observed for glassy Zr60Al15Ni7.5Co2.5Cu15 alloy in the supercooled liquid region. It was found out that the dR⁄dT in the supercooled liquid region was significantly affected by the thermal history, especially the atmosphere in measuring the electrical resistance. Even for the sample where the oxide layer of the surface was taken away by mechanical polishing and the resistance measurement was carried out in the vacuum, the dR⁄dT retained a small positive value in the supercooled liquid region.