Oxidation behavior of Cu 60 Zr 30 Ti 10 bulk metallic glass
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The oxidation kinetics of Cu60Zr30Ti10 bulk metallic glass and its crystalline counterpart were studied in oxygen environment over the temperature range of 573–773 K. The oxidation kinetics, measured with thermogravimetric analysis, of the metallic glass follows a linear rate law between 573 and 653 K and a parabolic rate law between 673 and 733 K. It was also found that the oxidation activation energy of metallic glass is lower than that of its crystalline counterpart. The x-ray diffraction pattern showed that the oxide layer is composed of Cu2O, CuO, ZrO2, and metallic Cu. Cu enrichment on the topmost oxide layer of the metallic glass oxidized at 573 K was revealed by x-ray photoelectron spectroscopy while there was a decrease in Cu content in the innermost oxide layer. The oxide surface morphologies observed from scanning electron microscopy showed that ZrO2 granules formed at low temperatures while whiskerlike copper oxides formed at higher temperatures.
I. INTRODUCTION
Bulk metallic glasses are being developed for structural applications due to their excellent mechanical properties, wear properties, and corrosion resistance. Recent works reported that Cu-based bulk metallic glasses with high tensile strength of over 2000 MPa can be prepared by copper mold casting.1,2 For instance, optical machinery and cutting tools can be made to take advantage of their superior mechanical properties.3 However, when metallic glasses are subjected to a relatively high temperature for a long period of time, oxidation occurs and deteriorates their performance. Several studies have been performed on the oxidation behavior of metallic glass ribbons,4–10 but limited results are available on bulk metallic glasses.11–13 Numerous studies have been performed on the oxidation behavior of metallic glasses, but the results are still controversial. Previous studies reported that the oxidation resistances of metallic glass are superior to those of its crystallized state.6,7 On the other hand, a number of reports showed that the metallic glass has a higher oxidation rate than that of the annealed state.8–10 Besides, earlier investigations14–16 found that copper segregation occurs after oxidation of Cu–Zr metallic glasses but it does not happen in other Cu-containing metallic glasses such as Zr–Cu–Al–Ni alloys.13,17 The present study was focused on the oxidation kinetics and the nature of the a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2005.0182 1396
http://journals.cambridge.org
J. Mater. Res., Vol. 20, No. 6, Jun 2005 Downloaded: 27 Feb 2015
oxide formation of both as-cast and crystallized Cu60Zr30Ti10 bulk metallic glasses. II. EXPERIMENTAL PROCEDURE
A Cu60Zr30Ti10 (nominal composition) bulk metallic glass sample (referred to as CZT in this article) was prepared by arc melting the mixtures of pure Cu, Zr, and Ti metals in a Ti-gettered argon atmosphere. Bulk metallic glass rods with 3-mm diameters were then prepared by suction casting into a copper mold. The crystalline sample (referr
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