Effects of alloying on oxidation of Cu-based bulk metallic glasses
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The oxidation kinetics and the effects of alloying on the oxidation behaviors of copper-based bulk metallic glasses were studied. The oxidation kinetics, oxide compositions, and structures were investigated by thermogravimetric analysis (TGA), x-ray diffraction, x-ray photoelectron spectroscopy (XPS), and scanning electron microscopy. Both the TGA results and the XPS depth profile measurements showed that the oxidation resistance of Cu60Zr30Ti10 bulk metallic glass was improved by adding Hf, but it deteriorated when it was alloyed with Y. The oxide phases were found to be ZrO2, Cu2O, and CuO in samples heated at 573 K while an additional metallic Cu phase was detected in the ones heated at 773 K. A porous oxide structure was observed in the (Cu0.6Zr0.3Ti0.1)98Y2 metallic glass oxidized at 673 K, and the poor oxidation resistance of the alloy is attributed to the porous structure.
I. INTRODUCTION
In recent years, Cu-based bulk metallic glasses have been developed in Cu–Zr–Ti,1 Cu–Hf–Ti,2 and Cu–Zr– Hf–Ti3 alloy systems. Extensive investigations have been done on the mechanical properties1–5 and crystallization behaviors6–10 of these glassy alloys. The Cu-based bulk metallic glasses (BMGs) exhibit high tensile strength exceeding 2000 MPa and good thermal stability against crystallization. However, only a limited number of reports can be found on the corrosion behaviors of the Cubased metallic glasses in aqueous environment,11–14 and there has been no such investigation concerning oxidation in gaseous environments. Some of the applications of metallic glass such as transformer core and heat exchanger require that the materials be used at elevated temperatures in air, and their performance might be affected by oxidation. On the other hand, BMGs can achieve near-net-shape formation by superplastic forming at temperatures in the supercooled liquid region. Better understanding of the oxidation behaviors of metallic glass can therefore enhance the potential for applications of this family of materials. The oxidation kinetics and oxide structures of metallic glasses were mainly studied with thermogravimetric analysis (TGA) and x-ray diffraction (XRD), respectively.15–19 The oxidation processes of some Zr-based metallic glasses were usually found to follow the parabolic rate law which implies a diffusion controlled
II. EXPERIMENTAL PROCEDURE
a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2005.0336
Three Cu-based alloys with nominal compositions Cu60Zr30Ti10, Cu60Zr20Hf10Ti10, and (Cu0.6Zr0.3Ti0.1)98Y2
J. Mater. Res., Vol. 20, No. 10, Oct 2005
http://journals.cambridge.org
process. The major oxide phase was identified as ZrO2, possibly due to the high chemical affinity of Zr with oxygen. On the other hand, Sun et al.20 reported that a Ni-rich phase was observed on the alloy–oxide interface, and they suggested that the growth of the oxide might be controlled by Ni back-diffusion. Some other researchers investigated the oxidation mechanism using surfaceanalysis techniques21
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