The roles of chemical composition on corrosion and mechanical properties of binary Zr-Cu metallic glass thin films

摘要

One of the amorphous alloy materials - metallic glass thin films (MGTFs) has its advantage of designing chemical composition without restricting the glass formation ability. It was previously reported that the Zr-Cu MGTFs prepared by magnetron co-sputtering exhibit an amorphous state within the 10 - 90 at.% Cu compositional range. However, a systematic investigation on the corrosion mechanism and kinetics of Zr-Cu MGTFs in sulfuric acid solution or even Zr-based MGTFs in a wide compositional range is still lacking in the literature. Zr_(100-x)Cu_x MGTFs (x=27.5, 47.5, 79, 90 at. %) were successfully prepared for finishing application and selected to probe into the role of the chemical composition on corrosion behavior and mechanical proprieties of Zr-Cu MGTF binary system. It was investigated by electrochemical methods, SEM, EDS, XPS and mechanical tests with nanoindenter. The Zr-Cu MGTFs display typical amorphous structure, but the Zr-90 at. % Cu thin films exhibits partial crystallization composed of Cu or Cu_(51)Zr_(14) phase. The Zr-Cu MGTFs have different corrosion resistance and corroded surface morphologies with respect to copper content. The corrosion current density increase and EIS impedance of Zr-Cu MGTFs decrease by increasing the copper content in films. The main chemical component of passive oxide layer on MGTFs is ZrO_2 oxide, while for samples with higher copper content some Cu and CuO species were identified by XPS. The ZrO_2 formed on the surface benefits to passivation but the corrosion resistance of MGTFs depends on passive film coverage. The Zr-27.5 at. % Cu MGTF has the best corrosion resistance, and displays stable passivation with a very large polarization potential range. As the copper content increases in the Zr-Cu matrix, the Young's modulus follows a linear evolution from about 86 GPa for Zr-27.5 at.% Cu to 120 GPa for Zr-90 at.% Cu sample, respectively. The hardness increases from about 5 GPa for Zr-27.5 at.%Cu sample to the maximum value of 6.7 GPa for the Zr-79 at.% Cu sample. The best relative proportion of Zr and Cu elements in the Zr-Cu MGTFs can be designed to have the balance between corrosion resistance and mechanical properties. The evolution of free volume affects mechanical properties, and it is related to the corrosion behavior of Zr-Cu MGTFs. The reducing of free volume can benefit the maintaining of corrosion resistance is true but may be secondary to the chemical composition of amorphous alloy.