| Pacific Rim Symposium on Surfaces, Coatings and Interfaces (PacSurf 2018) | |
| Nanomaterials | Tuesday Sessions |
| Session NM-TuM |
| Session: | Nanofabrication and Nanodevices |
| Presenter: | Zhongqiu Cao, Shenyang Normal University, China |
| Authors: | Z.Q. Cao, Shenyang Normal University, China X.T. Yin, Shenyang Normal University, China Q,Y. Tian, Shenyang Normal University, China Y. Wang, Shenyang Normal University, China K. Zhang, Shenyang Normal University, China J. Lu, Shenyang Normal University, China |
| Correspondent: | Click to Email |
In this paper, two bulk nanocrystalline LPRAg-25Cu and MAAg-25Cu (at.%) alloys were prepared by liquid phase reduction and mechanical alloying methods, respectively, and afterwards hot pressing process. Fig. 1 depicts the X-ray diffraction (XRD) pattern (a) and the transmission electron microscopy (TEM) photograph (b) of LPRAg-25Cu alloyed powders. These alloyed powders have no impurities with about 10 nm average grain sizes. The densities of two bulk nanocrystalline Ag-25Cu alloys exceed 99%. The average grain size measured by XRD is about 13 nm after liquid phase reduction and about 27 nm after hot pressing, about 8 nm after mechanical alloying and about 19 nm after hot pressing.
Fig. 2 depicts the microstructures of two nanocrystalline alloys and a coarse grained counterpart (PMAg-25Cu). They all are composed of two phases. One is α phase rich in Ag, the other is β phase rich in Cu. The microstructure of coarse grained PMAg-25Cu alloy is extremely inhomogeneous. The microstructure of nanocrystalline LPR or MAAg-25Cu alloys is more homogeneous than that of coarse grained PMAg-25Cu alloy, while the microstructure of nanocrystalline LPRAg-25Cu alloy is most homogeneous.
Fig. 3 depicts Open Circuit potential (a), polarization (b), EIS (c), and Mott-Schottky (d) curves of three Ag-25Cu alloys. Corrosion rates of three Ag-25Cu alloys increase in the range of PMAg-25Cu, MAAg-25Cu and LPRAg-25Cu alloys. The corrosion rate of nanocrystalline alloy is faster than that of corresponding coarse grained alloy. The faster corrosion rates are attributed to the different microstructures of three Ag-25Cu alloys prepared by the different processes including the grain size as well as phase distribution and compositions. EIS plot of coarse grained PMAg-25Cu alloy is composed of a single capacitive loop. The corrosion process is controlled by electrochemical reactions. EIS plots of nanocrystalline MAg-25Cu and LPRAg-25Cu alloy are composed of a single capacitive loop with diffusion tail. The corrosion processes of two nanocrystalline Ag-25Cu alloys are controlled by diffusion. The passive films formed on three Ag-25Cu alloy surface exhibit n-type semiconducting properties. The passive current density of LPRAg-25Cu alloy is lower than that of PMAg-25Cu alloy, but higher that of MAAg-25Cu alloy. Thus, the chemical stability of passive films on MAAg-25Cu alloy surface is highest.
Acknowledgements
This work is financially supported by the National Natural Science Foundation of China (NSFC) under contracts Nos. 51271127 and 51501118, Liaoning Natural Science Foundation of China under contract No. 201602679.