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Welding Journal | January 2014

A B Under pure oxygen atmosphere, Ag ⎡⎣⎢ Oxygen solubility in liquid silver in air at 1250 K equals 10.5 sm3/g Ag under pure oxygen atmosphere. It will be 2.2 times higher. Analysis of the BaTiO3/Ag-Cu-O alloy interface shows the presence of a transitive black zone ~7–10 μm thick, which is an obvious result of copper diffusion into the ceramic substrate in air media (Fig. 11). But in oxygen atmosphere such zone is thin (~ 1 μm) or absent (Fig. 12). It is important for saving whole degree ferroelectric properties of such ceramics. Brazing of Ferroelectric Barium Titanate Under the air, and especially under pure oxygen atmosphere, the process of joining (brazing) of ferroelectric BaTiO3 ceramics can be performed. Braze alloy Ag-10 Cu was used for joining BTO ceramics in air and Ag-3 Cu under pure oxygen atmosphere. The samples of the perovskite ceramics brazed with Ag-Cu-O alloy were obtained. The shear strength of ceramic/ceramic butt joints was measured (Fig. 13, Table 2). It was shown that the strength of brazed samples was 46 MPa. It is 88% of the average strength of monolithic ceramics, which is more than two times the strength given in the literature for perovskite materials brazing. The metal that can be joined to ferroelectric BTO is a noble one — platinum (wire electrodes, plates). The pure Ag can be used as well with minimal difficulty, accounting that the melt temperature for Ag- Cu-O alloys were some lower than for pure Ag. As it was shown practically, platinum provides a strong homogeneous brazed joint that can also be used for brazing ferroelectric ceramics to construction metal. The brazed and metalized ferroelectric barium titanate samples were obtained using plastic In-Ti filler alloy in vacuum at 720 K. It was possibly because such ceramic begins to lose oxygen and ferroelectric properties in vacuum at heating above 900 K. Conclusion Transitive zone A combined investigation including contact interaction and wetting of BaTiO3 perovskite ceramics by liquid metals was carried out. Two states of barium titanate were studied. For semiconducting BaTiO3-x with an oxygen defect, experiments in vacuum for 13 pure metals and Ti-containing alloys (Cu- Sn-Ti, Cu-Ga-Ti, and Ag-Cu-Ti) were carried out. Most of the metals under investigation do not wet BaTiO3. Titanium addition sharply increases capillary properties and adhesion. Compositions of capillary active braze alloys, plus methods in brazing and metalization BaTiO3 for high contact strength achieving, were found. The brazing process for ferroelectric barium titanate must be carried out in the oxygen-containing environment — in air or preferably pure oxygen. For brazing and metalization of ferroelectric, ceramic BaTiO3 used Ag-Cu-O alloys. Based on obtained data, metal-oxygen technologies of metalization and brazing BaTiO3 ceramics in air and pure oxygen atmosphere were developed, and also a method of metalization with high adhesion using metal melts containing oxygen. The plastic In-Ti alloy was tested for metalization and brazing in a vacuum of perovskite ceramics. It can be used for the semiconductor BaTiO3 ceramics at 970 K and ferroelectric BaTiO3 ceramics at 720 K, allowing use of the full range of unique electrical properties for perovskite materials. Acknowledgments The authors wish to thank Prof. M. D. Glinchuk and PhD E. P. Garmash for synthesis of ceramic samples; PhD O. V. Durov for assistance in the brazing processes; and Prof. S. A. Firstov and Dr. M. V. Karpets for microstructure interface investigations. References 1. Xu, Y. 1991. Ferroelectric Materials and Their Applications. North-Holland, Amsterdam. 2. Uchino, K. 1997. Piezoelectric Actuators and Ultrasonic Motors. Norwell, Mass., Kluwer. 3. Bhattacharya, K., and Ravichandran, G. 2003. Ferroelectric perovskites for electromechanical actuation. Acta. Mater. 51: 5941–5960. 4. Scott, J. F. 2000. Ferroelectric Memories. Springer Verlag, Berlin. 5. Ramesh, R. 1997. Thin Film Ferroelectric Materials and Devices. Kluwer. Academic, Norwell, Mass. 6. Fernie, J. A., and Ironside, K. I. 1999. Ceramic brazing. Materials World 7(11): 686–688. 7. Bursian, E. V. 1974. Nonlinear Crystal (barium titanate). Nauka, Moskow. 8. Brillson, L. J. 1994. Metal-semiconductor interface. Surf. Sci. 229/230: 909–927. 9. Wang, S.-F., Yang, T. C. K., and Lee, S.-C. 2001. Wettability of electrode metals on barium titanate substrate. J. Mater. Sci. 36: 825–829. 10. Cann, D. P., Maria, J.-P., and Randall, C. A. 2001. Relationship between wetting and electrical contact properties of pure metals and alloys on semiconducting barium titanate ceramics. J. Mater. Sci. 36: 4969–4976. 11. Lee, C. Y., Dupcux, M., and Tuan, W. H. 2006. Adhesion strength of Ag/BaTiO3 interface. Scripta Mater. 54(3): 453–457. O k pure oxygen ⎤⎦⎥ = 1 (4) WELDING JOURNAL 13-s WELDING RESEARCH Fig. 12 — Cross section of Ag-Cu-O drop (top part) on surface of the ferroelectric BaTiO3. A — In air; B — in oxygen. Fig. 13 — The Weibull’s graph of shear strength for brazed in air ferroelectric BaTiO3 ceramics samples.


Welding Journal | January 2014
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