Brazing of zirconia with AgCuTi and SnAgTi active filler metals
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I. INTRODUCTION
BECAUSE of their special properties such as the ability to bear high temperatures, wear, and corrosion, fine ceramics have a significant potential for many structural and electrical applications. However, in many cases, the different ceramic parts must be connected by ceramic/ceramic joining technologies in order to fabricate complicated shapes or larger sizes. Additionally, other properties of ceramics (such as conductivity and toughness) are not comparable to those of metals. In such cases, ceramics may be joined to metals to obtain useful and stable components. As a result, the ceramic/ ceramic and ceramic/metal joining technologies will be critical for the structural application of fine ceramics in the future. In general, ceramic/ceramic and ceramic/metal joining have, so far, been accomplished by using a metal interlayer either by brazing or diffusion bonding. Brazing is a convenient way to get a good joint. However, in either ceramic/ceramic or ceramic/metal joining, the poor wettability of conventional filler metals on ceramics is the critical problem in using the brazing method.[1,2] To improve wettability, active elements such as titanium, zirconium, or hafnium are added to conventional filler metals, due to the chemical affinity of the active elements with the oxygen in oxide ceramics[3] or the carbon and nitrogen in carbide[4,5] and nitride ceramics,[6,7] respectively. In general, the active fillers can be divided into three groups, according to their melting points. (1) Low-melting-point active fillers:[8] those with a melting point below 400 8C, a typical example being the addition of titanium to lead- or tin-based solders. (2) Medium-melting-point active fillers:[3] those with a melting point between 700 8C and 1000 8C, a typical T.H. CHUANG, Professor, is with the Institute of Materials Science and Engineering, National Taiwan University, Taipei, 106 Taiwan, Republic of China. M.S. YEH, Associate Professor, is with the Department of Mechanical Engineering, Chung-Hua University, Hsin-Chu, 300 Taiwan, Republic of China. Y.H. CHAI, Design Engineering, is with the Micro Design and Development Division, NEC Electronics, Inc., Santa Clara, CA 950528062. Manuscript submitted November 10, 1998. METALLURGICAL AND MATERIALS TRANSACTIONS A
example being the addition of titanium to silver- or silver-copper–based fillers. (3) High-melting-point active fillers:[9,10] those with a melting point above 1000 8C, a typical example being the addition of titanium to platinum-, palladium-, or goldbased noble-metal fillers. Among them, the most common active filler is the eutectic 72Ag-28Cu with an addition of about 3 wt pct titanium. It has been shown that good joints can be obtained with many oxide and nonoxide ceramics by using these kinds of active fillers.[3–6] However, the interfacial thermal stress generated due to the difference in thermal-expansion coefficients of the ceramic and metal during the cooling process after brazing might deteriorate the joints. To solve this problem, lowmelting-point a
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