Microstructural evolution at the bonding interface during the early-stage infrared active brazing of alumina
- PDF / 1,078,431 Bytes
- 10 Pages / 612 x 792 pts (letter) Page_size
- 3 Downloads / 199 Views
I. INTRODUCTION
WITH the rapid development of ceramics, superalloys, and composite materials, traditional ways of brazing are insufficient to meet the requirement of joining these materials. Traditional brazes cannot make a good joint between ceramic materials due to the difficulty of wetting, even when their surfaces are clean.[1–4] Most structural ceramics, e.g., alumina, silicon carbide, and zirconia, are chemically more stable than metals, and they will not be wetted by traditional brazes unless the braze contains an active element. Active brazing is a process using a braze filler alloy containing an active element such as Ti, Zr, V, and Cr.[2,4,5–10] For example, titanium is one of the most frequently used elements as an active constituent of silver-base active braze alloys.[6,7,9,10] Moreover, the active element in the braze can only be effective if sufficiently high temperatures are used for the joining operation so that the active ingredient is able to react with the ceramics.[2,11] Therefore, the active ingredient plays an important role in active brazing. The activity of the active element in braze is very important, since it dominates the mechanism of reactive wetting during active brazing. For example, the active element cannot strongly react with other element(s) in the braze alloy, or the activity of the active element may be greatly decreased by formation of intermetallic compounds. Much research has demonstrated that Ti is an active element in copper and silver-base braze alloys.[7,10,11] The addition of Ti to silver/copper alloys improves the wettability of many ceramics.[12–16] There are many commercially available active braze alloys in use.[4,17] Ag-Cu eutectic with 4.5 wt pct Ti is one of the most popular active silver-base braze alloys used in metal-ceramic joining.[18,19,20] R.K. SHIUE, Assistant Professor, is with the Institute of Materials Science and Engineering, National Dong Hwa University, Hualien 974, Taiwan, Republic of China. S.K. WU, Professor, and J.M. O, former Graduate Student, are with the Institute of Materials Science and Engineering, National Taiwan University, Taipei 106, Taiwan, Republic of China. J.Y. WANG, Deputy Section Head, is with the Materials R&D Center, Chung-Shan Institute of Science and Technology, Lung-Tan 325, Taiwan, Republic of China. Manuscript submitted November 29, 1999. METALLURGICAL AND MATERIALS TRANSACTIONS A
Much research has focused on the interfacial reaction kinetics between active filler alloy and ceramics.[21–25] Most of these studies are performed by traditional electric resistance heating. However, it is difficult to study the interfacial reaction kinetics in the early stage of active brazing if the heating rate of furnace is not fast enough. For instance, the melting point of Ag-Cu eutectic alloy is 780 8C. Titanium will be dissolved into Ag-Cu eutectic melt for temperatures above 780 8C. The brazing temperature of Ag-Cu eutectic with 4.5 wt pct Ti alloy is 900 8C. The heating rate of the electric resistance heating furnace is 10 8C/min, and
Data Loading...
