Wetting and Brazing of Alumina by Sn0.3Ag0.7Cu-Ti Alloy
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ALUMINA ceramics are used widely in electronics for their low thermal expansion and good thermal conductivity.[1,2] Recently, active brazing methods have emerged as a new and convenient way to join alumina ceramics to themselves or to metals. In this approach, a small amount of active elements (Ti, Cr, Zr etc.) are alloyed into brazing metal.[3–7] These active elements could significantly enhance wettability on ceramic by interfacial reactions.[8,9] Voytovych et al.[10] found that contact angles reached as low as 10 deg in CuAg-3Ti (wt pct)/alumina system and they attributed this to the formation of metal-like Ti3Cu3O and Ti4Cu2O on the interface. Meanwhile, in reactive brazing, interfacial reactions were also found to facilitate bonding.[11,12] Ali et al.[13] obtained reliable joints of alumina/alumina using Ag-35.3Cu-1.8Ti at 1088 K and 1148 K (815 °C
J.R. KANG, S.P. HU, and W.J. GUO are with the School of Materials Science and Engineering, Harbin Institute of Technology at Weihai, Weihai 264209, China. X.G. SONG, D. LIU, W. FU, and J. CAO are with the State Key Laboratory of Advanced Welding and Joining, Harbin Institute of Technology, Harbin 150001, China and also with the School of Materials Science and Engineering, Harbin Institute of Technology at Weihai. Contact e-mail: [email protected] Manuscript submitted June 1, 2017.
METALLURGICAL AND MATERIALS TRANSACTIONS A
and 875 °C). Ti3Cu3O and c-TiO were observed on solder/alumina interface. Among various kinds of active brazing alloys, Sn based brazing metals have received focused attention for their low cost and promising alternative as lead-free solders.[14] Gremillard[15] and Saiz[16] studied the wettability of molten Sn3Ag1Ti on alumina at 837 K to 1273 K (564 °C to 1000 °C) and found that an addition of 1 wt pct Ti added into Sn3Ag brought the equilibrium contact angle down to 23 deg with titanium oxide observed on Sn/sapphire interface. However, in active brazing, intermetallic compounds (IMCs), such as Ti6Sn5, and Ti5Sn3, were often observed in the brazing seam due to high reactivity of active elements.[6] Apart from deteriorating joint mechanical properties,[17] IMCs were also reported to exert adverse impacts on wettability. Fu et al.[18] studied the wettability of SnAgCu-xTi (x = 2, 4, 6, 8, 10, wt pct) on AlN and found that wetting and spreading of high Ti containing droplets were inhibited owing to the intense formation of Ti-Sn IMCs. Generally, the formation of these IMCs is inevitable. Therefore, it is of crucial importance in active brazing to alloy moderate amounts of active elements to ensure wettability and interfacial bonding while limited IMCs form in the brazing seam. Further investigations are needed to demonstrate the adverse impact of IMCs on wetting quantitatively. This could provide theoretical support to the design of active brazing alloys.
In the present work, wetting experiments of Sn0.3Ag0.7Cu (SAC)-Ti alloy on alumina were conducted by the sessile drop method at 1223 K, 1273 K, and 1323 K (950 °C, 1000 °C, and 1050 °C
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