Wettability and bonding of graphite by Sn0.3Ag0.7Cu-Ti alloys

The wettability of graphite by SnAgCu-Ti alloys was investigated by sessile drop method in vacuum. Bonding of graphite to itself using SnAgCu-Ti alloys was carried out and the joint strength was evaluated by shear test. Active element Ti began to react with graphite at 600 °C and TiC interfacial reaction layer was formed, which resulted in the decrease of contact angle. It had a continuous decrease as temperature elevated. In isothermal process, a lower contact angle was obtained at a higher isothermal temperature resulting from the decrease of the stoichiometry of TiCx. The spreading activation energy of SAC-Ti on graphite surface was 182.66 kJ/mol. Desirable graphite/graphite joint was obtained by direct brazing using SnAgCu-Ti in vacuum. The typical microstructure of brazed joint was graphite/TiC/β-Sn containing Ti6Sn5/TiC/graphite. The shear strength of direct brazed joints varied from 17.6 to 20.6 MPa. Reliable joint was bonded without any filler metal in atmosphere at 250 °C after graphite metallized by SnAgCu-Ti. A favourable shear strength of 20 MPa was achieved. Pre-metallized graphite by SnAgCu-Ti decreased the bonding temperature and guaranteed the bonding strength.

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