Surface modification on wetting and vacuum brazing behavior of graphite using AgCu filler metal

Joining of graphite materials is problematic primarily due to the poor wettability of non-active filler metal on these materials. In an attempt to overcome this problem, magnetron sputtering deposition of Cr film on graphite was performed to modify the surface of the graphite. The wetting and brazing of graphite are carried out using non-active AgCu eutectic filler metals after deposition. The results indicated that surface modification enables wetting and joining of graphite with non-active filler. Cr film reacted with graphite forming Cr-C interfacial reaction layer, which resulted in the decrease of contact angle. Reliable graphite/graphite joints were obtained at temperature from 1113 K to 1233 K for 10 min. The typical interfacial microstructure of the brazed joint is graphite/Cr-C layer/Ag(s,s) + Cu(s,s) eutectic phase/Cr-C layer/graphite. The optimal shear strength of the joint was 13.6 MPa when the brazing parameters were 1173 K for 10 min.