Brazing Of Ceramic By Self-oxide Film Removing Al Foil Filler

The special performance advantage of ceramic materials has been applied more and more attention in modern industry.Brazing is the one of the most important and indispensable ways of ceramic bonding.Since most ceramics cannot be directly wet by metals and do not react with them,it is inevitable that a reactive transition layer exists in the joints to improve the wettability of metals on ceramics with the brazing filler based on Cu,Ag and Ni.However,the performance of joints is reduced.Al not only have the structure and properties same with Cu,Ag,Ni base of brazing filler,but also can be more able to wet Al₂O₃ and Al N important engineering ceramics without reaction transition layer and without any chemical reaction.But Al gets an oxide layer and is extremely difficult been removed,Al and its alloys have not become the brazing filler for ceramics.Based on the studies of our team about brazing ceramics with Al film filler,this paper proposed a kind of coated Al foil filler and studied the mechanism of this filler removing the surface oxide film.Two kinds of brazing method to improve the joint strength through hot wetting and"sputtering wetting".The main conclusions are as followed:1.Using sputtering technology to depose Ni/Al and Si/Al double film on Al foil filler which can bury the oxide film on Al foil filler.The oxide film will be broken in the process of brazing and be involved in liquid Al.The Ni and Si double film can be redacted by Al liquid,the brazing filler can remove the oxide layer by itself in the physical way.This characteristics and advantages can realize the direct brazing of Al₂O₃and Al N ceramics without any transition layer.2.The improvement of wettability and interfacial strength can significantly improve the strength of the Al-ceramic brazing joint by improve the brazing temperature,and the shear fracture of the joint can be gradually transferred from the interface to the metal of the joint.In Al-1at.%Ni alloy brazing joint of Al N,at 680°C,the shear strength of joints is 79 MPa,the fracture occurred in the brazing seam metal and Al N interface,with the improvement of brazing temperature and wettability improvement,joint fracture gradually transferred to the brazing seam metal,strength also gradually increase to 146 MPa at 840°C or more than.In Al-1at.%Si alloy brazing joint of Al₂O₃,at 680°C,the shear strength49 MPa of the joints,fracture occurred in the brazing seam metal and Al₂O₃interface,with the improvement of brazing temperature and wettability improvement,joint fracture gradually transferred to the brazing seam metal,strength also gradually increase to 158 mpa at 840°C or more than.3.The results of precoated Al film on surface of Al₂O₃ ceramics hows that hi sputtering Al directly on the surface of ceramic particles can produce a kind of"sputtering wetting’effect with high energy,this effect can make Al after the melting of the 680°C can realize the wetting of l₂O₃,under this temperature brazing joints can get 160 MPa of shear strength and the fracture occurred in the brazing seam metal which is the same as the ceramic without coating Al film at 840°C,and the fracture is in a similar way.