Study On Technology And Mechanism Of Self-propagating Reaction Assisted Brazing Between Gr/2024Al Composite And TC4Alloy

In order to meet the demand of the joining of advanced high temperature materialsin aerospace fields, and to maintain the superior property of Gr/2024Al composite,self-propagating high-temperature synthesis (SHS) assisted brazing of Gr/2024Alcomposite and TC4alloy was performed. Combining the theoretical analysis andexperimental investigation, the composition of SHS interlayer was optimized. Themicrostructures as well as mechanical properties of the joints were investigated. TheSHS reaction mechanisms of the interlayers were analyzed. The effects of filler alloyunder high cooling rate were studied. And the characterized microstructure evolutionwas investigated.The TiAlCCu interlayer was utilized to conduct the SHS assisted brazing ofGr/2024Al and TC4with AgCuTi filler alloy. The typical interfacial microstructure ofthe joint is: Gr/2024Al composite/Ti3AlC2/Ag(s.s)+Al4Cu9+Al5CuTi2/Ti+TiAl3+Al5CuTi2+Ag-Al+C/TiAl3/TC4. When preheating temperature is650℃,holding time is15min, the maximum shear strength at room temperature can beobtained, which is11MPa; the shear strength at300℃is8MPa. The fracture initiatesfrom the composite/braze seam interface and propagates into the composite. The joiningmechanism was studied and the effects of C powder agglomeration on joining propertieswere investigated.To avoid the agglomeration of C powder and improve the joining properties, NiAlinterlayer was proposed to perform the SHS assisted brazing of Gr/2024Al and TC4with AgCuTi filler alloy. The typical microstructure of the joint is Gr/2024Alcomposite/Ti3AlC2/Ag(s.s)+Al4Cu9+Al5CuTi2/Al(Cu,Ni)/Ni+Ag(s.s)+NiAl+Ni3Al+Ni2Al3/Al(Cu,Ni)/Al(Cu,Ni)+CuNi+Ti(Cu,Ni)/TiCu/TC4. The optimum compositionof the interlayer is50%Ni50%Al, and the particle sizes of Ni and Al are10m and7m,respectively. When the preheating temperature is670℃, holding time is15min, themaximum shear strength at room temperature can be obtained, which is13MPa; theshear strength at300℃is9MPa. The fracture occurred inside the Gr/2024Alcomposite.Using combustion front quenching method and characteristic temperature method,the mechanism of the SHS of NiAl was analysed. In preheating stage, the solid statediffusing of Ni and Al conducted. When liquid formed, Ni began to dissolve into theliquid. With the precipitating of NiAl compound, uniform NiAl structure formed in theinterlayer. The characterized morphology of filler alloy after joining was investigated,and the results show that, due to the SHS reaction, the braze seam cooled rapidly, leading to the nonequilibrium solidification of the filler alloy, the braze are mainlycomposed of supersaturated Ag-base solid solution, no segregation of Al and Cu can bedetected. As a result, the characterized morphology different from conventional AgCueutectic structure can be produced.