Study On Active Brazing Of Carbon Fiber Reinforced Silicon Carbide Ceramic Matrix Composites

Carbon fiber reinforced silicon carbide ceramic matrix composites(Cf/SiC)are widely used in aerospace and other industrial fields because of their high temperature strength,low density,good corrosion resistance,excellent wear resistance and oxidation resistance.In this paper,the active brazing of Cf/dSiC composites with Ag-Cu-Ti pasty filler metal and Ag-Cu+Ti composite solder with different titanium content was studied.Wettability tests showed that neither Ag-Cu paste filler metal nor Ag-Cu foil could wet Cf/SiC composites.When Ag-Cu-Ti pasty filler metal was used for active brazing,it was found that the wettability of Ag-Cu-Ti paste filler metal decreased with the increase of Ti content.When Ag-Cu+Ti composite solder was used for brazing,it is found that the wettability of Cf/SiC composites increased with the increase of titanium content.When the content of titanium powder exceeds 5%,the composite solder showed complete wettability to Cf/SiC composites.Through metallographic observation and energy spectrum analysis,when Ag-Cu-Ti pasty brazing filler metal containing 2%titanium was used,the Ti-rich reaction layer was found at the interface between Cf/SiC composite and brazing metal.With the increase of titanium content,titanium reacts with copper rapidly in the welding process and quickly fixes in the brittle and hard Ti-Cu rich phase,the Ti-Cu rich phase increases and the interfacial reactants decrease.The results showed that when the titanium content in the composite solder does not exceed 10%,as the titanium content increases,the interfacial reactants on the interface between the Cf/SiC composite and the brazing metal interface generated,from random to continuous.When welding with Ag-Cu + Ti alloy containing 2.5%titanium,it was found that a small amount of titanium element entered the brazing metal and had a strong refinement effect on the copper-rich solid solution phase inside the brazing joint.When the titanium content continues to increase,the Ti-Cu rich phase in the brazing metal gradually increases.Mechanical properties experiments showed that all the shear specimens were fractured in the Cf/SiC composites or in the Cf/SiC composites and in the holes in the brazing seam.Studied have shown that titanium is a key element in achieving active brazing.Titanium can react with Cf/SiC composites to improve the wettability of solder and form a firm interface.When the interface is carbon fiber,the interface reactant is mainly TiC.When the interface is silicon carbide,the Ti-rich layer is mainly Ti-Si-C compound.Titanium mainly reacts with copper in the brazing seam metal,compared the brazing seam metals of Ag-Cu-Ti paste filler metal and Ag-Cu+Ti composite solder,it was found that the brazing seam obtained by the latter was more uniform in structure and element distribution,and had better comprehensive performance.