Research On Process And Mechanism Of Reaction Brazing Of C/SIC And C/C Composite To Nb

C/SiC and C/C composites prossess superior properties such as:low density,high specific strength,high temperature fracture toughness,good temperature resistance,ablation resistance,oxidation resistance,abrasion resistance and corrosion resistance.As a result,they have been extensively used in fields of aeronautics,astronautics and nuclear industries.Specificlly,at present,C/SiC and C/C are applied in fabricating the thrust chamber nozzle of the aircraft engine.And Nb is used to fabricate the metal transit ring.To realize the sound brazing of C/SiC and C/C to Nb,can breakthrough the technology of novel aerospace engine thrust chamber manufacturing.In this study,TiNi composite foils filler with equal atomic ratio were used to braze C/SiC and C/C composite to Nb.The interfacial microstructure and mechanical properties of the joints were investigated.And composites processing technology of laser-drilling was utilized to enhanced the brazed joints.The development of thrust chamber brazing joints were achieved.In order to analyze the interactions of the filler alloy and substrates,the contact reaction between TiNi composite foils filler and Nb substrate were studied,and the formation mechanism of TiNiNb liquid was obtained.Base on the analysis of the Nb dissolution in TiNiNb liquid,the theoretical equation for calculating the amount of Nb dissolving was established.According to the measuring results of Nb dissolving width under different holding time,the expression of the Nb dissolving width on holding time was determined.Aiming to realize the joining of C/SiC composite and Nb,TiNi composites foil were used to directly braze C/SiC and Nb,the interfacial reaction products are:C/SiC side reaction layer?Ti,Nb?C,?Ti,Nb?₂Ni compounds,Ti-Ni-Nb-Si compounds and TiNi-Nb?s,s?eutectic.When the brazing temperature is 1180?and the holding time is 20min,the room temperature?20??and 600?,800?,1000?high temperature shear strengths are 192MPa,155MPa,115MPa and 82MPa,respectively.During the shear fracture occurs,cracks initiated from the fillet on the C/SiC surface,and propagated near the interface of C/SiC and brazing seam.Meanwhile,The direct brazing of C/C composite and Nb were also carried out with TiNi composite foils,the interfacial reaction products are:C/C side reaction layer?Ti,Nb?C,?Ti,Nb?₂Ni compounds and TiNi-Nb?s,s?eutectic.When the brazing temperature is 1200?and the holding time is 20min,the room temperature?20??and 600?,800?,1000?high temperature shear strengthes are 42MPa,34MPa,25MPa and 18MPa,respectively.The shear fracture of the joint occur red inside the C/C and near the interface of C/C and brazing seam.It is significant to enhance the joining properties and improve the application reliability of.Therefore,laser-drilling technology to process the surfaces of composites was proposed based on the direct brazing.The interface of laser-drilling brazed joint of C/SiC composite and Nb can be divided into the non-drilling zone and drilling zone.The reaction products in both zones are:C/SiC side reacti on layer?Ti,Nb?C,?Ti,Nb?₂Ni compounds,Ti-Ni-Nb-Si compounds and TiNi-Nb?s,s?eutectic.The optimized processing parameters of laser drilling are drilling diameter?1mm,drilling depth 1.5mm.And the room temperature?20??and 600?,800?,1000?high temperature shear strengths reached 259MPa,186MPa,161MPa and122MPa,respectively.Which are higher than those of direct brazing joints.The fracture of the brazed joints occurred inside the C/SiC and near the interface of C/SiC and brazing seam.The enhancement mechanism of laser drilling on C/SiC and Nb brazed joints was studied by theoretical calculation and finite element modeling analysis,respectively.The calculated results show that the contribution of infiltrated filler to the shear strength of joints is about 50-67MPa.The results of finite element simulation show that the residual stress concentrated position migrated from the fillet to the inside of C/SiC composite in the laser drilling joint,thus the bearing capacity at the fillet can be improved.Meanwhile,the residual stress peak of the joint migrated to the bottom of the laser-drilling hole,and the residual stress of the joint reduced from 440MPa to 338MPa,the reduction is up to23%.The laser-drilling processed C/C composites were brazed to Nb,the reaction products in the laser-drilling hole are:C/C side interface reaction products?Ti,Nb?C,?Ti,Nb?₂Ni compound and TiNi-Nb?s,s?eutectic.It worth noting that the C/C composite at the hole walls fragmented.Due to the relatively poor strength of C/C composite,laser drilling could deteriorate the C/C properties.The strengthening of the brazed joints can not be achieved consequently.Therefore,Nb mesh interlayer was designed.Nb has good ductility,moreover,Nb mesh can provide the elements diffusion channel and inhibit the formation of the compounds in braze seam.As a result,the shear strengths of C/C composite and Nb brazed joints at room temperature?20??,600,800 and 1000?can be improved to 60MPa,51MPa,45MPa and 38MPa respectively.The processing parameters of brazing and laser-drilling were optimized,and the corrosion defect of Nb transit ring was controlled.The development of C/SiC composite thrust chamber brazing joint components was carried out.The brazed joints passed the ground and high altitude heat tests and meet the quality requirements.