Research On Brazing Process And Mechanism Of SiO₂ Ceramic And TC4 Alloy Using Nano Filler Metal

SiO₂ ceramics are widely used in aerospace industry due to its excellent physical and chemical properties.In the aerospace Industry,SiO₂ ceramics could be applied as engine bay of a solid rocket engine,thus the SiO₂ ceramic would be bonded to the TC4 titanium alloy.At present,the ceramic engine bay were bonded to the TC4 titanium alloy mainly by mechanical connection,which produced negative weight to the structure.Vacuum brazing was used to complete the joining of SiO₂ to titanium alloy.In order to optimize the performance of TC4/SiO₂ joint,the nano AgCuNi + Al₂O₃ composite nano filler had been developed.The quality ratio of Ag and Cu was Ag:Cu = 72:28,then the nano AgCuNi + Al₂O₃ composite filler was used for the brazing of SiO₂ to TC4.The impacts of contents of Ni and Al₂O₃ nanoparticles,the brazing temperature and holding time on the microstructure and mechanical properties of the joint were studied,then the optimum contents of Ni and Al₂O₃ nanoparticles were obtained,and it could be found that only when the contents of Ni and Al₂O₃ nanoparticles were at a reasonable range,could the high quality joints be acquired.The evolution of microstructure of the joint was analyzed.The effect of Ni content on the brittle phases in the joints and the effect of nano Al₂O₃ powder particles on eutectic reactions were investigated.The maximum shear strength of the joint was achieved at 950? for 10 min using nano composite filler.And its typical interfacial microstructure was: TC4/?-Ti/?-Ti + Ti₂?Cu,Ni?+ Ti₂?Ni,Cu?hypereutectoid structure/?-Ti + Ti₂?Cu,Ni?+ Ti₂?Ni,Cu?hypereutectic structure/Ti₂?Cu,Ni?+ Ti₂?Ni,Cu?/?-Ti + Ti₂?Cu,Ni?+ Ti₂?Ni,Cu?hypereutectic structure/Ti₄O₇ + TiSi₂/SiO₂ ceramic.With the increasing of the brazing temperature and the extension of the holding time,the amount of ?-Ti + Ti₂?Cu,Ni?+ Ti₂?Ni,Cu?hypereutectic structure in the brazed seam had increased.Comparing interface microstructure and mechanical properties of the joints got by nano filler and micron filler,it could be found that the joint achieved by nano filler was superior to the that by micron filler.Due to low melting point of the nano powder,the nano filler could lower the brazing temperature and reduce the holding time.The diffusion and dissolution behaviors of Ti in the base material had been analyzed.In order to explore the variation of Ti concentration in the filler,a physical model for the dissolution of titanium alloy by liquid filler had been established.At first,the control equation of the dissolved quantity of titanium alloy had been derived.Based on the control equation and the optimum solubility of titanium alloy,formulating reasonable brazing process parameters to prevent corrosion of titanium alloy became possible.According to the theory of brazing and the experimental data,the growth kinetic mathematical model of reaction layer at SiO₂ side was established.Through solving kinetic parameters obtained in the model,the growth kinetic mathematical equation was deduced to reveal the relationship between the reaction layer thickness and the brazing temperature and holding time.