Research On Mechanism Of Brzaing TC4 And C/C Composite With Carbon Fiber Reinforced Composite Filler

C/C composite is an excellent engineering material,but the brittleness makes its application fields restricted.TC4 alloy is often required to join with C/C composite,which is helpful to expand the advantages of the two kinds of materials.However,due to the great difference in physical properties between the two materials,it is easy to generate large residual stress at the brazed joints,which will deteriorate the joints.Therefore,the reinforcement phase with low coefficient of thermal expansion is often added to filler to form stress transition to reduce the peak stress.With good physical and mechanical properties,carbon fiber has been widely used as reinforcing phase in the process of manufacturing composite materials.Therefore,based on the idea of improving the brazed joints,carbon fiber reinforced AgCuTi filler was used to braze C/C composite and TC4alloy and the optimum process was explored.Before brazing,it is necessary to study the effect of carbon fiber on the characteristics of filler,which is helpful to understand the reinforcement mechanism of carbon fiber during brazing.Therefore,a single filler system was designed to study the effect of carbon fiber on the reaction path,the binary system of the composite filler and C/C composite was used to study the influence of carbon fiber on the spread of filler,the ternary system of composite filler,C/C composite and TC4 alloy was adopted to explain the reinforcing mechanism of carbon fiber.The interface behavior of carbon fiber was analyzed step by step.Finally,the process of joint formation was analyzed and the role of carbon fiber in each stage of joint formation was revealed.The results show that metallurgical reaction did not occurred in the preparation process of filler.Carbon fiber was evenly distributed in the AgCuTi filler and did not change the melting temperature of the filler(780?).The reaction path of AgCuTi filler was analyzed in the present work.The Ti₃Cu₄,not TiCu,was formed during the process of isothermal precipitation.The growth of Ti₂Cu₃ was very slow during the transformation of Ti-Cu compounds,which was the transition phase in the reaction process.The distribution of elements was changed by carbon fiber in AgCuTi filler.The addition of carbon fiber could change the reaction path of AgCuTi filler,and turned the Ti-Cu compounds to TiC+Cu(s,s).Carbon fiber had significant influence in the spreading process of AgCuTi filler on the surface of C/C composite.With the increase of carbon fiber content,the spread area of filler increased first and then decreased,while the contact angle remained unchanged.The results showed that the AgCuTi filler was separated into two kind of liquid phases after melting.Due to the difference of density,the liquid phase L₁ spread to both sides,while the liquid phase L₂ stayed in the middle region of filler.A small amount of carbon fiber could promote the outflow of L₁,reduce the spreading resistance of liquid phase and increase the spreading area.However,excessive carbon fiber could inhibit the outflow of L₁,increase the spreading resistance of liquid phase and reduce the spreading area.The formation mechanism of C/C-TC4 joints with AgCuTi filler were analyzed.The TiCu layer was precipitated firstly on the side of TC4 alloy,which is linked to the adsorption of Ti dissolved on the TC4 side to Cu.The excessive formation of Ti-Cu compounds in the central area of brazing seam and reaction layer was related to the increased Ti activity.With the addition of carbon fiber in AgCuTi filler,the Ti activity in the non carbon fiber area was regulated,and the joint strength was improved.The maximum strength of 28.5MPa was obtained when the carbon fiber mass fraction was0.3%.The optimum parameter of C/C/AgCuTi+0.3%C_f/TC4 joints was explored,which was 900?/10min.The activity of Ti increased with the increase of brazing temperature and time.The formation process of C/C/AgCuTi+C_f/TC4 joints could be divided into four stages:melting of filler,dissolving of TC4 alloy;element enrichment,the formation of reaction layer;isothermal precipitation,the movement of liquid phase;joint formation.Carbon fiber played an important role in the formation of the joint,which regulated the microstructure and residual stress of the brazed joint and improved the mechanical property of brazed joint.