Research On The Process And Mechanism Of C/SiC And Nb Brazing

C/SiC composite materials change the brittleness and poor toughness of ceramics through the toughening effect of carbon fiber.It not only has the properties of silicon carbide matrix such as high temperature resistance,corrosion resistance,abrasion resistance,high strength,thermal shock resistance,etc.,at the same time,due to the toughening effect of carbon fiber,it effectively alleviates the shortcomings of the brittleness of the ceramic itself.It can be at 1650?Long-term stable work,short-term use at 2000?,and instantaneous work at 2800?.It is an important member of the new generation of aerospace materials.However,due to its poor machining performance,it is difficult to manufacture structural parts with complex structures or large sizes.It happens that metal Nb and its alloys have good high-temperature properties,have the smallest density among all refractory metals,and can serve steadily at 1100? to1650?.They have excellent welding performance and are a preferred structural material in the aerospace field.We connect the two to realize the application of this joint structure in the aerospace field.When studying the brazing connection of C/SiC composite material and metal Nb,this paper starts from two aspects of residual stress relief that restricts the strength of the joint and its high-temperature performance.First,we design the structure of the ceramic surface through electrochemical corrosion,which is effective Relieve the residual stress of the joint.Secondly,the joints are connected by a new type of high-temperature brazing material Ti-Co,the influence of welding process parameters on the interface structure and mechanical properties of the joints is studied,and the use of Ti foil as an intermediate layer is proposed to optimize the weld structure.Finally,TiC particles are added to the solder to enhance the welded joint.In order to increase the addition of the reinforcing phase,a carbon cloth is used as an intermediate layer to achieve a good connection between the two.The surface structure of C/SiC composite material is controlled by electrochemical corrosion.When the appropriate corrosion process parameters are selected,a certain depth of corrosion structure will be produced on the surface.In this study,when the corrosion depth is 106?m,the joint achieves the maximum shear strength.At this time,the corrosion process parameters are:the corrosion voltage is 1.2V,and the corrosion time is 2h.The interface structure of the joint formed when Ti-Co solder brazing C/SiC composite material and metal Nb is:C/SiC composite material/TiC+Ti₅Si₃ reaction layer/Ti₂Co+(Ti,Nb)solid solution/(Ti,Nb)solid solution/metal Nb.When the brazing temperature is 1130?,the holding time is 20min,and the thickness of the intermediate layer is 200?m,the joint achieves the maximum shear strength.The strength at room temperature is 131.4MPa and the strength at 800?is 81.7MPa.When the intermediate layer is not added,the weld is mainly composed of brittle Ti₂Co.Due to the addition of the intermediate layer,it not only effectively prevents the diffusion of Nb in the base material into the weld,but also reduces the proportion of Ti₂Co in the weld.It is Ti(s,s)solid solution.When the reinforcement particles TiC are added to the Ti-Co solder,the interface structure and mechanical properties of the welded joint are changed.In the welding seam of composite brazing joints,TiC particles are evenly distributed in the welding seam,but when the amount of addition increases,these particles will aggregate,causing defects such as holes in the brazing joint.For this reason,we increased the amount of TiC particles added by designing a carbon cloth intermediate layer.From the final mechanical performance test of the joint,we found that the strength of the joint has been greatly improved.The maximum shear strength is 144.4MPa,which is 47.3%higher than the brazed joint strength of pure Ti-Co solder.