Research On Processing And Mechanism Of Brazing C/C Composite And TC4 Titanium Alloy

C/C composite has good mechanical properties and can resistant to high temperature.Also,C/C composite has characteristic of low density,high thermal conductivity and low thermal expansion coefficient.Now it’s widely used in the field of aerospace technology.C/C composite is always used to join with TC4 alloy.One of main problems in the process of joining this two matertials is that the difference of linear expansion coefficient between the two matertials is too large,which lead to the high residual stress in the brazed joint.In order to reduce the residual stress,in this paper,we use laser cladding to clad layer of WC particles layer and Cu-Ni-WC composite solder layer to achieve joint with high quality between TC4 and C/C composite.By method of laser cladding,At first we prepared thr WC particle layer,and then we preparated the Cu-Ni-WC composite solder layer.By adjusting the laser power,powder feeding rate and scanning speed of laser,we obtain the optimum preparation of the two cladding layers.The optimum preparation of WC particles layer is: P=1900W,VP=5g/min,VS=4mm/s;The optimum preparation of Cu-Ni-WC composite solder layer is: P=1000W,VP=3g/min,VS=4mm/s.The layers prepared by the optimum preparation have good and smooth forming.After that,the paper studied the microstructure and mechanical properties of cladding layer.The WC particles layer has high hardness.W2 C and TiC compound generate in the WC particles layer.The Cu-Ni-WC composite solder layer has low hardness,which is mainly contains CuNi solid solution.After we find the optimum preparation of the two layers,the paper uses the Ti foil to braze TC4 and C/C composite.After the brazing,the typical interface of the joint is analyzed.The typical interface is as follows: C/C composite/TiC/Ti(Cu,Ni)+Ti2(Cu,Ni)+WC+W2C/TiCu2+TiNi3/CuNi solid solution+WC+W2C/Ti(Cu,Ni)/WC+W2C+TiC/ TC4.Then we change the brazing parameters.The microstructure and mechanical properties of the joint in different brazing temperature and holding time is researched.The reserch finds the optimum preparation of joint is: 950℃,15 min.Based on the analysis of mechanical properties on typical objects in the joint.We know that under this parameter the brazing temperature is low.There are many Ti(Cu,Ni)compounds with fine plasticity distribute in the brazing joint and The Ti2(Cu,Ni)compounds distribute discretely in the brazing joint.The thickness of TiC layer is appropriate.At this brazing parameter,the shear strength of brazed joint reachs 34 MPa.Then the paper proceeds the thermodynamic analysis on the reactions in of brazed joints.The results show that each reaction can occur spontaneously in the brazing temperature.The research discussed the evoluting mechanism of interface by the Microstructure analysis and thermodynamic analysis.The evolution process consists of four parts,namely the mutual diffusing of brazing material,the formation of filler in liquid phase,the formation of microstructure,the stage of stabilization and cooling.Then the research analysis the mechanism of the laser cladding layers reducing the residual stress by mechanical model.After measuring and calculating the Physical parameter of the materials,the approximate calculation results show that the laser cladding layer makes the residual stress on the C/C composite side decreased significantly.That phenomenon indicates that the laser cladding can make the transition of linear expansion coefficient smooth,which can reduce the residual stress in the brazed joint and make the mechanical properties of the joints improve.The research also interpretated the mechanism of the reliefing in residual stress by Cu-Ni-WC composite solder layer.The CuNi solid solution can relieve residual stress of the joint by plastic deformating.WC granule can reduce the thermal expansion coefficient to relieve residual stress.