Study On Contact-reactive Brazing Process Of Ti₃SiC₂ Ceramic And TC4 Alloy

Ti₃SiC₂ ceramic combines excellent characteristics of metals and ceramics,such as easy machinability,good thermal and electrical conductivity,high melting point and excellent corrosion resistance,which has been considered as promising materials in the fields of nuclear energy,corrosion resistant electrode,aeronautics and astronautics.TC4 alloy is widely applied in the fields of oceaneering,biomedical science,aeronautics and astronautics because of its high specific strength,low modulus of elasticity and excellent corrosion resistance.Well-bonded Ti₃SiC₂ ceramic and TC4alloy joint can widen the application of the two materials as it possesses the characteristics of Ti₃SiC₂ ceramic and TC4 alloy.Ti₃SiC₂ ceramic and TC4 alloy were contact-reactive brazed using a Ni interlayer or/and a Cu interlayer,well-bonded joints were obtained,and the brazing process and mechanism of the joints were investigated.With the increase of bonding temperature micro-voids appeared nearby the TC4alloy side in the brazed joints using a Ni interlayer;prolonging the holding time,the amount of dissolved parent materials and the width of reaction layer increased;with the increased thickness of Ni interlayer,the size of the brazing fillets increased and micro-cracks appeared nearby the brazing fillet.The shear strength first increased then decreased with the increase of bonding temperature,holding time and the thickness of Ni interlayer.The maximum shear strength,126MPa,obtained by the joints brazed at 1000°C for 10min using a 30-?m Ni interlayer,the fracture occurred in the reaction layer and the Ti₃SiC₂ ceramic.Less parent material dissolved in the contact-reactive brazed joints using a Cu interlayer.Moreover,the width of the brazing seam and bonding temperature decreased,and the coarsening grains of TC4 alloy were depressed.The joints were composed of diffusion layer,athermal solidified zone and Ti-Si reaction layer.With the increase of bonding temperature,the reaction of diffusion atoms became more active and the fluidity of liquid phase in the joints improved.Thus,the width of the diffusion layer and the Ti-Si reaction layer increased,and the athermal solidified zone decreased.The maximum shear strength,132MPa,obtained by the joints brazed at920°C for 10min using a 50-?m Cu interlayer.According to the analysis of fracture surface and micro-hardness of the joint,the continuous Ti-Si reaction layer was the weakest positon of the joints.Plated Ni layer Ti₃SiC₂ ceramic was brazed to TC4 alloy using a Cu interlayer,the continuous Ti-Si reaction layer disappeared and the maximum shear strength of the joint was improved to 142MPa,and the fracture mainly occurred in the Ti₃SiC₂ ceramic.