Interfacial Microstructure And Mechanical Properties Of Ti₂AlNb/TC4 Vacuum Brazed Joint

Ti₂AlNb alloy has a broad application prospects in the field of aerospace because of its high specific strength,specific stiffness,fracture toughness and good oxidation resistance.TC4 alloy with?+?dual phase structure has high tensile strength at room and high temperature,good corrosion resistance,good resistance to oxidation and creep resistance at high temperature.The realization of the connection between the two alloys has a great significance in the manufacture and production of parts and components in the aerospace industry.These parts are lightweight and meet the actual requirements.The purpose of this study is to realize the brazing connection between Ti₂AlNb and TC4 alloy.The two kinds of Ti-Zr-Cu-Ni and Ti-Zr-Cu-Ni+Mo filler alloys are used to connect the two alloys.The influence of different process parameters and Mo content on the microstructure and mechanical properties of the joint was studied.The mechanical properties of the joint were improved by controlling the brazing parameters.Ti₂AlNb and TC4 alloys were brazed under different brazing process parameters using 37.5Ti-37.5Zr-15Cu-10Ni?wt.%?.The interface of the joint was characterized by SEM,XRD and EDS.The interface was mainly composed of a diffusion layer near the two base materials and a middle layer of brazing seam.The middle layer was composed of matrix and bulk structure.The typical interface structure from TC4 to Ti₂AlNb side was TC4/?-Ti+??-Ti+?Ti,Zr?₂?Cu,Ni??/?Ti,Zr?₂?Cu,Ni?+?-Ti+?-Ti/Ti-rich/Ti₂AlNb.?Ti,Zr?₂?Cu,Ni?phase was the matrix phase of the brazing intermediate layer,and bulk structure was composed of?Ti,Zr?₂?Cu,Ni?+?-Ti and the residual?-Ti.The hardness of the matrix phase?Ti,Zr?₂?Cu,Ni?was the highest.At980°C/10 min,the brazing joint has the highest shear strength at room temperature of351 MPa.The joint mainly broken along the matrix phase?Ti,Zr?₂?Cu,Ni?,and the fracture pattern belonged to the typical brittle fracture.The average shear strength tested at 500°C and 600°C of the joints under the optimum brazing parameters was307 and 272 MPa,respectively.In order to improve the microstructure and mechanical performance of the joint,Ti₂AlNb and TC4 alloy were joint by Ti-Zr-Cu-Ni+Mo composite filler alloys with different Mo content.The effect of Mo content on the microstructure and mechanical properties was studied.The results showed that,on the one hand,the addition of Mo increased the nucleation rate and the bulk structure in the interface,and the brittle matrix phase?Ti,Zr?₂?Cu,Ni?decreased.On the other hand,the Mo element belongs to?-Ti stabilizing elements,so that the residual?-Ti in the joint increased.When the Mo content was 8 wt.%,the shear strength of the joint was the highest,reaching 437 MPa,which increased by nearly 24%compared with Mo-free joint.The average shear strength of Ti₂AlNb/Ti-Zr-Cu-Ni+8 wt.%Mo/TC4 joints at 500°C and 600°C was395 MPa and 393 MPa,respectively,which reached 90%and 89%of the shear strength at room temperature.