Study On Processing And Mechanical Properties Of Diffusion Bonded Joints Of Ti₂AlNb Alloy

Ti₂AlNb based alloys were widely applied in the aerospace field due to attractive properties such as high strength-to-density,excellent room temperature ductility,fracture toughness,creep resistance,good oxidation resistance and nonmagnetic property.In many aerospace applications,it is necessary to join individual components into large and complex assemblies.Therefore,the development of joining techniques to fabricate high-quality joined components is indispensable for engineering applications.In this study,TLP bonding and solid diffusion bonding was applied to join Ti₂AlNb alloy.The effects of bonding temperature and time on the microstructure and mechanical properties of the joints were studied.In addition,Different interlayer was used to control interfacial microstructure and improve mechanical properties.Ti₂AlNb alloy was successfully joined by TLP bonding technique using Ti/Ni interlayer.The interface microstructure was characterized by SEM?EDS?TEM and XRD.The reaction phases formed in the bonded joint were Nb₃Al,B2,?₃ and Ti₂Ni.The maximum RT shear strength reached 428MPa when the joint was bonded at1180°C for 20min.In addition,the shear strength of the joints tested at 500°C,650°C and 800°C was 423MPa,407MPa and 338MPa,respectively.The formation of?₃phase with the highest E and H was detrimental to the bonding properties,especially a continuous?₃ compound layer formed in the center of the joint.Solid diffusion bonding was applied to joint Ti₂AlNb alloy.The microstructure and mechanical properties of the joints were investigated.The maximum shear strength achieved was 538 MPa when the joint was bonded at 950°C for 60min.Fracture of the joints was primarily propagated in the bonded interface,and partially traversed Ti₂AlNb alloy.Ti foil was used to join Ti₂AlNb alloy in order to decrease bonding temperature.The interface microstructure and mechanical properties was markedly affected by bonding temperature and time.The maximum RT shear strength reached 664MPa when the joint was bonded at 960°C for 60min.The failures of the joints occurred in zone II.Fracture morphology of the bonded joint was dimple pattern with features of ductile fracture.