Study On The Diffusion Welding And Properties Of TA2 And TU2

The welding between copper alloys and titanium alloys plays an important role in the development of the industry..For example,in the development of the aerospace industry,it is urgent to replace the current bulky steel cylinder with a titanium alloy cylinder-copper alloy cylinder liner plunger rotor for the combined cylindrical components of the multi-precision friction pair in the aircraft engine constant speed device.a titanium alloy cylinder-copper alloy cylinder liner plunger rotor to reduce aircraft weight and increase specific strength.In this context,the effective connection between titanium alloy and copper alloy will have very important research significance.However,the diffusion bonding strength between titanium and copper is affected by the brittle intermetallic compound formed by the diffusion of Ti and Cu.The formation of intermetallic compounds can be effectively avoided or reduced by using an effective intermediate layer,which is very advantageous for the improvement of joint properties.In this paper,industrial pure titanium TA2 and copper TU2 are selected as the research base materials,and the diffusion bonding of TA2 and TU2 directly and adding Ni,Nb and Ni/Nb as the intermediate layer was realized by vacuum diffusion bonding method.The microstructure and diffusion products of the joint interface were characterized by SEM,XRD,EDS and microhardness tester.The influence of microstructures of welded joints on macro-mechanical properties with different process parameter and intermediate layer were studied.The strength of TU2/TA2 direct diffusion welded joints is lower because brittle intermetallic compounds are formed at the interface.The maximum value was reached at the welding temperature of 800?and the holding time of 30min,which was 67.2MPa.The fracture mainly occurs in the Ti-Cu brittle intermetallic compound layer at the welding interface.The fracture surface is smooth without obvious deformation characteristics.The fracture is mainly carried out in a brittle cleavage manner.The fracture location is in the Cu₄Ti₃ diffusion intermetallic compound layer.Due to the low strength of the direct diffusion joint,the addition of Ni,Nb and Ni/Nb improves the joint performance,and the effect of different intermediate layers on the joint performance is not the same.The increase of the strength of the TA2/Ni/TU2 joint with the addition of the Ni intermediate layer was not significant.At the welding temperature of820?,the maximum value of the joint strength was only 75.6MPa.Mainly formed a new Ni-Ti brittle intermetallic compound at the TA2/Ni interface,which seriously reduces the bonding strength of the joint.The addition of the Nb intermediate layer can obtain a welded joint having a higher tensile strength,and the Ti-Nb solid solution formed at the interface is more advantageous for the joint strength than the brittle intermetallic compound,which improves the joint strength of the joint.When the welding temperature is 860°C and the holding time is 75 min,the tensile strength of the TU2/Nb/TA2 welded joint reaches the value of 129.3 MPa.It is about twice as much as maximum tensile strength of TU2/TA2direct diffusion,The tensile strength of this joint is significantly higher than that of TU2/TA2 welded joint with Ni interlayer.The addition of the Nb/Ni composite interlayer improves the tensile strength of the TU2/TA2 welded joint.When the welding temperature is 860°C and the holding time is 75 min,the tensile strength of the TU2/Ni/Nb/TA2welded joint reaches the value of 93.5 MPa.The Ni/Nb intermediate layer improves the joint strength better than the TU2/TA2 joint when the Ni intermediate layer is added.However,the strength of the TU2/Ni/Nb/TA2 welded joint is significantly lower than that of the TU2/Nb/TA2 welded joint.The formation of diffusion layer at the interface of joints is determined by thermodynamic and dynamic conditions.The growth models of diffusion layer of various joints can be divided into three stages:physical contact stage,intermetallic compound or solid solution reaction layer formation stage and diffusion layer growth stage.The diffusion coefficients?D?and diffusion activation energies?Q?of Cu and Ti in the interfacial diffusion zone of Ti/Cu welded joints were calculated by Origin curve fitting and Boltzmann-Matano method.The order of formation of intermetallic compounds is Ti₂Cu,Cu₄Ti₃,CuTi and Cu₄Ti by the obtained diffusion coefficient?D?and diffusion activation energy?Q?in combination with kinetic driving conditions.The growth model of diffusion reaction layer in TU2/TA2 welded joint can be divided into three stages:physical contact,formation of Ti?ss.Cu?layer and formation of Ti₂Cu,Cu₄Ti₃,CuTi and Cu₄Ti intermetallic compound layer.The growth model of diffusion reaction layer in TU2/Ni/TA2 welded joint can be divided into five stages:physical contact,the formation of Ti?ss.Ni?solid solution,the formation of Ni₃Ti,NiTi and Ti₂Ni phases,growth of Ni₃Ti,NiTi and Ti₂Ni phases,and the formation of Widmanstatten structure??Ti and?+?Ti?on the side of partial titanium.The formation sequence of Ni₃Ti,NiTi and Ti₂Ni phases is Ni₃Ti,NiTi and Ti₂Ni.The growth model of diffusion reaction layer in TU2/Nb/TA2 welded joint can be divided into three stages:physical contact,the formation of beta-Ti,the formation of a+beta-Ti Widmanstatten structure and the formation of Cu-Nb diffusion layer.The growth model of diffusion reaction layer in TU2/Ni/Nb/TA2 welded joint can be divided into three stages:physical contact,formation of beta-Ti and Ni₃Nb?containing a small amount of Ni₆Nb₇?phase and formation of a+beta-Ti Widmanstatten structure.