Research On Interfacial Effect Induced By Phase Transformation During Superplastic Diffusion Bonding Between Ti₂AlNb And Ti Alloys

In view of microstructure and properties deterioration during conventional diffusion bonding with high temperature and long time,the project proposes toincrease the diffusion bonding rate using phase transformation superplasticdiffusion bonding technology.For this technology,it is the key that clarifying the interfacial effect induced by phase transformation during the superplastic diffusion bonding,which is investigated deficiently by now.In view of this,this project is to study the interfacial effect induced by phase transformation during superplastic diffusion bonding between Ti2AlNb and Ti Alloys.The enhancement of superplastic diffusion bonding by phase transformation is to be revealed.This can help increase the diffusion bonding rate at lower temperatures.The project researched the isothermal and phase transformation superplastic diffusion bonding of TC4 and TC4,Ti2AlNb and TC4 under non vacuum condition.And the isothermal diffusion bonding joints of Ti2AlNb and TC4 carried out post-weld heat treatment.The interface structure,fracture morphology and mechanical properties of the joints were studied by lekal metallurgical microscope,scanning electron microscopy(SEM)and electronic universal testing machine.The formation of diffusion bonding TC4 alloy weld zone at the interface of Ti and O films can be damaged under high temperature and high pressure,therefore,in the non vacuum oxide has little effect on the strength of TC4/TC4 joints.Within a certain time and temperature,with the increase of holding time and temperature of the connection,TC4/TC4 isothermal superplastic diffusion bonding joint microstructure more uniform duplex microstructure,properties of joints increases,the shear strength can reach 573 MPa under the condition of t=2 h,p=10 MPa,T=950 ℃,and the tensile strengtht is 832 MPa.The phase transformation superplastic diffusion bonding of TC4 alloy in the temperature range of 850 ℃～950 ℃ was better,the joint shear strength can reach 612 MPa under the condition of Tmax=950 ℃,Tmin=850 ℃,N=3,t=20 min,p=10 MPa,the ensile strengtht is 893 MPa.Ti2AlNb and TC4 conducted isothermal and phase transformation superplastic diffusion bonding and its post-weld heat treatment.The results show that the performance of Ti2AlNb/TC4 isothermal diffusion bonding joint is poor,and its tensile strength is only 492 MPa in the holding time 1～2 h.While the Ti2AlNb/TC4 phase transformation superplastic diffusion bonding joints have better performance;The optimum process parameter of Ti2AlN/TC4 phase transformation superplastic diffusion bonding joint is Tmax=950 ℃,Tmin=850 ℃,N=3,t=20 min,its tensile strength can reach 789 MPa.Therefore,the phase change can improve the performance of the joints,to achieve low temperature fast connection.Post-weld heat treatment can further improve the joint property under the condition of T= 950 ℃,t=2.5 h,its tensile strength is up to 897 MPa.