Microstructure And Properties Of Ti₂AlNb/Ti60 Heterogenous Alloy Linear Friction Welded Joints

The temperature and stress of aero-engine components vary greatly during operation,so different mechanical properties need to be met at the same time.Linear friction welding is an advanced manufacturing technology that can not only achieve welding of heterogeneous materials,but also reduce or avoid welding defects caused by traditional welding methods.The present paper conduct LFW numerical simulation,LFW experiment and post-weld heat treatment research on Ti₂AlNb/Ti60,which are new engine materials.The main results are as follows:Based on the Ti₂AlNb/Ti60 two-dimensional model,the physical field and flash characteristics of the welding process under typical process parameters are simulated and studied.The results show that,the center temperature of the friction interface on the Ti60 side and Ti₂AlNb side rose rapidly to 1011°C and 1099°C,respectively,within 1s,and then the temperature became stable.The plastic metal material began to be extruded,and the axial shortening gradually increased.The stress value at the center point of the interface of the two alloys increases first and then decreases.The maximum equivalent stress on the Ti60 side and Ti₂AlNb side is mainly concentrated at the junction between the edge of the weldment and the fixture,and the maximum equivalent plastic strain is distributed at the friction interface.Ti₂AlNb and Ti60 alloys were welded by a linear friction welding machine under typical process parameters,and various test methods were used to analyze the structure and properties of the obtained heterogeneous joints.The results show that,the base metal zone on the Ti₂AlNb side is a typical B2+?₂+O three-phase forged structure.Compared with the base metal,the B2 phase is significantly increased in the thermomechanically affected zone,while the O phase and?₂phase are reduced.The structure of the weld zone is dominated by B2phase,and the number of?₂and O phases is small.The base metal zone on the Ti60 side is forged equiaxed structure.In the thermomechanically affected zone,part of the original?phase will be transformed into?phase,and needle-like?phase will be precipitated during the cooling process.The weld zone is mainly composed of fine?grains.The highest hardness value on the Ti₂AlNb side is appeared in the weld zone,and the lowest is appeared in the base metal zone.However,on the Ti60 side,the hardness of the weld zone is the highest,and the lowest is appeared in the thermomechanically affected zone.The heat treatment experiment was carried out on the Ti₂AlNb/Ti60 alloy linear friction welding joint under three heat treatment systems.The results show that,as the solid solution temperature increases,the base material zone and the thermomechanically affected zone on the Ti60 side will undergo the transition of???.The size of the primary?phase is reduced,and the growth of?grains is hindered.The primary?phase dissolves in the thermomechanically affected zone,and the secondary equiaxed?phase increases.As the solid solution temperature increases from 950°C to 980°C,the?₂phase in the base metal zone on the Ti₂AlNb side decomposes and the rim-O phase precipitates and gradually coarsens.After solution treatment at 1010°C,the size of the?₂phase becomes larger,and the number of coarsened O phases decreases.In the thermally affected zone,with the increase of the temperature,the?₂phase and the O phase gradually transform into the lath O phase,and the secondary needle-like O phase is coarsened.The?₂phase becomes larger in size after solution treatment at 1010?,and it is distributed in the B2 matrix in the form of slabs.With the increase of the solution temperature in the weld zone of Ti₂AlNb/Ti60 heterogeneous joint,the O??₂+B2 phase transition occurs on the Ti₂AlNb side,and the???phase transition occurs on the Ti60 side.The content of O/?phase in the weld zone structure gradually decreases,and the content of?₂phase and matrix phase increases.When the solution temperature is increased from 950°C to 1010°C,the overall microhardness of the joint decreases and the distribution changes similarly.