Microstructure And Mechanical Properties Of Linear Friction Welding Joint Of TC17 Titanium Alloy

As a new type of aero-engine structure,blisk plays an important role in improving engine safety,reliability and working life,as well as improving the thrust weight ratio of aero-engine.It has been widely used in military and civil aeroengines produced by advanced aero-engine manufacturers such as GE,Pratt Whitney and Rollo.As a high-quality welding method,linear friction welding has unique technical advantages in manufacturing blisk and repairing damaged blades,which has become a main manufacturing method for blisk.In this paper,based on the manufacturing requirements of aero-engine blisk,the linear friction welding of TC17 titanium alloy was carried out.The effects of welding process on joint forming,microstructure characteristics of micro zone and post weld heat treatment on Microstructure and properties of joint were studied.High strength linear friction welded joint was obtained,which provided technical support for the design and manufacture of aero-engine in China.The changing trend of parameters in linear friction welding process and the influence of working speed on the macro forming of specimen are studied.It is found that only by reasonably matching the relationship between welding heat input and welding speed,can the welding defects such as cracks,non-welded,holes and nodular oxides be avoided,so as to ensure the welding quality of the joint.The microstructure characteristics of TC17 titanium alloy linear friction welded joint were studied by electron probe microanalysis(EPMA)and electron backscatter diffraction(EBSD).It was found that the weld zone was composed of equiaxed microstructure f'ormed by incomplete dynamic recrystallization and residual deformed?-grains after severe deformation.The grain orientation distribution was disordered,and the dynamic recrystallization process did not occur in the thermo mechanical affected zone In addition to the original deformed P grain boundary,there are all small angle grain boundaries in the ? grain.The large and small angle grain boundaries are interphase in the weld area,and there are a lot of small angle grain boundaries in the residual deformed ? grains.Through the control of microstructure and mechanical properties,it is found that the tensile fracture position of welded joint at room temperature is in the welding zone,the tensile strength is obviously lower than the base metal,the plasticity is very low,the fracture is brittle fracture mode,the fracture mechanism is quasi cleavage;after post weld heat treatment,due to the decomposition of metastable ? phase and metastable a phase,the joint is strengthened to a certain extent,The results show that the tensile strength and plasticity of the joint are significantly improved,reaching the same level as the base metal,and the fracture surface is in the form of ductile fracture;the microstructure distribution of ?+? basket after heat treatment is closely related to the heat treatment temperature and time,and determines the comprehensive properties of the joint.