Study On The Relationship Between Mechanical Properties And The Microstructures Of The Electron Beam Welding Of The Dissimilar Titanium Alloys

Titanium alloy were widely used in the manufacture of engine rotor and compressor disc because of its high specific strength,low density and good corrosion resistance.Compared with traditional welding methods,such as argon tungsten-arc welding and submerged arc welding,the electron beam welding has unique advantages in connection of titanium alloy sheet due to its unique advantages such as high depth-to-width ratio,high welding efficiency,small heat affected zone and vacuum.Dissimilar titanium alloys has attract much attention because of the fact that the similar titanium alloy joints obtained by electron beam welding can't meet the requirements.Moreover,there are very few reports about the dissimilar titanium joints welded by electron beam at home and abroad.Therefore,electron beam welding of TC4 and TC11 sheets with 10 mm thickness have been carried out to analyze the microstructure and properties of the jointsOptical microscope,scanning electron microscope and microhardness tester are used to analyze the microstructure and texture,tensile properties,fatigue behavior and the effect of pre strain on the texture distribution in different regions and the fracture surface of joints.After electron beam welding,the microstructure of the weld was a lath martensite ?? phase.The microstructure of TC11 side at the heat affected zone was residual ? phase and lath martensite,while the microstructure of the TC4 side at heat affected zone showed basically a lath martensite.Texture existed in weld and heat affected zone.The microhardness of weld seam was the highest,while the microhardness at both heat affected zone decreased with the increase of the weld distance.The tensile stress-strain curves of TC4 base metal,TC11 base metal and TC4/TC11 joints were smooth and continuous at room temperature.The yield strength and tensile strength of TC11 base metal were the highest,followed by the joints,while the TC4 base metal was the lowest.Prestrain showed a certain effect on the cyclic hysteresis loop of joint and base metal.Without prestrain,the cyclic hysteresis loop of the joint and the base metal was basically symmetrical.With the increase of the prestrain,the maximum stress values of the base metal and the joint did not change obviously in the tensile stage,while they decreased at the compression stage,and the differences between them also decrease.The cyclic stress amplitudes of the base metal and the joint decreased with the increase of prestrain.The larger the prestrain,the lower the fatigue life of the joint.But the fatigue life of TC4 and TC11 base metal did not change significantly.Compared with the base metal,the fatigue life of the joint was more dispersive.When the number of cycles increased gradually,both the joint and the base metal occurred cyclic softening.The fracture surface of the joint was characterized by fatigue striation and ductile fracture.The c-axis of ?-phase textures including pre-fatigue deformation zone and post-fatigue fracture zone were deflected into Z0 direction after the pre-deformation treatment,with the phase of ? unchanging generally,and the textures within the fusion zone remained unchanged between the post-fatigue and pre-fatigue.