Study On The Characteristics Of Microstructure And Tensile Properties Of Titanium Alloy By Electron Beam Additive Manufacturing

Titanium alloy has been widely used in the field of aerospace due to its performance advantages.At the same time,the material manufacturing technology has obvious advantages in the formation of complex structural parts,reduce the processing procedures,shorten the processing cycle and so on.So it has a better application prospects in the domestic and foreign advanced manufacturing technology.Electron beam forming technology as a new technology remains to be further explored in the shape of the organization and mechanical properties.In this paper,TA3,TB5,TC4 titanium alloy was used as the substrate to fabricate the titanium alloy by electron beam welding.On this basis,the effect of the type of substrate on the microstructure,hardness and tensile strength of the molded article were focused on as well as the variation of tensile strength at the Forming Layer-Substrate interface.Wire feeding speed,depositing way and beam intensity are the main parameters affecting Single-channel multi-layer forming.When the wire feeding speed is Vs=20mm/s,the single wall specimen of 60 layers can be obtained by properly reducing the beam current and combining single and bidirectional depositing way.The characteristics of fused lines and layers morphology are observed on the cross section of the specimen.And there are stripe ? phase and residual ? composition of the basketwave structure on the forming-layer which microhardness value fluctuates between 260HV³00HV,all of that are changed periodically in the height of 5mm forming.There is a thick ? columnar crystal grown along the epitaxial growth on the forming layer,which is made of ?-phase and the residual ? phase composition of basketwave structure.When the number of layers is less than 5,the length and width of the columnar crystals increase with the increase of the number of layers.The primary ?phase and the acicular martensite ? are gradually reduced to secondary slender acicular? composition basketwave structure,the average size of which are reduced form2.24?m when forming 1-layer to 1.27?m when forming 5-layer.Crystal orientation of which is mainly changed from <0001> and <12-30> between the crystal direction between the <0001> and <01-11> crystal direction and the maximum density of whichis increased from 30.14 to 46.8,and the texture has been strengthened after 5 times the thermal cycle.When the number of layers is less than 10 layers,the type of substrate has a great influence on the microstructure and hardness of the forming layer.Forming Layer on the TC4 substrate(Referred to FL_TC4)has the largest columnar size,followed by FL_TA3,and FL_TB5is the smallest.FL_TA3and FL_TC4are mainly composed of Lamellar? transition structure consisting of strip ?-phase and elongated acicular ?-phase,while a large number of short acicular martensite ? has existed on the FL_TB5.The change trend of microhardness is that FL_TB5is greater than the FL_TC4,while FL_TA3is the smallest.when the number of layers is less than 5 layers the difference of microhardness on the forming layer is the biggest: The hardness of FL?TA5?is about 370 HV,while the hardness of FL_TA3and FL_TC4is about 300 HV,when the number of layers is higher than 5-layer,the difference in microhardness between the forming layers of different substrates is reduced and the difference of microhardness value is about 20 HV.All of that is mainly resulted from the diffusion of elements between the substrate and the forming layer.The tensile strength of the forming layer of different substrates is about the same that the value is about 800 Mpa,and the elongation is more than 20%,which is slightly lower than the annealed TC4 substrate,but still has good strength and plasticity as a whole.The fracture morphology of the formed layer is dimple,and the fracture mode is ductile fracture,which is the same as that of the TC4 substrate.The strength of the interface between the substrate and the molding layer is higher than that of the substrate or the Forming layer as well as has good strength and plasticity.Forming layer-TA3 substrate interface fracture on the TA3 substrate transition zone and the fracture mode is quasi-cleavage fracture.Forming layer-TB5 substrate interface fracture in the TB5 substrate transition zone and the fracture mode is cleavage fracture.However,the fracture of the interface layer of the molding layer-TC4 is on the side of the molding layer and the fracture is ductile fracture.