Research On TC4 Titanium Alloy Wire For Arc Additive Manufacturing

TC4 titanium alloy is the most widely used titanium alloy with excellent mechanical properties and high corrosion resistance.As the additive manufacturing technology can be formed at one time,for the more expensive titanium alloys,additive manufacturing can reduce material loss in the forming process of parts,thus reducing the costs.In this paper,the titanium alloy samples with various composition were prepared by the rapid solidification method.Three components were selected to prepare the wire according to the microstructure and properties of the rapid solidification molding conditions.The study on the microstructure and mechanical properties of its TIG(Argon tungsten arc welding)additive bodies was carried out.Subsequently,the microstructure and properties of the additive bodies after heat treatment were studied by annealing and solid solution + aging treatment.The main research results are as follows:(1)The additional addition of vanadium,silicon,and iron will refine the original β grains in the TC4 titanium alloy under rapid solidification conditions,and the β crystals are mainly composed of metastable phases such as α’.TC4 titanium alloy has a strength of 908 MPa and a plasticity of 4%.Furthermore,the TC4 titanium strength with the addition of vanadium and silicon increased by 16% and 33%,respectively.And the TC4 titanium alloy with the addition of iron has the slightly-increased strength and improved plasticity of 20%.Combining the growth inhibitory factor(Q)of each element in titanium and the mechanical properties under rapid solidification conditions,three different wires were prepared by selecting the median TC4 component and adding 0.4 wt.% vanadium and 0.2 wt.% iron and have been verified that all three kinds of wires meet the GB/T 30562-2014 standard.(2)The microstructure in the steady-state region was analyzed and exhibits a heat-treated state due to the "intrinsic heat treatment" feature in the arc additive manufacturing titanium alloy.The macrostructure retains columnar β grain and the inside of the β crystal grains is dominated by the mesh basket structure,which contains a small amount of clustered structure with a characteristic of rapid solidification.A large number of dot-like β phases(tens of nanometers to hundreds of nanometers)are precipitated inside the α phase in the mesh basket structure.After the addition of iron,the size of the α phase particles has been reduced by 42%;compared with the rapid solidification of the solid state,the strength and plasticity has been greatly improved(944 MPa,9%);the strength and plasticity of the vanadium-added and the TC4 additive are almost the same,The strength of the iron-added additive body has been reduced to a certain extent,but the plasticity has increased to 27%.(3)After annealing of the three-component additive body,the α’ phase is basically eliminated and the proportion of the cluster structure is reduced.The α phase is gradually coarsened and the spot β phase is reduced.The block β phase is produced under the annealing process at 920 ℃×2 h.After the optimal process parameters for 850 ℃×2 h furnace cooling,the microhardness of all the additive bodies is reduced,the strength of the TC4 additive specimens in the horizontal direction is reduced and the plasticity in the vertical direction is slightly increased.The plasticity of the vanadium additive body is increased to 13% and the strength is basically unchanged.The strength of the additive body with an addition of Fe is increased by nearly 100 MPa after annealing.(4)After solid solution + aging treatment of the three additive bodies,the solid solution state mainly contains α/α’ clustered structure and the block β phase generated at high temperature is retained.After aging,the clustered structure disappears and dots β phase is produced.α phase coarsens with the increase of solid solution temperature and interlaced αphase is precipitated inside the bulk β phase,forming the double interlaced structure of the micron-level interlaced α phase in the initial β crystal grain and the micro-nano-level interlacedα phase in the bulk β phase.After selecting the best process parameters(920 ℃×1 h+water cooling+530 ℃×4 h+air cooling),the horizontal strength of the TC4 additive sample increases by 50 MPa.The tensile strength of the TC4 additive sample with the addition of vanadium increased by 60 MPa,and the plasticity was also greatly increase to 11%.The strength of the iron-added additive body was increased by 60 MPa,but the plasticity was greatly reduced.